We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd rather
not try it.

Would appreciate any help.

"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from ebay.
It didn't have a power cord. It says it's a 12v dc 2.5a but it doesn't
give the polarity. A person from gateway said he thought it wouldn't hurt
the monitor if it got plugged in backwards but I'd rather not try it.

Would appreciate any help.

If it has got any external metal parts such as RCA (phono) connector outers,
BNC connector outers, 'D' connector surround etc, or possibly screws for a
stand, as these often go right through the plastic case, and into the
internal chassis, then try measuring from any such metal to each of the DC
power input connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground ( "-" )
connection. The other will then be the "+". Assuming that it's a 'standard'
co-axial DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you are
obtaining a replacement PSU, that the plug is often a slightly abnormal
size, being a little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the job, as these
monitors do draw quite a lot of current, and may well surge up close to the
quoted 2.5 amps at startup, as the LCD backlights first fire up before
settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like to
say. Some equipment is perfectly well protected against such 'consumer
antics', but it is by no means guaranteed, and if it is not adequately
protected, the result is often an item that's fried beyond repair, for no
other reason than unobtainable power supply devices, as many previous posts
on this subject over the years, will attest ...

Arfa

"Arfa Daily" wrote in message
...

If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or possibly
screws for a stand, as these often go right through the plastic case,
and into the internal chassis, then try measuring from any such metal to
each of the DC power input connector's terminals in turn, using an ohm
meter. Chances are you'll find a direct connection, and that will be your
DC ground ( "-" ) connection. The other will then be the "+".

Arfa, you're usually dead-on, but this is quite incorrect. The side of the
connector that's "grounded" is not necessarily negative! A transistor radio
using PNP transistors would (presumably) have a positive ground, not
negative.


Assuming that it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's not cast
in
stone.

No, it's not. I have Sony equipment where the pin is negative, not positive.


Rather than seeing which side of the power connector is grounded, I would
look to see which side of the electrolytic capacitors is grounded.

"William Sommerwerck" wrote in message
. ..
"Arfa Daily" wrote in message
...

If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or possibly
screws for a stand, as these often go right through the plastic case,
and into the internal chassis, then try measuring from any such metal to
each of the DC power input connector's terminals in turn, using an ohm
meter. Chances are you'll find a direct connection, and that will be your
DC ground ( "-" ) connection. The other will then be the "+".

Arfa, you're usually dead-on, but this is quite incorrect. The side of the
connector that's "grounded" is not necessarily negative! A transistor
radio
using PNP transistors would (presumably) have a positive ground, not
negative.


I think you'll find that on 'most' modern - and I did say "modern" in my
original reply - equipment, this has been pretty much standardised such that
DC "-" *is* common ground. Sony kit that I have seen in recent years has all
obeyed this 'convention', so I'm willing to bet that any Sony items that
follow the opposite 'convention', are not "modern". Pin = "-" used to be the
'convention', but for all mainstream manufacturers whose equipment I work
on, this has not been the case for many years. It was only usually the
Japanese manufacturers that followed this anyway, as I recall.

As for a transistor radio that uses PNP transistors, I haven't seen one that
uses transistors at all for many years, let alone PNP ones, so I think you
might be struggling to fit that into my "modern" category, also.




Assuming that it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's not cast
in
stone.

No, it's not. I have Sony equipment where the pin is negative, not
positive.


Rather than seeing which side of the power connector is grounded, I would
look to see which side of the electrolytic capacitors is grounded.


This is, of course, the very best way, if the owner wants the trouble of
taking it all to bits, and identifying a suitable electrolytic to use as his
reference. However, I would put my name on the line that the method I quoted
before, would 99.5% yield the same result, with any 'modern' item using a
coaxial DC socket. Perhaps someone out there with a Gateway monitor could
confirm which way round it is, then neither of us will be applying guesswork
to experience and coming up with sage advice ... d;~}

Arfa

In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't seen
one that uses transistors at all for many years, let alone PNP ones,
so I think you might be struggling to fit that into my "modern"
category, also.

Well Arfa... they still use transistors (both NPN and PNP types) in
modern equipment. The reason you don't see them anymore is do to the
magic of minturization. But they are still there, just neatly packaged
into what is known today as the intergrated circuit (IC chip).

--
Bill

"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't seen
one that uses transistors at all for many years, let alone PNP ones,
so I think you might be struggling to fit that into my "modern"
category, also.

Well Arfa... they still use transistors (both NPN and PNP types) in modern
equipment. The reason you don't see them anymore is do to the magic of
minturization. But they are still there, just neatly packaged into what is
known today as the intergrated circuit (IC chip).

--
Bill
And I though I was pedantic !! Yes, of course ICs contain transistors, and
yes, I would accept that some of them may be PNP types, depending on block
function within the IC, but I don't think, with the best will in the world,
that this is the level of transistor existence that William was referring to
with his "transistor radio using PNP transistors" scenario. In any event, in
the case of an IC taking a single polarity rail, it is irrelevant whether
the transistors inside are NPN or PNP or FETs or whatever. PNP transistors
are just used 'upside down', as are discrete PNP transistors when used in
any piece of single polarity rail equipment. The ground is still (typically
for //modern// equipment) the "-" side of the power supply / battery.

Anyway, this is getting out of hand. The OP aked a simple question, and I
gave a simple answer. This afternoon, I was in a friend's computer repair
shop. Bear in mind that he deals with monitors of all types and makes on a
daily basis. I asked him how he would go about determining the polarity of
such a monitor, and he said that he would stick one side of his ohm meter on
one of the D connector locking screws, and the other on each pin of the DC
connector. When he found the pin that read short to the connector locking
screw, it was his contention that he would have identified the "-" side of
the power supply. So that's pretty much exactly what I said. He also frowned
and shook his head, and said that he couldn't remember how many years it had
been since he had seen a DC connector that had the pin as the "-".

Which is also pretty much what I said ...

Arfa

zirath wrote:

We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd rather
not try it.

Would appreciate any help.


http://www.lcdpayless.com/productpage.php?productId=237 shows it as
12 VDC 3.5 A center positive.


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On 3ÔÂ28ÈÕ, ÏÂÎç4ʱ45·Ö, zirath wrote:
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd rather
not try it.

Would appreciate any help.



Do you want access to China's massive pool of electronic
manufacturers... but lack the time to contact suppliers, negotiate
contracts, arrange shipping or monitor product quality? Don't worry -
Let seriouswholesale deal with all that for you.

*Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD /
Audio, and Computer Accessories now by visiting the online wholesale
catalog at seriouswholesale. com You'll have peace of mind thanks to
the seriouswholesale Quality Control, 12-month Warranty on all
products, and easy secure payment by credit card through Paypal.

Selling on eBay or your own online store? Send products direct from
our warehouse to your customers using our unique drop-shipping
service. You can profit by selling hundreds of different products,
without holding any of your own inventory! Any questions you have will
be answered by the seriouswholesale English-speaking customer support
team... Their aim is to make your China electronics importing business
easier to run than ever before.

Welcome to http://www.seriouswholesale.com.

seriouswholesale - Buy from the source, profit without the hassle.

- 12 Months Warranty - No minimum order restrictions - Drop-shipping
with no additional fee - Pay by safely by PayPal seriouswholesale
Wholesale Co., Ltd.: Chinas original and best online electronics
wholesaler & drop-shipper: seriouswholesale. com

On the monitor it should be marked or say something
in the manual.

"The Lady from Philadelphia" forgot the obvious. Power sockets almost always
have their polarity marked.

"James Sweet" wrote in message
news:kjhHj.461$oE1.370@trndny09...


"William Sommerwerck" wrote in message
. ..
On the monitor it should be marked or say something
in the manual.

"The Lady from Philadelphia" forgot the obvious. Power sockets almost
always
have their polarity marked.



I've certainly seen plenty of them that didn't though.

Likewise

Arfa

"William Sommerwerck" wrote in message
. ..
On the monitor it should be marked or say something
in the manual.

"The Lady from Philadelphia" forgot the obvious. Power sockets almost
always
have their polarity marked.



I've certainly seen plenty of them that didn't though.

On 3ÔÂ28ÈÕ, ÏÂÎç4ʱ45·Ö, zirath wrote:
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd rather
not try it.

Would appreciate any help.



Do you want access to China's massive pool of electronic
manufacturers... but lack the time to contact suppliers, negotiate
contracts, arrange shipping or monitor product quality? Don't worry -
Let seriouswholesale deal with all that for you.

*Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD /
Audio, and Computer Accessories now by visiting the online wholesale
catalog at seriouswholesale. com You'll have peace of mind thanks to
the seriouswholesale Quality Control, 12-month Warranty on all
products, and easy secure payment by credit card through Paypal.

Selling on eBay or your own online store? Send products direct from
our warehouse to your customers using our unique drop-shipping
service. You can profit by selling hundreds of different products,
without holding any of your own inventory! Any questions you have will
be answered by the seriouswholesale English-speaking customer support
team... Their aim is to make your China electronics importing business
easier to run than ever before.

Welcome to http://www.seriouswholesale.com.

seriouswholesale - Buy from the source, profit without the hassle.

- 12 Months Warranty - No minimum order restrictions - Drop-shipping
with no additional fee - Pay by safely by PayPal seriouswholesale
Wholesale Co., Ltd.: Chinas original and best online electronics
wholesaler & drop-shipper: seriouswholesale. com

zirath wrote:
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd rather
not try it.

Would appreciate any help.

Thanks to everyone for your help.

In ,
Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't seen
one that uses transistors at all for many years, let alone PNP ones,
so I think you might be struggling to fit that into my "modern"
category, also.

