[This followup was posted to sci.electronics.repair and a copy was sent to the cited author.]


I am repairing an LCD monitor that has the very common turn on problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

Michael Karas wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent to
the cited author.]


I am repairing an LCD monitor that has the very common turn on problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com


Is there a "bleed-through" route for start-up?

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here. This unit came to
me as a freeby already taken apart and the report that "It does not turn
on". So I just dived in with the power supply capacitor replacement
since that has worked many many times on other monitors (~ 15 so far). I
noticed that the particular transistor in question has discolored leads
and solder joints and the PC board has turned to a darker color than
normal.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

Michael Karas wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here. This unit came to
me as a freeby already taken apart and the report that "It does not turn
on". So I just dived in with the power supply capacitor replacement
since that has worked many many times on other monitors (~ 15 so far). I
noticed that the particular transistor in question has discolored leads
and solder joints and the PC board has turned to a darker color than
normal.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

You need to identify the supervisor IC and get its pinout hopefully.

Michael Karas schrieb:
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here. ...

This

http://www.bilder-hochladen.net/files/big/12b4-a6-6c52.jpg

is a typical schematic for a SMPS. The supply voltage for the
controlling IC is provided via R1 for the first moment - I think this
is N_Cook's "bleed-through" route. When the circuit is working the
supply voltage is generated by W3/D1/C6.

If R1 is open and/or C6 has a short the SMPS won't start.

HTH

Reinhard

"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here.

Its common practice for the SMPSU control chip Vcc to come from an extra
winding on the chopper transformer. Before the PSU starts up - there has to
be some source of Vcc to get it kick started.

Very often there's a high resistance resistor (or 2 in series) from the +ve
of the mains bridge to provide the initial start up supply for the control
chip - these resistors are very prone to going high/OC.

On Fri, 24 May 2013 06:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent to the cited author.]


I am repairing an LCD monitor that has the very common turn on problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?
Google 'marking code DFRG' and see if anything makes sense. Also, SMT
is a very generic term. If we knew the specific package, it would
help us help you.

Another resource, especially whre power supplies for LCD monitors are
concerned is www,badcaps.net/forum. Pictures help.

PlainBill

"Ian Field" wrote in message
...


"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here.

Its common practice for the SMPSU control chip Vcc to come from an extra
winding on the chopper transformer. Before the PSU starts up - there has
to be some source of Vcc to get it kick started.

Very often there's a high resistance resistor (or 2 in series) from the
+ve of the mains bridge to provide the initial start up supply for the
control chip - these resistors are very prone to going high/OC.


+1

And the cap in the C6 position on Reinhard's schematic is the one component
that I change more of on every design of switcher that I work on, than any
other component for no or intermittent start up. As the startup resistor is
such a high value, that cap has to be in near-perfect condition to buffer
that startup supply down to a low impedance for the control chip, until the
supply gets going, and the low impedance maintenance supply takes over. An
ESR meter is your friend here ...

Arfa

"Arfa Daily" wrote in message
...


"Ian Field" wrote in message
...


"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here.

Its common practice for the SMPSU control chip Vcc to come from an extra
winding on the chopper transformer. Before the PSU starts up - there has
to be some source of Vcc to get it kick started.

Very often there's a high resistance resistor (or 2 in series) from the
+ve of the mains bridge to provide the initial start up supply for the
control chip - these resistors are very prone to going high/OC.


+1

And the cap in the C6 position on Reinhard's schematic is the one
component that I change more of on every design of switcher that I work
on, than any other component for no or intermittent start up. As the
startup resistor is such a high value, that cap has to be in near-perfect
condition to buffer that startup supply down to a low impedance for the
control chip, until the supply gets going, and the low impedance
maintenance supply takes over. An ESR meter is your friend here ...

I don't have that particular schematic, but in general terms such capacitors
are usually quite small ( 1 - 47uF) such values are easy to get hold of in
multilayer ceramic chip capacitors - and the electrolyte will never dry out.

Ian Field schrieb:

"Arfa Daily" wrote in message

[...]
And the cap in the C6 position on Reinhard's schematic ...

I don't have that particular schematic, ...

Hmm, can't you see my posting as of May 24 with the link to that
schematic?

Wondering

Reinhard

Ian Field wrote in message
...


"Arfa Daily" wrote in message
...


"Ian Field" wrote in message
...


"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was
sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here.

Its common practice for the SMPSU control chip Vcc to come from an
extra
winding on the chopper transformer. Before the PSU starts up - there
has
to be some source of Vcc to get it kick started.