Well Arfa... they still use transistors (both NPN and PNP types) in
modern equipment. The reason you don't see them anymore is do to the
magic of minturization. But they are still there, just neatly
packaged into what is known today as the intergrated circuit (IC
chip).

And I though I was pedantic !! Yes, of course ICs contain
transistors, and yes, I would accept that some of them may be PNP
types, depending on block function within the IC, but I don't think,
with the best will in the world, that this is the level of transistor
existence that William was referring to with his "transistor radio
using PNP transistors" scenario. In any event, in the case of an IC
taking a single polarity rail, it is irrelevant whether the
transistors inside are NPN or PNP or FETs or whatever. PNP
transistors are just used 'upside down', as are discrete PNP
transistors when used in any piece of single polarity rail equipment.
The ground is still (typically for //modern// equipment) the "-" side
of the power supply / battery.
Anyway, this is getting out of hand. The OP aked a simple question,
and I gave a simple answer. This afternoon, I was in a friend's
computer repair shop. Bear in mind that he deals with monitors of all
types and makes on a daily basis. I asked him how he would go about
determining the polarity of such a monitor, and he said that he would
stick one side of his ohm meter on one of the D connector locking
screws, and the other on each pin of the DC connector. When he found
the pin that read short to the connector locking screw, it was his
contention that he would have identified the "-" side of the power
supply. So that's pretty much exactly what I said. He also frowned
and shook his head, and said that he couldn't remember how many years
it had been since he had seen a DC connector that had the pin as the
"-".
Which is also pretty much what I said ...

Arfa

That would be okay if it were a negative ground system. But like what
William Sommerwerck mentioned, we don't know that. The way I would do it
is to ohm the the power in. And the lower resistance would be the
correct polarity. Although you would need another meter to read the
polarity of the ohm meter. As they are not standardized on multimeters.
You could also use a diode (or LED) to learn of the polarity of the
meter as well.

--
Bill

"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't seen
one that uses transistors at all for many years, let alone PNP ones,
so I think you might be struggling to fit that into my "modern"
category, also.

Well Arfa... they still use transistors (both NPN and PNP types) in
modern equipment. The reason you don't see them anymore is do to the
magic of minturization. But they are still there, just neatly
packaged into what is known today as the intergrated circuit (IC
chip).

And I though I was pedantic !! Yes, of course ICs contain
transistors, and yes, I would accept that some of them may be PNP
types, depending on block function within the IC, but I don't think,
with the best will in the world, that this is the level of transistor
existence that William was referring to with his "transistor radio
using PNP transistors" scenario. In any event, in the case of an IC
taking a single polarity rail, it is irrelevant whether the
transistors inside are NPN or PNP or FETs or whatever. PNP
transistors are just used 'upside down', as are discrete PNP
transistors when used in any piece of single polarity rail equipment.
The ground is still (typically for //modern// equipment) the "-" side
of the power supply / battery.
Anyway, this is getting out of hand. The OP aked a simple question,
and I gave a simple answer. This afternoon, I was in a friend's
computer repair shop. Bear in mind that he deals with monitors of all
types and makes on a daily basis. I asked him how he would go about
determining the polarity of such a monitor, and he said that he would
stick one side of his ohm meter on one of the D connector locking
screws, and the other on each pin of the DC connector. When he found
the pin that read short to the connector locking screw, it was his
contention that he would have identified the "-" side of the power
supply. So that's pretty much exactly what I said. He also frowned
and shook his head, and said that he couldn't remember how many years
it had been since he had seen a DC connector that had the pin as the
"-".
Which is also pretty much what I said ...

Arfa

That would be okay if it were a negative ground system. But like what
William Sommerwerck mentioned, we don't know that. The way I would do it
is to ohm the the power in. And the lower resistance would be the correct
polarity. Although you would need another meter to read the polarity of
the ohm meter. As they are not standardized on multimeters. You could also
use a diode (or LED) to learn of the polarity of the meter as well.

--
Bill

JHC !!! Do you not understand the word "modern" ? Do you not understand the
phrase "... deals with monitors of all types on a daily basis" ? I repair
this stuff all day every day for a living. I have done for over 35 years. I
cannot remember the last time I saw a piece of kit of any description, which
employed a positive ground. My friend, who owns a computer repair shop, and
has done for many years, cannot remember the last time - if ever - that he
saw a monitor with an external power supply, that was not negative ground
with the connector sleeve as the negative connection.

With so much interconnectivity between household items now, there has had to
be a degree of standardisation on this issue, and it has evolved through a
general concensus amongst manufacturers, that negative ground will be the
convention.

As for your method of determining polarity, it makes no sense at all, unless
you are assuming a series diode, which is quite unlikely in most modern kit,
as it represents a waste of power due to its forward voltage drop. It may
even have a shunt protection diode, in which case, your 'test' will ensure
that the polarity is determined INcorrectly. Even if the device did have a
series diode, depending on where the supply first goes, there is still no
guarantee that there will be any reading at all on a standard multimeter on
ohms. If there is not any diode - series or shunt - any reading of ohms
obtained across the input socket, is unlikely to reveal anything meaningful.
What is your experience in fault-finding, I wonder, to have caused you to
have formulated such a bizarre method, and believe that it would
uncategorically give you a correct result ?

Arfa

Arfa Daily wrote:

JHC !!! Do you not understand the word "modern" ? Do you not understand the
phrase "... deals with monitors of all types on a daily basis" ? I repair
this stuff all day every day for a living. I have done for over 35 years. I
cannot remember the last time I saw a piece of kit of any description, which
employed a positive ground. My friend, who owns a computer repair shop, and
has done for many years, cannot remember the last time - if ever - that he
saw a monitor with an external power supply, that was not negative ground
with the connector sleeve as the negative connection.

With so much interconnectivity between household items now, there has had to
be a degree of standardisation on this issue, and it has evolved through a
general concensus amongst manufacturers, that negative ground will be the
convention.

As for your method of determining polarity, it makes no sense at all, unless
you are assuming a series diode, which is quite unlikely in most modern kit,
as it represents a waste of power due to its forward voltage drop. It may
even have a shunt protection diode, in which case, your 'test' will ensure
that the polarity is determined INcorrectly. Even if the device did have a
series diode, depending on where the supply first goes, there is still no
guarantee that there will be any reading at all on a standard multimeter on
ohms. If there is not any diode - series or shunt - any reading of ohms
obtained across the input socket, is unlikely to reveal anything meaningful.
What is your experience in fault-finding, I wonder, to have caused you to
have formulated such a bizarre method, and believe that it would
uncategorically give you a correct result ?


I guess that no one bothered to check out the link I posted to a
replacement supply that not only shows it to be center positive, but it
tells you which coaxial power plug you need.


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In ,
Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't
seen one that uses transistors at all for many years, let alone
PNP ones, so I think you might be struggling to fit that into my
"modern" category, also.

Well Arfa... they still use transistors (both NPN and PNP types) in
modern equipment. The reason you don't see them anymore is do to
the magic of minturization. But they are still there, just neatly
packaged into what is known today as the intergrated circuit (IC
chip).

And I though I was pedantic !! Yes, of course ICs contain
transistors, and yes, I would accept that some of them may be PNP
types, depending on block function within the IC, but I don't think,
with the best will in the world, that this is the level of
transistor existence that William was referring to with his
"transistor radio using PNP transistors" scenario. In any event, in
the case of an IC taking a single polarity rail, it is irrelevant
whether the transistors inside are NPN or PNP or FETs or whatever.
PNP transistors are just used 'upside down', as are discrete PNP
transistors when used in any piece of single polarity rail
equipment. The ground is still (typically for //modern// equipment)
the "-" side of the power supply / battery.
Anyway, this is getting out of hand. The OP aked a simple question,
and I gave a simple answer. This afternoon, I was in a friend's
computer repair shop. Bear in mind that he deals with monitors of
all types and makes on a daily basis. I asked him how he would go
about determining the polarity of such a monitor, and he said that
he would stick one side of his ohm meter on one of the D connector
locking screws, and the other on each pin of the DC connector. When
he found the pin that read short to the connector locking screw, it
was his contention that he would have identified the "-" side of
the power supply. So that's pretty much exactly what I said. He
also frowned and shook his head, and said that he couldn't remember
how many years it had been since he had seen a DC connector that
had the pin as the "-".
Which is also pretty much what I said ...

Arfa

That would be okay if it were a negative ground system. But like what
William Sommerwerck mentioned, we don't know that. The way I would
do it is to ohm the the power in. And the lower resistance would be
the correct polarity. Although you would need another meter to read
the polarity of the ohm meter. As they are not standardized on
multimeters. You could also use a diode (or LED) to learn of the
polarity of the meter as well. --
Bill

JHC !!! Do you not understand the word "modern" ? Do you not
understand the phrase "... deals with monitors of all types on a
daily basis" ? I repair this stuff all day every day for a living. I
have done for over 35 years. I cannot remember the last time I saw a
piece of kit of any description, which employed a positive ground. My
friend, who owns a computer repair shop, and has done for many years,
cannot remember the last time - if ever - that he saw a monitor with
an external power supply, that was not negative ground with the
connector sleeve as the negative connection.
With so much interconnectivity between household items now, there has
had to be a degree of standardisation on this issue, and it has
evolved through a general concensus amongst manufacturers, that
negative ground will be the convention.

As for your method of determining polarity, it makes no sense at all,
unless you are assuming a series diode, which is quite unlikely in
most modern kit, as it represents a waste of power due to its forward
voltage drop. It may even have a shunt protection diode, in which
case, your 'test' will ensure that the polarity is determined
INcorrectly. Even if the device did have a series diode, depending on
where the supply first goes, there is still no guarantee that there
will be any reading at all on a standard multimeter on ohms. If there
is not any diode - series or shunt - any reading of ohms obtained
across the input socket, is unlikely to reveal anything meaningful.
What is your experience in fault-finding, I wonder, to have caused
you to have formulated such a bizarre method, and believe that it
would uncategorically give you a correct result ?
Arfa

Actually being an electrical engineer for 35 years, I could careless how
long your friend has been repairing computers. And the reason why the
ohm meter works is because all of the curcuits are in parallel with the
supply. Thus you will get a lower reading when the polarity is correct.
And you will get a higher reading when it is not correct. Thus as all of
the circuits are reversed biased.

Whether or not all manufactures use negative ground or not, I have no
idea. Although in all of my experience, I have learned to never assume
anything. And I have seen many strange designs. One of them had an OP
amp's output connected directly to ground. I was confused about that one
until I chatted with the designer. Then it all made sense.

--
Bill

JHC !!! Do you not understand the word "modern" ? Do you not understand
the phrase "... deals with monitors of all types on a daily basis" ? I
repair this stuff all day every day for a living. I have done for over 35
years. I cannot remember the last time I saw a piece of kit of any
description, which employed a positive ground. My friend, who owns a
computer repair shop, and has done for many years, cannot remember the
last time - if ever - that he saw a monitor with an external power supply,
that was not negative ground with the connector sleeve as the negative
connection.

With so much interconnectivity between household items now, there has had
to be a degree of standardisation on this issue, and it has evolved
through a general concensus amongst manufacturers, that negative ground
will be the convention.

As for your method of determining polarity, it makes no sense at all,
unless you are assuming a series diode, which is quite unlikely in most
modern kit, as it represents a waste of power due to its forward voltage
drop. It may even have a shunt protection diode, in which case, your
'test' will ensure that the polarity is determined INcorrectly. Even if
the device did have a series diode, depending on where the supply first
goes, there is still no guarantee that there will be any reading at all on
a standard multimeter on ohms. If there is not any diode - series or
shunt - any reading of ohms obtained across the input socket, is unlikely
to reveal anything meaningful. What is your experience in fault-finding, I
wonder, to have caused you to have formulated such a bizarre method, and
believe that it would uncategorically give you a correct result ?

Arfa


I've been working on this stuff for years as well, not as long as you, but I
haven't been alive as long as you've been at it either. I've never seen a
positive ground either, it would make no sense to do it that way. It's just
standard that this stuff is negative ground, and that metal parts of the
chassis are grounded for shielding, I've never once seen a case where this
wasn't true so it's good enough for me. If one is still in doubt, pop the
cover off and check the polarity of the filter lytics.

"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't
seen one that uses transistors at all for many years, let alone
PNP ones, so I think you might be struggling to fit that into my
"modern" category, also.

Well Arfa... they still use transistors (both NPN and PNP types) in
modern equipment. The reason you don't see them anymore is do to
the magic of minturization. But they are still there, just neatly
packaged into what is known today as the intergrated circuit (IC
chip).

And I though I was pedantic !! Yes, of course ICs contain
transistors, and yes, I would accept that some of them may be PNP
types, depending on block function within the IC, but I don't think,
with the best will in the world, that this is the level of
transistor existence that William was referring to with his
"transistor radio using PNP transistors" scenario. In any event, in
the case of an IC taking a single polarity rail, it is irrelevant
whether the transistors inside are NPN or PNP or FETs or whatever.
PNP transistors are just used 'upside down', as are discrete PNP
transistors when used in any piece of single polarity rail
equipment. The ground is still (typically for //modern// equipment)
the "-" side of the power supply / battery.
Anyway, this is getting out of hand. The OP aked a simple question,
and I gave a simple answer. This afternoon, I was in a friend's
computer repair shop. Bear in mind that he deals with monitors of
all types and makes on a daily basis. I asked him how he would go
about determining the polarity of such a monitor, and he said that
he would stick one side of his ohm meter on one of the D connector
locking screws, and the other on each pin of the DC connector. When
he found the pin that read short to the connector locking screw, it
was his contention that he would have identified the "-" side of
the power supply. So that's pretty much exactly what I said. He
also frowned and shook his head, and said that he couldn't remember
how many years it had been since he had seen a DC connector that
had the pin as the "-".
Which is also pretty much what I said ...

Arfa

That would be okay if it were a negative ground system. But like what
William Sommerwerck mentioned, we don't know that. The way I would
do it is to ohm the the power in. And the lower resistance would be
the correct polarity. Although you would need another meter to read
the polarity of the ohm meter. As they are not standardized on
multimeters. You could also use a diode (or LED) to learn of the
polarity of the meter as well. --
Bill

JHC !!! Do you not understand the word "modern" ? Do you not
understand the phrase "... deals with monitors of all types on a
daily basis" ? I repair this stuff all day every day for a living. I
have done for over 35 years. I cannot remember the last time I saw a
piece of kit of any description, which employed a positive ground. My
friend, who owns a computer repair shop, and has done for many years,
cannot remember the last time - if ever - that he saw a monitor with
an external power supply, that was not negative ground with the
connector sleeve as the negative connection.
With so much interconnectivity between household items now, there has
had to be a degree of standardisation on this issue, and it has
evolved through a general concensus amongst manufacturers, that
negative ground will be the convention.

As for your method of determining polarity, it makes no sense at all,
unless you are assuming a series diode, which is quite unlikely in
most modern kit, as it represents a waste of power due to its forward
voltage drop. It may even have a shunt protection diode, in which
case, your 'test' will ensure that the polarity is determined
INcorrectly. Even if the device did have a series diode, depending on
where the supply first goes, there is still no guarantee that there
will be any reading at all on a standard multimeter on ohms. If there
is not any diode - series or shunt - any reading of ohms obtained
across the input socket, is unlikely to reveal anything meaningful.
What is your experience in fault-finding, I wonder, to have caused
you to have formulated such a bizarre method, and believe that it
would uncategorically give you a correct result ?
Arfa

Actually being an electrical engineer for 35 years, I could careless how
long your friend has been repairing computers. And the reason why the ohm
meter works is because all of the curcuits are in parallel with the
supply. Thus you will get a lower reading when the polarity is correct.
And you will get a higher reading when it is not correct. Thus as all of
the circuits are reversed biased.

That is unmitigated nonsense. If there is a shunt protection diode, it will
be FORWARD biased when the polarity is WRONG. Also, the fact that my friend
repairs this stuff all day, and as an electrical engineer, you clearly do
not, that makes him an expert, compared to you ...


Whether or not all manufactures use negative ground or not, I have no
idea.

Well, as I repair this stuff all day as well, I *do* have an idea, so that
clearly also makes me more of an expert on this particular subject, than
you ...

Although in all of my experience, I have learned to never assume anything.
And I have seen many strange designs. One of them had an OP amp's output
connected directly to ground. I was confused about that one until I chatted
with the designer. Then it all made sense.

--
Bill

In general, I would agree with you not to assume anything, but some things
are a matter of convention, and in recent years, based on my direct
experience of such things, I would stick my neck on the line, and say that
this is one, and that all modern kit, manufactured for the domestic market,
employs circuitry with a negative ground, to which (most) external metalwork
is firmly bonded.

Arfa

Arfa Daily wrote:

snip

JHC !!! Do you not understand the word "modern" ? Do you not understand the
phrase "... deals with monitors of all types on a daily basis" ? I repair
this stuff all day every day for a living. I have done for over 35 years. I
cannot remember the last time I saw a piece of kit of any description, which
employed a positive ground. My friend, who owns a computer repair shop, and
has done for many years, cannot remember the last time - if ever - that he
saw a monitor with an external power supply, that was not negative ground
with the connector sleeve as the negative connection.

With so much interconnectivity between household items now, there has had to
be a degree of standardisation on this issue, and it has evolved through a
general concensus amongst manufacturers, that negative ground will be the
convention.

snip

I have resisted commenting but can do no longer; I don't know about the U.K.,
but I frequently encounter negative center coaxial power equipment in my
work. These are not monitors, but a variety of consumer and industrial
portable devices. When the connector is not labeled and I don't have docs,
I will physically inspect the internal wiring or the pcb that hosts the power
connector and also do resistance measurements between ground planes and the
power connector contacts to determine ground. The assumption that ground
planes are negative is a given in most instances. As for the subjective
label "modern", that is a religious issue that shouldn't be a factor in
good electronics practice

Michael

In ,
Michael A. Terrell typed on Sun, 30 Mar 2008 11:48:38 -0400:

I guess that no one bothered to check out the link I posted to a
replacement supply that not only shows it to be center positive, but
it tells you which coaxial power plug you need.

Yes we know Michael. And thanks again.

aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

Why do you say that? aioe is based in Italy.

--
Bill

In ,
Arfa Daily typed on Sun, 30 Mar 2008 16:24:25 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
[...]
As for a transistor radio that uses PNP transistors, I haven't
seen one that uses transistors at all for many years, let alone
PNP ones, so I think you might be struggling to fit that into my
"modern" category, also.

Well Arfa... they still use transistors (both NPN and PNP types)
in modern equipment. The reason you don't see them anymore is do
to the magic of minturization. But they are still there, just
neatly packaged into what is known today as the intergrated
circuit (IC chip).