Very often there's a high resistance resistor (or 2 in series) from the
+ve of the mains bridge to provide the initial start up supply for the
control chip - these resistors are very prone to going high/OC.


+1

And the cap in the C6 position on Reinhard's schematic is the one
component that I change more of on every design of switcher that I work
on, than any other component for no or intermittent start up. As the
startup resistor is such a high value, that cap has to be in
near-perfect
condition to buffer that startup supply down to a low impedance for the
control chip, until the supply gets going, and the low impedance
maintenance supply takes over. An ESR meter is your friend here ...

I don't have that particular schematic, but in general terms such
capacitors
are usually quite small ( 1 - 47uF) such values are easy to get hold of in
multilayer ceramic chip capacitors - and the electrolyte will never dry
out.



But MLCCs then have their own problems, excess heat from PbF fixing, lead to
cracks and then metal migration into the cracks due to the tiny geometries
http://web.archive.org/web/200805120.../news/rfa_feat
ure_07b.asp
I don't know the relative frequency of each failure process though

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

On Fri, 24 May 2013 06:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent to the cited author.]


I am repairing an LCD monitor that has the very common turn on problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?
Google 'marking code DFRG' and see if anything makes sense. Also, SMT
is a very generic term. If we knew the specific package, it would
help us help you.

Another resource, especially whre power supplies for LCD monitors are
concerned is www,badcaps.net/forum. Pictures help.

PlainBill

Here is a link to a picture of the transistor in question.

https://docs.google.com/file/d/0BxTb...EMTlDaW8/edit?
usp=sharing

(Note link above may be split by a line break).

The transistor package body is 2.5mm x 4mm. Lead spacing is 1.5mm.
According to a document I checked here at the next link this package is
a SOT-89 (also apparently referred to as a T0-243 or an SC-62).

http://www.nxp.com/documents/outline.../sot089_po.pdf

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

"Reinhard Zwirner" wrote in message
...
Ian Field schrieb:

"Arfa Daily" wrote in message

[...]
And the cap in the C6 position on Reinhard's schematic ...

I don't have that particular schematic, ...

Hmm, can't you see my posting as of May 24 with the link to that
schematic?

Wondering

Reinhard


The only link I can see on that post is carousel-design.

Maybe you could repost?

"N_Cook" wrote in message
...
Ian Field wrote in message
...


"Arfa Daily" wrote in message
...


"Ian Field" wrote in message
...


"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was
sent
to the cited author.]

In article , says...



Is there a "bleed-through" route for start-up?

I do not really know what you are asking about here.

Its common practice for the SMPSU control chip Vcc to come from an
extra
winding on the chopper transformer. Before the PSU starts up - there
has
to be some source of Vcc to get it kick started.

Very often there's a high resistance resistor (or 2 in series) from
the
+ve of the mains bridge to provide the initial start up supply for the
control chip - these resistors are very prone to going high/OC.


+1

And the cap in the C6 position on Reinhard's schematic is the one
component that I change more of on every design of switcher that I work
on, than any other component for no or intermittent start up. As the
startup resistor is such a high value, that cap has to be in
near-perfect
condition to buffer that startup supply down to a low impedance for the
control chip, until the supply gets going, and the low impedance
maintenance supply takes over. An ESR meter is your friend here ...

I don't have that particular schematic, but in general terms such
capacitors
are usually quite small ( 1 - 47uF) such values are easy to get hold of
in
multilayer ceramic chip capacitors - and the electrolyte will never dry
out.



But MLCCs then have their own problems, excess heat from PbF fixing, lead
to
cracks and then metal migration into the cracks due to the tiny geometries

Plenty of manufacturers make leaded & resin dipped versions - I've seen
values offered as high as 180uF.

So far I've always had sufficient parts from salvage, most often I add one
to the print side to take the edge off the ripple current after replacing
the electrolytic.

Frequently the error voltage sampling cap in a PSU is so small that a MLCC
is ready to hand with the exact value so the electro is replaced altogether.

"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

On Fri, 24 May 2013 06:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]


I am repairing an LCD monitor that has the very common turn on problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?
Google 'marking code DFRG' and see if anything makes sense. Also, SMT
is a very generic term. If we knew the specific package, it would
help us help you.

Another resource, especially whre power supplies for LCD monitors are
concerned is www,badcaps.net/forum. Pictures help.

PlainBill

Here is a link to a picture of the transistor in question.

https://docs.google.com/file/d/0BxTb...EMTlDaW8/edit?
usp=sharing

(Note link above may be split by a line break).