And I though I was pedantic !! Yes, of course ICs contain
transistors, and yes, I would accept that some of them may be PNP
types, depending on block function within the IC, but I don't
think, with the best will in the world, that this is the level of
transistor existence that William was referring to with his
"transistor radio using PNP transistors" scenario. In any event,
in the case of an IC taking a single polarity rail, it is
irrelevant whether the transistors inside are NPN or PNP or FETs
or whatever. PNP transistors are just used 'upside down', as are
discrete PNP transistors when used in any piece of single
polarity rail equipment. The ground is still (typically for
//modern// equipment) the "-" side of the power supply / battery.
Anyway, this is getting out of hand. The OP aked a simple
question, and I gave a simple answer. This afternoon, I was in a
friend's computer repair shop. Bear in mind that he deals with
monitors of all types and makes on a daily basis. I asked him how
he would go about determining the polarity of such a monitor, and
he said that he would stick one side of his ohm meter on one of
the D connector locking screws, and the other on each pin of the
DC connector. When he found the pin that read short to the
connector locking screw, it was his contention that he would have
identified the "-" side of the power supply. So that's pretty
much exactly what I said. He also frowned and shook his head, and
said that he couldn't remember how many years it had been since
he had seen a DC connector that had the pin as the "-".
Which is also pretty much what I said ...

Arfa

That would be okay if it were a negative ground system. But like
what William Sommerwerck mentioned, we don't know that. The way I
would do it is to ohm the the power in. And the lower resistance
would be the correct polarity. Although you would need another
meter to read the polarity of the ohm meter. As they are not
standardized on multimeters. You could also use a diode (or LED)
to learn of the polarity of the meter as well. --
Bill

JHC !!! Do you not understand the word "modern" ? Do you not
understand the phrase "... deals with monitors of all types on a
daily basis" ? I repair this stuff all day every day for a living. I
have done for over 35 years. I cannot remember the last time I saw a
piece of kit of any description, which employed a positive ground.
My friend, who owns a computer repair shop, and has done for many
years, cannot remember the last time - if ever - that he saw a
monitor with an external power supply, that was not negative ground
with the connector sleeve as the negative connection.
With so much interconnectivity between household items now, there
has had to be a degree of standardisation on this issue, and it has
evolved through a general concensus amongst manufacturers, that
negative ground will be the convention.

As for your method of determining polarity, it makes no sense at
all, unless you are assuming a series diode, which is quite
unlikely in most modern kit, as it represents a waste of power due
to its forward voltage drop. It may even have a shunt protection
diode, in which case, your 'test' will ensure that the polarity is
determined INcorrectly. Even if the device did have a series diode,
depending on where the supply first goes, there is still no
guarantee that there will be any reading at all on a standard
multimeter on ohms. If there is not any diode - series or shunt -
any reading of ohms obtained across the input socket, is unlikely
to reveal anything meaningful. What is your experience in
fault-finding, I wonder, to have caused you to have formulated such
a bizarre method, and believe that it would uncategorically give
you a correct result ? Arfa

Actually being an electrical engineer for 35 years, I could careless
how long your friend has been repairing computers. And the reason
why the ohm meter works is because all of the curcuits are in
parallel with the supply. Thus you will get a lower reading when the
polarity is correct. And you will get a higher reading when it is
not correct. Thus as all of the circuits are reversed biased.

That is unmitigated nonsense. If there is a shunt protection diode,
it will be FORWARD biased when the polarity is WRONG. Also, the fact
that my friend repairs this stuff all day, and as an electrical
engineer, you clearly do not, that makes him an expert, compared to
you ...

If there was a shunt protection diode, then both resistance measurements
would be forward biased. Thus you would know that since there was no
high resistance reading. But let's assume and use your plan for a
minute. There are plenty of examples where they don't ground the shield
but just let it float. Yes it sounds stupid I know, but it has been done
from time to time. And I worry about everything seemingly coming from
China nowadays. Which IMHO is only going to make things worse. And some
of this stuff from China, isn't even UL or FCC approved.

Whether or not all manufactures use negative ground or not, I have no
idea.

Well, as I repair this stuff all day as well, I *do* have an idea, so
that clearly also makes me more of an expert on this particular
subject, than you ...

That is indeed possible. I always said and believed that we can learn a
lot even from a child.

Although in all of my experience, I have learned to never assume
anything. And I have seen many strange designs. One of them had an
OP amp's output connected directly to ground. I was confused about
that one until I chatted with the designer. Then it all made sense.
--
Bill

In general, I would agree with you not to assume anything, but some
things are a matter of convention, and in recent years, based on my
direct experience of such things, I would stick my neck on the line,
and say that this is one, and that all modern kit, manufactured for
the domestic market, employs circuitry with a negative ground, to
which (most) external metalwork is firmly bonded.

Arfa

I also have seen grounds that wasn't really ground either. Shields that
were not connected to anything. Lots of weird stuff goes on in consumer
grade equipment. Most of it IMHO is done to save a buck. Some of it is
just ingenious! And some of it is just sloppy engineering. And sometimes
it was done as a last minute bandaid just to pass FCC radio emissions.


--
Bill

Why do you say that? aioe is based in Italy.



It has nothing to do with where it's based. Apparently you missed the very
long thread about this a while back and the load of impostors trying to
raise hell spamming from aioe. Most of us blocked the server entirely.

In news:LQTHj.923$at6.237@trndny01,
James Sweet typed on Sun, 30 Mar 2008 21:44:11 GMT:
Why do you say that? aioe is based in Italy.

It has nothing to do with where it's based. Apparently you missed the
very long thread about this a while back and the load of impostors
trying to raise hell spamming from aioe. Most of us blocked the
server entirely.

Hi James! Oh yes I did miss that one. Thanks for the heads up.

--
Bill

"msg" wrote in message
...
Arfa Daily wrote:

snip

JHC !!! Do you not understand the word "modern" ? Do you not understand
the phrase "... deals with monitors of all types on a daily basis" ? I
repair this stuff all day every day for a living. I have done for over 35
years. I cannot remember the last time I saw a piece of kit of any
description, which employed a positive ground. My friend, who owns a
computer repair shop, and has done for many years, cannot remember the
last time - if ever - that he saw a monitor with an external power
supply, that was not negative ground with the connector sleeve as the
negative connection.

With so much interconnectivity between household items now, there has had
to be a degree of standardisation on this issue, and it has evolved
through a general concensus amongst manufacturers, that negative ground
will be the convention.

snip

I have resisted commenting but can do no longer; I don't know about the
U.K.,
but I frequently encounter negative center coaxial power equipment in my
work. These are not monitors, but a variety of consumer and industrial
portable devices. When the connector is not labeled and I don't have
docs,
I will physically inspect the internal wiring or the pcb that hosts the
power
connector and also do resistance measurements between ground planes and
the
power connector contacts to determine ground. The assumption that ground
planes are negative is a given in most instances. As for the subjective
label "modern", that is a religious issue that shouldn't be a factor in
good electronics practice

Michael

Michael. I'm not quite sure exactly what you are saying here. I do not doubt
that you encounter equipment with a negative pin connection on the coaxial
DC connector. I have not disputed this during this thread. In fact, I
actually said in my original reply to the OP, that although these days, pin
= "+" is the common convention, it is by no means cast in stone. I'm sure
that even though you do have dealings with negative pin equipment, you would
concede that positive pin is by far the more common at this point in time,
and has been for some years. Irrespective of which pole of the connector is
the positive one, you seem to accept that ground being negative is the "...
given in most instances", which is what most of the controversy generated
within the thread, has been about. So as far as I can see, we are both 'on
the same page'.

I don't understand what you are saying about the word "modern". It is quite
a well defined word, and fits well, in this context, with the dictionary
definition

http://dictionary.reference.com/browse/modern

particularly with the entry that refers to it being something that is "not
obsolete". Whilst you are correct that it is a subjective word, in the case
of electronic equipment, I would contend that most electronic engineers
would infer something of the order of 8 -10 years to be meant, when calling
electronic equipment "modern".

And Bill.

I will now explain why your contention that your method will work under all
circumstances, is not valid. You are quite wrong with your assumption that
all of the circuits in a piece of equipment are stacked up in parallel
across the DC input socket. Whilst this might have been the case some years
back, the DC connector on "modern" (infer whatever period you like from that
word) equipment, usually connects straight into some form of internal
ancilliary power supply, or a regulator or regulators, which are often
switching types.

The reasons for this are manifold, but include the fact that most modern
equipment does not contain circuitry that runs just from 12v, which is a
typical 'standard' value for external power unit equipment, and also
efficiency, which dictates the regulators typically being switchers. The
various circuits contained within the equipment, are connected to the back
end of these regulators, and are thus not connected to the DC power socket
in any way.

Often, the input to this regulator circuitry, contained within special
purpose ICs, will not produce any meaningful ohms reading, when subjected to
the low test voltage from a multimeter. So, you are just as likely to read a
virtual open circuit across the socket, irrespective of which way round you
have your meter. This, in itself, will not help you to determine the
polarity. But worse. If the unit employs a shunt protection diode, when your
meter is connected //backwards// to the correct polarity, you will get a
reading of 700 ohms or so, but when it is connected the //correct// way
round, you may well read infinity or near. By your definition of how your
system works to determine polarity, that would give you a clear indication
of which was the correct polarity, but would actually yield the *INcorrect*
polarity.

As for external metalwork not being connected to the internal common ground,
these days, that is rare. I do come across the situation sometimes, on AV
amps, where the RCA socket sleeves are floating with respect to the chassis,
but it is the exception rather than the rule, and is done to help alleviate
potential ground loop issues when connecting to other equipment.

As far as the polarity of the ground goes, I am prepared to say that in my
considerable experience, on modern equipment designed for the consumer
market, it is always negative. And that really is about as cast in stone as
anything in electronic design ever is. I could of course be wrong on this,
but if anyone wants to correct me with specific examples - remembering
"modern" and "domestic", I'm listening, and willing to modify my position on
it.

I say again, that the OP asked a simple question, to which there was a
simple answer. I don't really believe that there was any need to muddy the
waters to the extent of all of this silly stuff that has been put forward,
but hey - ho. I guess it all makes for an interesting life ... d;~}

Arfa

In ,
Arfa Daily typed on Mon, 31 Mar 2008 00:37:00 GMT:
[...]
And Bill.

I will now explain why your contention that your method will work
under all circumstances, is not valid.

Sorry if you got that impression, but that isn't what I meant.

You are quite wrong with your
assumption that all of the circuits in a piece of equipment are
stacked up in parallel across the DC input socket. Whilst this might
have been the case some years back, the DC connector on "modern"
(infer whatever period you like from that word) equipment, usually
connects straight into some form of internal ancilliary power supply,
or a regulator or regulators, which are often switching types.

Yes I remember.

The reasons for this are manifold, but include the fact that most
modern equipment does not contain circuitry that runs just from 12v,
which is a typical 'standard' value for external power unit
equipment, and also efficiency, which dictates the regulators
typically being switchers. The various circuits contained within the
equipment, are connected to the back end of these regulators, and are
thus not connected to the DC power socket in any way.

Yes but the regulators are.

Often, the input to this regulator circuitry, contained within special
purpose ICs, will not produce any meaningful ohms reading, when
subjected to the low test voltage from a multimeter. So, you are just
as likely to read a virtual open circuit across the socket,
irrespective of which way round you have your meter. This, in itself,
will not help you to determine the polarity.

Yes... so if you have a high/low resistance readings, this is very
useful. If you have a low/low or a high/high, checking the resistance
isn't useful under these conditions.

But worse. If the unit
employs a shunt protection diode, when your meter is connected
//backwards// to the correct polarity, you will get a reading of 700
ohms or so, but when it is connected the //correct// way round, you
may well read infinity or near. By your definition of how your system
works to determine polarity, that would give you a clear indication
of which was the correct polarity, but would actually yield the
*INcorrect* polarity.

True, but it will not hurt anything. As the shunt will only allow about
a negative 0.7v to the rest of the unit. So unless the shunt blows, it
shouldn't ever hurt it. You can possibly damage the adapter, but it
should be protected against such anyway. But it is cheaper than the unit
it is powering anyway. ;-)

As for external metalwork not being connected to the internal common
ground, these days, that is rare. I do come across the situation
sometimes, on AV amps, where the RCA socket sleeves are floating with
respect to the chassis, but it is the exception rather than the rule,
and is done to help alleviate potential ground loop issues when
connecting to other equipment.
As far as the polarity of the ground goes, I am prepared to say that
in my considerable experience, on modern equipment designed for the
consumer market, it is always negative. And that really is about as
cast in stone as anything in electronic design ever is. I could of
course be wrong on this, but if anyone wants to correct me with
specific examples - remembering "modern" and "domestic", I'm
listening, and willing to modify my position on it.

Yes I agree. But thinking that way, you may fry every positive ground
you come across. If that is an acceptable risk for you and others...
well what can I say? While some risks are acceptable to me, frying
something because you had the polarity wrong just isn't one of them. LOL

I say again, that the OP asked a simple question, to which there was a
simple answer. I don't really believe that there was any need to
muddy the waters to the extent of all of this silly stuff that has
been put forward, but hey - ho. I guess it all makes for an
interesting life ... d;~}

I believe having enough information to make a wise choice is far better
than bozos telling you that you have to do it this way and there are no
becauses.

--
Bill

"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Mon, 31 Mar 2008 00:37:00 GMT:
[...]
And Bill.

I will now explain why your contention that your method will work
under all circumstances, is not valid.

Sorry if you got that impression, but that isn't what I meant.

You are quite wrong with your
assumption that all of the circuits in a piece of equipment are
stacked up in parallel across the DC input socket. Whilst this might
have been the case some years back, the DC connector on "modern"
(infer whatever period you like from that word) equipment, usually
connects straight into some form of internal ancilliary power supply,
or a regulator or regulators, which are often switching types.

Yes I remember.

The reasons for this are manifold, but include the fact that most
modern equipment does not contain circuitry that runs just from 12v,
which is a typical 'standard' value for external power unit
equipment, and also efficiency, which dictates the regulators
typically being switchers. The various circuits contained within the
equipment, are connected to the back end of these regulators, and are
thus not connected to the DC power socket in any way.

Yes but the regulators are.

Often, the input to this regulator circuitry, contained within special
purpose ICs, will not produce any meaningful ohms reading, when
subjected to the low test voltage from a multimeter. So, you are just
as likely to read a virtual open circuit across the socket,
irrespective of which way round you have your meter. This, in itself,
will not help you to determine the polarity.

Yes... so if you have a high/low resistance readings, this is very useful.
If you have a low/low or a high/high, checking the resistance isn't useful
under these conditions.

But worse. If the unit
employs a shunt protection diode, when your meter is connected
//backwards// to the correct polarity, you will get a reading of 700
ohms or so, but when it is connected the //correct// way round, you
may well read infinity or near. By your definition of how your system
works to determine polarity, that would give you a clear indication
of which was the correct polarity, but would actually yield the
*INcorrect* polarity.

True, but it will not hurt anything. As the shunt will only allow about a
negative 0.7v to the rest of the unit. So unless the shunt blows, it
shouldn't ever hurt it. You can possibly damage the adapter, but it should
be protected against such anyway. But it is cheaper than the unit it is
powering anyway. ;-)

As for external metalwork not being connected to the internal common
ground, these days, that is rare. I do come across the situation
sometimes, on AV amps, where the RCA socket sleeves are floating with
respect to the chassis, but it is the exception rather than the rule,
and is done to help alleviate potential ground loop issues when
connecting to other equipment.
As far as the polarity of the ground goes, I am prepared to say that
in my considerable experience, on modern equipment designed for the
consumer market, it is always negative. And that really is about as
cast in stone as anything in electronic design ever is. I could of
course be wrong on this, but if anyone wants to correct me with
specific examples - remembering "modern" and "domestic", I'm
listening, and willing to modify my position on it.

Yes I agree. But thinking that way, you may fry every positive ground you
come across. If that is an acceptable risk for you and others... well what
can I say? While some risks are acceptable to me, frying something because
you had the polarity wrong just isn't one of them. LOL

I say again, that the OP asked a simple question, to which there was a
simple answer. I don't really believe that there was any need to
muddy the waters to the extent of all of this silly stuff that has
been put forward, but hey - ho. I guess it all makes for an
interesting life ... d;~}

I believe having enough information to make a wise choice is far better
than bozos telling you that you have to do it this way and there are no
becauses.

--
Bill

Well, I guess we could go on dancing around this one for ever ...

With the circuit loads being connected to the back end of regulators that
are likely to have high input resistances with respect to the low test
voltage supplied by a multimeter, you really are unlikely to read anything
meaningful across the DC input socket. Trust me. I do this (very
successfully) for a living. Reading high-low, low-low, high-high, is
fundamentally useless to determining input polarity, unless you have a
schematic for the equipment to know what you are looking at. If you had a
schematic, you would not, of course, be trying to determine the polarity in
the first place ...

It is also not necessarily true that you will damage nothing if you do
arrive at a wrong conclusion as a result of applying your ohm-meter test to
an equipment which employs a shunt protection diode. Remember that the power
supplies for LCD TV sets and monitors, when these are external types, are
capable of supplying typically 2 to 4 amps. This is plenty enough to destroy
a typical 1 amp shunt diode, or to blow a pico or surface mount fuse, as is
typically found in such devices, or even to take out print, which is
sometimes deliberately 'necked' to provide a fuse function. Shunt protection
diodes seldom survive a reverse connection. Ask anyone who repairs CB
radios, or PMR radios, or plain old car entertainment radios.

Even if no shunt diode is used, there is still no guarantee that any
regulator device which has reverse polarity applied to it, will survive. I
have seen plenty that haven't.

I honestly don't believe that I am going to fry *any* positive grounds that
I come across, for the simple reason that on modern equipment, I just don't
come across them. They died out pretty much with germanium PNP transistors.
Obviously, if I was trying to determine the polarity of a piece of 30 year
old kit, I would take the trouble to employ different methods to do so, on
the off-chance that it might have a positive ground, but again, trust me,
positive grounds simply *aren't* encountered on modern equipment.

I hope when you refer to "bozos", you are not including me in that, as it
would cause me to take extreme offence at you. Having enough information to
make a wise choice is indeed a laudable objective, but discounting the
advice of someone who has more than 35 years declared experience in a field,
borders on stupidity. I certainly would not tell anyone that they *must* do
it this way, but if I believe, based on my considerable experience in the
repair field, that a particular method is likely to yield a correct answer
with a better than 95% certainty, then I am going to advise them of this,
which I believe is the way I approached the OP's original question, in the
first place.

Whilst there are always "becauses" as you put it, in this particular case,
their validity is negligible, for all of the reasons that I have
(painstakingly) explained over and over.

Arfa

Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from ebay.
It didn't have a power cord. It says it's a 12v dc 2.5a but it doesn't
give the polarity. A person from gateway said he thought it wouldn't hurt
the monitor if it got plugged in backwards but I'd rather not try it.

Would appreciate any help.

If it has got any external metal parts such as RCA (phono) connector outers,
BNC connector outers, 'D' connector surround etc, or possibly screws for a
stand, as these often go right through the plastic case, and into the
internal chassis, then try measuring from any such metal to each of the DC
power input connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground ( "-" )
connection. The other will then be the "+". Assuming that it's a 'standard'
co-axial DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you are
obtaining a replacement PSU, that the plug is often a slightly abnormal
size, being a little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the job, as these
monitors do draw quite a lot of current, and may well surge up close to the
quoted 2.5 amps at startup, as the LCD backlights first fire up before
settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like to
say. Some equipment is perfectly well protected against such 'consumer
antics', but it is by no means guaranteed, and if it is not adequately
protected, the result is often an item that's fried beyond repair, for no
other reason than unobtainable power supply devices, as many previous posts
on this subject over the years, will attest ...