The transistor package body is 2.5mm x 4mm. Lead spacing is 1.5mm.
According to a document I checked here at the next link this package is
a SOT-89 (also apparently referred to as a T0-243 or an SC-62).

http://www.nxp.com/documents/outline.../sot089_po.pdf

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com


I have seen much much worse than that. If it reads ok, I probably wouldn't
bother too much about it ...

Arfa

Ian Field schrieb:
"Reinhard Zwirner" wrote in message

[...]
Hmm, can't you see my posting as of May 24 with the link to that
schematic?

The only link I can see on that post is carousel-design.

?????

Maybe you could repost?

Here is it:

http://www.bilder-hochladen.net/files/big/12b4-a6-6c52.jpg

Still wondering

Reinhard

On Sun, 26 May 2013 04:25:52 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

On Fri, 24 May 2013 06:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent to the cited author.]


I am repairing an LCD monitor that has the very common turn on problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?
Google 'marking code DFRG' and see if anything makes sense. Also, SMT
is a very generic term. If we knew the specific package, it would
help us help you.

Another resource, especially whre power supplies for LCD monitors are
concerned is www,badcaps.net/forum. Pictures help.

PlainBill

Here is a link to a picture of the transistor in question.

https://docs.google.com/file/d/0BxTb...EMTlDaW8/edit?
usp=sharing

(Note link above may be split by a line break).

The transistor package body is 2.5mm x 4mm. Lead spacing is 1.5mm.
According to a document I checked here at the next link this package is
a SOT-89 (also apparently referred to as a T0-243 or an SC-62).

http://www.nxp.com/documents/outline.../sot089_po.pdf
Excellent pictures, thanks. I believe the actual marking code is DF;
the R indicates the gain and the G is a prouction lot or date code.

My favorite source for arcane marking info: http://www.s-manuals.com

Which leads to: http://www.s-manuals.com/smd/df

And the datasheet: (watych out for line breaks)
http://www.s-manuals.com/pdf/datashe...d1898_rohm.pdf
IF you are in the USA, they are available from Digi-Key
(ww.digikey.com) for $.53 each. (Choose USPS First Class Mail for
lowest shipping cost.)

As a general rule, I dissaprove of replacing parts because they 'look
bad'. A few minutes making measurements with a DVM can give a wealth
of information.

PlainBill

"Reinhard Zwirner" wrote in message
...
Ian Field schrieb:
"Reinhard Zwirner" wrote in message

[...]
Hmm, can't you see my posting as of May 24 with the link to that
schematic?

The only link I can see on that post is carousel-design.

?????

Maybe you could repost?

Here is it:

http://www.bilder-hochladen.net/files/big/12b4-a6-6c52.jpg

As advised; you should replace C6 - even if it isn't the culprit, it can
cause all manner of nasty things to happen.

I'd use a low ESR 105 deg-C part - and I'd put a MLCC on the print side to
take the edge off its ripple current - but that's just my own preference.

"Arfa Daily" wrote in message
...


"Michael Karas" wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

On Fri, 24 May 2013 06:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]


I am repairing an LCD monitor that has the very common turn on
problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one
transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?
Google 'marking code DFRG' and see if anything makes sense. Also, SMT
is a very generic term. If we knew the specific package, it would
help us help you.

Another resource, especially whre power supplies for LCD monitors are
concerned is www,badcaps.net/forum. Pictures help.

PlainBill

Here is a link to a picture of the transistor in question.

https://docs.google.com/file/d/0BxTb...EMTlDaW8/edit?
usp=sharing

(Note link above may be split by a line break).

The transistor package body is 2.5mm x 4mm. Lead spacing is 1.5mm.
According to a document I checked here at the next link this package is
a SOT-89 (also apparently referred to as a T0-243 or an SC-62).

http://www.nxp.com/documents/outline.../sot089_po.pdf

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com


I have seen much much worse than that. If it reads ok, I probably wouldn't
bother too much about it ...


A little old lady once called me out to a TCE B&W 'portable' (has a handle
on top and is capable of 12V operation) one of those that the PCBs form a
box around the back of the CRT. The little old lady said it had horizontal
bars rolling up the screen, so she thumped it - then it went off!

Of course the PSU PCB is along the top (upside down) the TO5 driver for the
series pass TO3 was hot enough to melt its solder - when she thumped the
set, the TO5 dropped in the bottom of the case.

I had to go and get a replacement reservoir electrolytic to fix the original
cause, but the transistor that melted its solder was perfectly fine and went
back in.

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

Excellent pictures, thanks. I believe the actual marking code is DF;
the R indicates the gain and the G is a prouction lot or date code.