Arfa



The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.

In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from ebay.
It didn't have a power cord. It says it's a 12v dc 2.5a but it doesn't
give the polarity. A person from gateway said he thought it wouldn't hurt
the monitor if it got plugged in backwards but I'd rather not try it.

Would appreciate any help.

If it has got any external metal parts such as RCA (phono) connector outers,
BNC connector outers, 'D' connector surround etc, or possibly screws for a
stand, as these often go right through the plastic case, and into the
internal chassis, then try measuring from any such metal to each of the DC
power input connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground ( "-" )
connection. The other will then be the "+". Assuming that it's a 'standard'
co-axial DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you are
obtaining a replacement PSU, that the plug is often a slightly abnormal
size, being a little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the job, as these
monitors do draw quite a lot of current, and may well surge up close to the
quoted 2.5 amps at startup, as the LCD backlights first fire up before
settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like to
say. Some equipment is perfectly well protected against such 'consumer
antics', but it is by no means guaranteed, and if it is not adequately
protected, the result is often an item that's fried beyond repair, for no
other reason than unobtainable power supply devices, as many previous posts
on this subject over the years, will attest ...

Arfa



The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.


Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from ebay.
It didn't have a power cord. It says it's a 12v dc 2.5a but it doesn't
give the polarity. A person from gateway said he thought it wouldn't hurt
the monitor if it got plugged in backwards but I'd rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector outers,
BNC connector outers, 'D' connector surround etc, or possibly screws for a
stand, as these often go right through the plastic case, and into the
internal chassis, then try measuring from any such metal to each of the DC
power input connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground ( "-" )
connection. The other will then be the "+". Assuming that it's a 'standard'
co-axial DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you are
obtaining a replacement PSU, that the plug is often a slightly abnormal
size, being a little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the job, as these
monitors do draw quite a lot of current, and may well surge up close to the
quoted 2.5 amps at startup, as the LCD backlights first fire up before
settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like to
say. Some equipment is perfectly well protected against such 'consumer
antics', but it is by no means guaranteed, and if it is not adequately
protected, the result is often an item that's fried beyond repair, for no
other reason than unobtainable power supply devices, as many previous posts
on this subject over the years, will attest ...

Arfa


The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.


Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.

"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd
rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or possibly
screws for a stand, as these often go right through the plastic case,
and into the internal chassis, then try measuring from any such metal
to each of the DC power input connector's terminals in turn, using an
ohm meter. Chances are you'll find a direct connection, and that will
be your DC ground ( "-" ) connection. The other will then be the "+".
Assuming that it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's not
cast in stone. Be aware when you are obtaining a replacement PSU, that
the plug is often a slightly abnormal size, being a little larger than
those you typically find on 'general' power supplies. Also, make sure
that you get one well rated for the job, as these monitors do draw
quite a lot of current, and may well surge up close to the quoted 2.5
amps at startup, as the LCD backlights first fire up before settling to
their run current.

As to whether it would be safe to reverse connect it, I wouldn't like
to say. Some equipment is perfectly well protected against such
'consumer antics', but it is by no means guaranteed, and if it is not
adequately protected, the result is often an item that's fried beyond
repair, for no other reason than unobtainable power supply devices, as
many previous posts on this subject over the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no
resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.


Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

The adapter symbol shows center + and side -. It is labeled 12vdc 4a. The
monitor is 12vdc 2.5a so the adapter should have enough power.

Before condemning the monitor, I would feel inclined to just try a different
power supply (bearing in mind that the one you are using now is not an
'original'). The reason that I say this is that there can be quite a high
initial pulse of current demand, as the backlights strike, and it just might
be that the power supply sags a little when hit with this, even though it
*says* that it is rated for 4A ...

Arfa

"Arfa Daily" wrote in message
...

"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd
rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or possibly
screws for a stand, as these often go right through the plastic case,
and into the internal chassis, then try measuring from any such metal
to each of the DC power input connector's terminals in turn, using an
ohm meter. Chances are you'll find a direct connection, and that will
be your DC ground ( "-" ) connection. The other will then be the "+".
Assuming that it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's not
cast in stone. Be aware when you are obtaining a replacement PSU, that
the plug is often a slightly abnormal size, being a little larger than
those you typically find on 'general' power supplies. Also, make sure
that you get one well rated for the job, as these monitors do draw
quite a lot of current, and may well surge up close to the quoted 2.5
amps at startup, as the LCD backlights first fire up before settling
to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like
to say. Some equipment is perfectly well protected against such
'consumer antics', but it is by no means guaranteed, and if it is not
adequately protected, the result is often an item that's fried beyond
repair, for no other reason than unobtainable power supply devices, as
many previous posts on this subject over the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no
resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair
it or just return it.


Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.

Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using now is
not an 'original'). The reason that I say this is that there can be quite
a high initial pulse of current demand, as the backlights strike, and it
just might be that the power supply sags a little when hit with this, even
though it *says* that it is rated for 4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ? LCD
monitors, like their CRT counterparts in many cases, don't just 'idle' when
there is no signal. They do just like you say - that is power up long enough
to check if they can detect an input signal, and if they can't, go back to
an inert condition.

Arfa

Arfa Daily wrote:
"Arfa Daily" wrote in message
...
"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
doesn't give the polarity. A person from gateway said he thought it
wouldn't hurt the monitor if it got plugged in backwards but I'd
rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or possibly
screws for a stand, as these often go right through the plastic case,
and into the internal chassis, then try measuring from any such metal
to each of the DC power input connector's terminals in turn, using an
ohm meter. Chances are you'll find a direct connection, and that will
be your DC ground ( "-" ) connection. The other will then be the "+".
Assuming that it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's not
cast in stone. Be aware when you are obtaining a replacement PSU, that
the plug is often a slightly abnormal size, being a little larger than
those you typically find on 'general' power supplies. Also, make sure
that you get one well rated for the job, as these monitors do draw
quite a lot of current, and may well surge up close to the quoted 2.5
amps at startup, as the LCD backlights first fire up before settling
to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like
to say. Some equipment is perfectly well protected against such
'consumer antics', but it is by no means guaranteed, and if it is not
adequately protected, the result is often an item that's fried beyond
repair, for no other reason than unobtainable power supply devices, as
many previous posts on this subject over the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no
resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair
it or just return it.

Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -
The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.
Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using now is
not an 'original'). The reason that I say this is that there can be quite
a high initial pulse of current demand, as the backlights strike, and it
just might be that the power supply sags a little when hit with this, even
though it *says* that it is rated for 4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ? LCD
monitors, like their CRT counterparts in many cases, don't just 'idle' when
there is no signal. They do just like you say - that is power up long enough
to check if they can detect an input signal, and if they can't, go back to
an inert condition.

Arfa



I tried it in a few different conditions: with the monitor on 1st and
then the computer - it showed the computer booting for a few seconds and
then went black - then it came on again after the boot was finished for
a few seconds and then went black again; with the computer on and then
the monitor; with the monitor disconnected from the computer (the manual
says it's supposed to bring up a diagnostic screen in this condition but
it didn't). The screen stayed black the whole time in subsequent attempts.

The power led would go from yellow to green when the computer started
booting but the screen stayed black.

I also noticed that the screen was not completely flush in the housing -
like someone had tried to, or did, open it and didn't close it completely.

"zirath" wrote in message
news:M_FLj.6004$PJ3.1496@trndny02...
Arfa Daily wrote:
"Arfa Daily" wrote in message
...
"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but
it doesn't give the polarity. A person from gateway said he thought
it wouldn't hurt the monitor if it got plugged in backwards but I'd
rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or
possibly screws for a stand, as these often go right through the
plastic case, and into the internal chassis, then try measuring from
any such metal to each of the DC power input connector's terminals
in turn, using an ohm meter. Chances are you'll find a direct
connection, and that will be your DC ground ( "-" ) connection. The
other will then be the "+". Assuming that it's a 'standard' co-axial
DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you
are obtaining a replacement PSU, that the plug is often a slightly
abnormal size, being a little larger than those you typically find
on 'general' power supplies. Also, make sure that you get one well
rated for the job, as these monitors do draw quite a lot of current,
and may well surge up close to the quoted 2.5 amps at startup, as
the LCD backlights first fire up before settling to their run
current.

As to whether it would be safe to reverse connect it, I wouldn't
like to say. Some equipment is perfectly well protected against such
'consumer antics', but it is by no means guaranteed, and if it is
not adequately protected, the result is often an item that's fried
beyond repair, for no other reason than unobtainable power supply
devices, as many previous posts on this subject over the years, will
attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no
resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair
it or just return it.

Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the
adaptor cannot start the monitor because it is not powerful enough, it
will sometimes just flash the backlight then go off.

- Tim -
The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.
Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using now
is not an 'original'). The reason that I say this is that there can be
quite a high initial pulse of current demand, as the backlights strike,
and it just might be that the power supply sags a little when hit with
this, even though it *says* that it is rated for 4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ? LCD
monitors, like their CRT counterparts in many cases, don't just 'idle'
when there is no signal. They do just like you say - that is power up
long enough to check if they can detect an input signal, and if they
can't, go back to an inert condition.

Arfa

I tried it in a few different conditions: with the monitor on 1st and then
the computer - it showed the computer booting for a few seconds and then
went black - then it came on again after the boot was finished for a few
seconds and then went black again; with the computer on and then the
monitor; with the monitor disconnected from the computer (the manual says
it's supposed to bring up a diagnostic screen in this condition but it
didn't). The screen stayed black the whole time in subsequent attempts.

The power led would go from yellow to green when the computer started
booting but the screen stayed black.

I also noticed that the screen was not completely flush in the housing -
like someone had tried to, or did, open it and didn't close it completely.

The fact that the light stays green, is a good sign. What you next need to
do, is to shine a strong desklamp or hand flashlamp at the screen at an
angle, after it has gone back to black. If you can then see an image on the
screen, that indicates that the backlamp tubes are not staying alight. This
could well be because either the inverter is faulty, or that a worn tube is
making the inverter shut down. Either is quite a common fault condition.

Arfa

Arfa Daily wrote:
"zirath" wrote in message
news:M_FLj.6004$PJ3.1496@trndny02...
Arfa Daily wrote:
"Arfa Daily" wrote in message
...
"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but
it doesn't give the polarity. A person from gateway said he thought
it wouldn't hurt the monitor if it got plugged in backwards but I'd
rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector
outers, BNC connector outers, 'D' connector surround etc, or
possibly screws for a stand, as these often go right through the
plastic case, and into the internal chassis, then try measuring from
any such metal to each of the DC power input connector's terminals
in turn, using an ohm meter. Chances are you'll find a direct
connection, and that will be your DC ground ( "-" ) connection. The
other will then be the "+". Assuming that it's a 'standard' co-axial
DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you
are obtaining a replacement PSU, that the plug is often a slightly
abnormal size, being a little larger than those you typically find
on 'general' power supplies. Also, make sure that you get one well
rated for the job, as these monitors do draw quite a lot of current,
and may well surge up close to the quoted 2.5 amps at startup, as
the LCD backlights first fire up before settling to their run
current.

As to whether it would be safe to reverse connect it, I wouldn't
like to say. Some equipment is perfectly well protected against such
'consumer antics', but it is by no means guaranteed, and if it is
not adequately protected, the result is often an item that's fried
beyond repair, for no other reason than unobtainable power supply
devices, as many previous posts on this subject over the years, will
attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no
resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair
it or just return it.

Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the
adaptor cannot start the monitor because it is not powerful enough, it
will sometimes just flash the backlight then go off.

- Tim -
The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.
Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using now
is not an 'original'). The reason that I say this is that there can be
quite a high initial pulse of current demand, as the backlights strike,
and it just might be that the power supply sags a little when hit with
this, even though it *says* that it is rated for 4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ? LCD
monitors, like their CRT counterparts in many cases, don't just 'idle'
when there is no signal. They do just like you say - that is power up
long enough to check if they can detect an input signal, and if they
can't, go back to an inert condition.

Arfa
I tried it in a few different conditions: with the monitor on 1st and then
the computer - it showed the computer booting for a few seconds and then
went black - then it came on again after the boot was finished for a few
seconds and then went black again; with the computer on and then the
monitor; with the monitor disconnected from the computer (the manual says
it's supposed to bring up a diagnostic screen in this condition but it
didn't). The screen stayed black the whole time in subsequent attempts.

The power led would go from yellow to green when the computer started
booting but the screen stayed black.

I also noticed that the screen was not completely flush in the housing -
like someone had tried to, or did, open it and didn't close it completely.

The fact that the light stays green, is a good sign. What you next need to
do, is to shine a strong desklamp or hand flashlamp at the screen at an
angle, after it has gone back to black. If you can then see an image on the
screen, that indicates that the backlamp tubes are not staying alight. This
could well be because either the inverter is faulty, or that a worn tube is
making the inverter shut down. Either is quite a common fault condition.

Arfa



I was able to see the image on the screen - but the monitor remained
black the whole time (it didn't go back to black).

zirath wrote:
Arfa Daily wrote:
"zirath" wrote in message
news:M_FLj.6004$PJ3.1496@trndny02...
Arfa Daily wrote:
"Arfa Daily" wrote in message
...
"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09,
says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor
from ebay. It didn't have a power cord. It says it's a 12v dc
2.5a but it doesn't give the polarity. A person from gateway
said he thought it wouldn't hurt the monitor if it got plugged
in backwards but I'd rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono)
connector outers, BNC connector outers, 'D' connector surround
etc, or possibly screws for a stand, as these often go right
through the plastic case, and into the internal chassis, then
try measuring from any such metal to each of the DC power input
connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC
ground ( "-" ) connection. The other will then be the "+".
Assuming that it's a 'standard' co-axial DC connector, on most
modern equipment, 'pin' is "+" and side contact is "-" although
that's not cast in stone. Be aware when you are obtaining a
replacement PSU, that the plug is often a slightly abnormal
size, being a little larger than those you typically find on
'general' power supplies. Also, make sure that you get one well
rated for the job, as these monitors do draw quite a lot of
current, and may well surge up close to the quoted 2.5 amps at
startup, as the LCD backlights first fire up before settling to
their run current.

As to whether it would be safe to reverse connect it, I
wouldn't like to say. Some equipment is perfectly well
protected against such 'consumer antics', but it is by no means
guaranteed, and if it is not adequately protected, the result
is often an item that's fried beyond repair, for no other
reason than unobtainable power supply devices, as many previous
posts on this subject over the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center
pin (it went to 0 and then back towards the center). The side
showed no resistance.

The monitor went on briefly and then went black when plugged
into the power. Seems like it's a dud. Not sure if it's worth
trying to repair it or just return it.

Is there no little pic of the connector around where it give the
info about power? Usually there is a universal icon used that
indicates polarity, kinda like a big C around a dot. Most, but
not all, coaxial power connectors have the minus side on the
outside, that way if it touches a grounded side, it will not
destroy the adapter. If the adaptor cannot start the monitor
because it is not powerful enough, it will sometimes just flash
the backlight then go off.

- Tim -
The adapter symbol shows center + and side -. It is labeled 12vdc
4a. The monitor is 12vdc 2.5a so the adapter should have enough
power.
Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using
now is not an 'original'). The reason that I say this is that there
can be quite a high initial pulse of current demand, as the
backlights strike, and it just might be that the power supply sags
a little when hit with this, even though it *says* that it is rated
for 4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ?
LCD monitors, like their CRT counterparts in many cases, don't just
'idle' when there is no signal. They do just like you say - that is
power up long enough to check if they can detect an input signal,
and if they can't, go back to an inert condition.

Arfa
I tried it in a few different conditions: with the monitor on 1st and
then the computer - it showed the computer booting for a few seconds
and then went black - then it came on again after the boot was
finished for a few seconds and then went black again; with the
computer on and then the monitor; with the monitor disconnected from
the computer (the manual says it's supposed to bring up a diagnostic
screen in this condition but it didn't). The screen stayed black the
whole time in subsequent attempts.

The power led would go from yellow to green when the computer started
booting but the screen stayed black.

I also noticed that the screen was not completely flush in the
housing - like someone had tried to, or did, open it and didn't close
it completely.

The fact that the light stays green, is a good sign. What you next
need to do, is to shine a strong desklamp or hand flashlamp at the
screen at an angle, after it has gone back to black. If you can then
see an image on the screen, that indicates that the backlamp tubes are
not staying alight. This could well be because either the inverter is
faulty, or that a worn tube is making the inverter shut down. Either
is quite a common fault condition.

Arfa


I was able to see the image on the screen - but the monitor remained
black the whole time (it didn't go back to black).

(I shined a bright light on the monitor at an angle).

"zirath" wrote in message
news:US_Lj.727$HJ1.200@trndny01...
zirath wrote:
Arfa Daily wrote:
"zirath" wrote in message
news:M_FLj.6004$PJ3.1496@trndny02...
Arfa Daily wrote:
"Arfa Daily" wrote in message
...
"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09,
says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor
from ebay. It didn't have a power cord. It says it's a 12v dc
2.5a but it doesn't give the polarity. A person from gateway
said he thought it wouldn't hurt the monitor if it got plugged
in backwards but I'd rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono)
connector outers, BNC connector outers, 'D' connector surround
etc, or possibly screws for a stand, as these often go right
through the plastic case, and into the internal chassis, then try
measuring from any such metal to each of the DC power input
connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground
( "-" ) connection. The other will then be the "+". Assuming that
it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's
not cast in stone. Be aware when you are obtaining a replacement
PSU, that the plug is often a slightly abnormal size, being a
little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the
job, as these monitors do draw quite a lot of current, and may
well surge up close to the quoted 2.5 amps at startup, as the LCD
backlights first fire up before settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't
like to say. Some equipment is perfectly well protected against
such 'consumer antics', but it is by no means guaranteed, and if
it is not adequately protected, the result is often an item
that's fried beyond repair, for no other reason than unobtainable
power supply devices, as many previous posts on this subject over
the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin
(it went to 0 and then back towards the center). The side showed
no resistance.

The monitor went on briefly and then went black when plugged into
the power. Seems like it's a dud. Not sure if it's worth trying to
repair it or just return it.

Is there no little pic of the connector around where it give the
info about power? Usually there is a universal icon used that
indicates polarity, kinda like a big C around a dot. Most, but not
all, coaxial power connectors have the minus side on the outside,
that way if it touches a grounded side, it will not destroy the
adapter. If the adaptor cannot start the monitor because it is not
powerful enough, it will sometimes just flash the backlight then go
off.

- Tim -
The adapter symbol shows center + and side -. It is labeled 12vdc
4a. The monitor is 12vdc 2.5a so the adapter should have enough
power.
Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using
now is not an 'original'). The reason that I say this is that there
can be quite a high initial pulse of current demand, as the
backlights strike, and it just might be that the power supply sags a
little when hit with this, even though it *says* that it is rated for
4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ?
LCD monitors, like their CRT counterparts in many cases, don't just
'idle' when there is no signal. They do just like you say - that is
power up long enough to check if they can detect an input signal, and
if they can't, go back to an inert condition.

Arfa
I tried it in a few different conditions: with the monitor on 1st and
then the computer - it showed the computer booting for a few seconds
and then went black - then it came on again after the boot was finished
for a few seconds and then went black again; with the computer on and
then the monitor; with the monitor disconnected from the computer (the
manual says it's supposed to bring up a diagnostic screen in this
condition but it didn't). The screen stayed black the whole time in
subsequent attempts.

The power led would go from yellow to green when the computer started
booting but the screen stayed black.

I also noticed that the screen was not completely flush in the
housing - like someone had tried to, or did, open it and didn't close
it completely.

The fact that the light stays green, is a good sign. What you next need
to do, is to shine a strong desklamp or hand flashlamp at the screen at
an angle, after it has gone back to black. If you can then see an image
on the screen, that indicates that the backlamp tubes are not staying
alight. This could well be because either the inverter is faulty, or
that a worn tube is making the inverter shut down. Either is quite a
common fault condition.

Arfa


I was able to see the image on the screen - but the monitor remained
black the whole time (it didn't go back to black).

(I shined a bright light on the monitor at an angle).

OK. Well that tells us that the whole monitor part is working, and the
failure is in the LCD screen backlighting circuit. It is generally a bit
fiddly, but it is repairable if you are that way inclined. Unless you are
able (or want to) just throw it back where you got it from.

Arfa

Arfa Daily wrote:
"zirath" wrote in message
news:US_Lj.727$HJ1.200@trndny01...
zirath wrote:
Arfa Daily wrote:
"zirath" wrote in message
news:M_FLj.6004$PJ3.1496@trndny02...
Arfa Daily wrote:
"Arfa Daily" wrote in message
...
"zirath" wrote in message
news:OAwLj.5472$XC1.1103@trndny08...
Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09,
says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor
from ebay. It didn't have a power cord. It says it's a 12v dc
2.5a but it doesn't give the polarity. A person from gateway
said he thought it wouldn't hurt the monitor if it got plugged
in backwards but I'd rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono)
connector outers, BNC connector outers, 'D' connector surround
etc, or possibly screws for a stand, as these often go right
through the plastic case, and into the internal chassis, then try
measuring from any such metal to each of the DC power input
connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground
( "-" ) connection. The other will then be the "+". Assuming that
it's a 'standard' co-axial DC connector, on most modern
equipment, 'pin' is "+" and side contact is "-" although that's
not cast in stone. Be aware when you are obtaining a replacement
PSU, that the plug is often a slightly abnormal size, being a
little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the
job, as these monitors do draw quite a lot of current, and may
well surge up close to the quoted 2.5 amps at startup, as the LCD
backlights first fire up before settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't
like to say. Some equipment is perfectly well protected against
such 'consumer antics', but it is by no means guaranteed, and if
it is not adequately protected, the result is often an item
that's fried beyond repair, for no other reason than unobtainable
power supply devices, as many previous posts on this subject over
the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin
(it went to 0 and then back towards the center). The side showed
no resistance.

The monitor went on briefly and then went black when plugged into
the power. Seems like it's a dud. Not sure if it's worth trying to
repair it or just return it.

Is there no little pic of the connector around where it give the
info about power? Usually there is a universal icon used that
indicates polarity, kinda like a big C around a dot. Most, but not
all, coaxial power connectors have the minus side on the outside,
that way if it touches a grounded side, it will not destroy the
adapter. If the adaptor cannot start the monitor because it is not
powerful enough, it will sometimes just flash the backlight then go
off.

- Tim -
The adapter symbol shows center + and side -. It is labeled 12vdc
4a. The monitor is 12vdc 2.5a so the adapter should have enough
power.
Before condemning the monitor, I would feel inclined to just try a
different power supply (bearing in mind that the one you are using
now is not an 'original'). The reason that I say this is that there
can be quite a high initial pulse of current demand, as the
backlights strike, and it just might be that the power supply sags a
little when hit with this, even though it *says* that it is rated for
4A ...

Arfa

Thinking about it again, were you trying it with a signal going in ?
LCD monitors, like their CRT counterparts in many cases, don't just
'idle' when there is no signal. They do just like you say - that is
power up long enough to check if they can detect an input signal, and
if they can't, go back to an inert condition.

Arfa
I tried it in a few different conditions: with the monitor on 1st and
then the computer - it showed the computer booting for a few seconds
and then went black - then it came on again after the boot was finished
for a few seconds and then went black again; with the computer on and
then the monitor; with the monitor disconnected from the computer (the
manual says it's supposed to bring up a diagnostic screen in this
condition but it didn't). The screen stayed black the whole time in
subsequent attempts.

The power led would go from yellow to green when the computer started
booting but the screen stayed black.

I also noticed that the screen was not completely flush in the
housing - like someone had tried to, or did, open it and didn't close
it completely.
The fact that the light stays green, is a good sign. What you next need
to do, is to shine a strong desklamp or hand flashlamp at the screen at
an angle, after it has gone back to black. If you can then see an image
on the screen, that indicates that the backlamp tubes are not staying
alight. This could well be because either the inverter is faulty, or
that a worn tube is making the inverter shut down. Either is quite a
common fault condition.

Arfa

I was able to see the image on the screen - but the monitor remained
black the whole time (it didn't go back to black).
(I shined a bright light on the monitor at an angle).

OK. Well that tells us that the whole monitor part is working, and the
failure is in the LCD screen backlighting circuit. It is generally a bit
fiddly, but it is repairable if you are that way inclined. Unless you are
able (or want to) just throw it back where you got it from.

Arfa



I'm into trying to repair it.

Is there info somewhere on how to do it?

Thanks for your help.

The fact that the light stays green, is a good sign. What you next
need to do, is to shine a strong desklamp or hand flashlamp at the
screen at an angle, after it has gone back to black. If you can then
see an image on the screen, that indicates that the backlamp tubes are
not staying alight. This could well be because either the inverter is
faulty, or that a worn tube is making the inverter shut down. Either
is quite a common fault condition.

Arfa

I was able to see the image on the screen - but the monitor remained
black the whole time (it didn't go back to black).
(I shined a bright light on the monitor at an angle).

OK. Well that tells us that the whole monitor part is working, and the
failure is in the LCD screen backlighting circuit. It is generally a bit
fiddly, but it is repairable if you are that way inclined. Unless you are
able (or want to) just throw it back where you got it from.

Arfa

I'm into trying to repair it.

Is there info somewhere on how to do it?

Thanks for your help.

If the screen comes apart easily, start by examining the backlight tubes. Be
careful when extracting them as they are quite fragile. If any are badly
blackened at the ends, suspect them. It's hard to test the inverter, without
having known good tubes to connect to it. If you have a 'scope, you can get
a good idea by looking to see if you have waveform at the primaries of each
of the tube high voltage drive transformers. If you do get a momentary burst
that then disappears, this could be because the inverter is detecting a bad
tube, and shutting down. You might see the tubes initially flash up, and you
might see one not do so. You can disconnect the tubes one at a time, and see
if that keeps the inverter running, and if it does, you can cross connect
the tubes to the opposite inverter outputs, to prove the drive electronics.
Inverters and tubes are available from a number of sources. See, for
instance,

http://www.lcdparts.net/ccfl.aspx

http://www.ergpower.com/pdf30/cross.pdf

http://www.ergpower.com/

Arfa

Arfa Daily wrote:
The fact that the light stays green, is a good sign. What you next
need to do, is to shine a strong desklamp or hand flashlamp at the
screen at an angle, after it has gone back to black. If you can then
see an image on the screen, that indicates that the backlamp tubes are
not staying alight. This could well be because either the inverter is
faulty, or that a worn tube is making the inverter shut down. Either
is quite a common fault condition.

Arfa

I was able to see the image on the screen - but the monitor remained
black the whole time (it didn't go back to black).
(I shined a bright light on the monitor at an angle).
OK. Well that tells us that the whole monitor part is working, and the
failure is in the LCD screen backlighting circuit. It is generally a bit
fiddly, but it is repairable if you are that way inclined. Unless you are
able (or want to) just throw it back where you got it from.

Arfa
I'm into trying to repair it.

Is there info somewhere on how to do it?

Thanks for your help.

If the screen comes apart easily, start by examining the backlight tubes. Be
careful when extracting them as they are quite fragile. If any are badly
blackened at the ends, suspect them. It's hard to test the inverter, without
having known good tubes to connect to it. If you have a 'scope, you can get
a good idea by looking to see if you have waveform at the primaries of each
of the tube high voltage drive transformers. If you do get a momentary burst
that then disappears, this could be because the inverter is detecting a bad
tube, and shutting down. You might see the tubes initially flash up, and you
might see one not do so. You can disconnect the tubes one at a time, and see
if that keeps the inverter running, and if it does, you can cross connect
the tubes to the opposite inverter outputs, to prove the drive electronics.
Inverters and tubes are available from a number of sources. See, for
instance,

http://www.lcdparts.net/ccfl.aspx

http://www.ergpower.com/pdf30/cross.pdf

http://www.ergpower.com/

Arfa



One thing I started wondering about after you were saying it could be a
problem with the adapter--

The picture of the original adapter that came with the monitor says the
plug is supposed to be 6.5mm o.d. 4.4mm i.d. and 9.5mm long. (Thanks to
Michael Terrell - http://www.lcdpayless.com/productpag...productId=237).

The measurements of the plug that came with the adapter I got (from
ebay) are : 5.5x2.5 / 9.5mm.

Could this be the problem?