My favorite source for arcane marking info: http://www.s-manuals.com

Which leads to: http://www.s-manuals.com/smd/df

And the datasheet: (watych out for line breaks)
http://www.s-manuals.com/pdf/datashe...C_2sd1768s%2C_
2sd1863%2C_2sd1898_rohm.pdf
IF you are in the USA, they are available from Digi-Key
(ww.digikey.com) for $.53 each. (Choose USPS First Class Mail for
lowest shipping cost.)

As a general rule, I dissaprove of replacing parts because they 'look
bad'. A few minutes making measurements with a DVM can give a wealth
of information.

PlainBill

THanks for the info. I had also done some research on some other sites
and find that there are multiple possibilities for this device marked
with a DF.

Sanyo NPN 2SD1623
Philips PNP BF621
Siemens PNP BNF21
Rohm NPN 2SD1898 **

** The part that you located.

I agree that this part should not be replaced if it is working. I had
done some preliminary checking with the meter and it did not seem to
respond with any forward biased junction readings and so I needed to get
information as to whether this was some type of FET or a blown BJT
transistor.

When I get a power cord setup to be able fire up the board I will do
some checking. I may also need to rig up a temoprary heatsink for a
large diode bridge that gets screwed to part of the case that had to be
removed to get at the board. Initial tests can probably avoid that if I
just put small loads on the output rails for testing,

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

Ian Field schrieb:
"Reinhard Zwirner" wrote:
Ian Field schrieb:
"Reinhard Zwirner" wrote:

Hmm, can't you see my posting as of May 24 with the link to that
schematic?

The only link I can see on that post is carousel-design.

?????

Maybe you could repost?

Here is it:

http://www.bilder-hochladen.net/files/big/12b4-a6-6c52.jpg

As advised; you should replace C6 ...

It is Michael Karas who should try to repair his power supply by
replacing the capacitor corresponding to C6 (or the resistor
corresponding to R1) - not me! _I_ just tried to explain N_Cook's
"bleed-through" route by a typical SMPS schematic as an example.

Regards

Reinhard

wrote in message
news
On Sun, 26 May 2013 04:25:52 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

On Fri, 24 May 2013 06:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]


I am repairing an LCD monitor that has the very common turn on
problems.
This is an I-INC IF281D unit with model number showing as HSD1040. I am
in the process of replacing all the capacitors on the PhiHong power
supply board (model PSM217-404-H-R) and have noticed that one
transistor
looks like it got excessively hot. I would like to replace that
transistor but have to first ID the part number. To this end I have two
questions...

Does anyone know where it may be possible to get a schematic for the
PSM217-404-H-R power supply board?

The overheated transistor is an SMT device with a code DFRG marked on
top. Any idea as to what that part number may be?
Google 'marking code DFRG' and see if anything makes sense. Also, SMT
is a very generic term. If we knew the specific package, it would
help us help you.

Another resource, especially whre power supplies for LCD monitors are
concerned is www,badcaps.net/forum. Pictures help.

PlainBill

Here is a link to a picture of the transistor in question.

https://docs.google.com/file/d/0BxTb...EMTlDaW8/edit?
usp=sharing

(Note link above may be split by a line break).

The transistor package body is 2.5mm x 4mm. Lead spacing is 1.5mm.
According to a document I checked here at the next link this package is
a SOT-89 (also apparently referred to as a T0-243 or an SC-62).

http://www.nxp.com/documents/outline.../sot089_po.pdf
Excellent pictures, thanks. I believe the actual marking code is DF;
the R indicates the gain and the G is a prouction lot or date code.

My favorite source for arcane marking info: http://www.s-manuals.com

Which leads to: http://www.s-manuals.com/smd/df

And the datasheet: (watych out for line breaks)
http://www.s-manuals.com/pdf/datashe...d1898_rohm.pdf
IF you are in the USA, they are available from Digi-Key
(ww.digikey.com) for $.53 each. (Choose USPS First Class Mail for
lowest shipping cost.)

As a general rule, I dissaprove of replacing parts because they 'look
bad'. A few minutes making measurements with a DVM can give a wealth
of information.

PlainBill



Based on years of experience at component level, +1 on that. Unless there is
a very good reason, I've never been an advocate of 'shotgunning' for the
hell of it ...

Arfa

When I get a power cord setup to be able fire up the board I will do
some checking. I may also need to rig up a temoprary heatsink for a
large diode bridge that gets screwed to part of the case that had to be
removed to get at the board. Initial tests can probably avoid that if I
just put small loads on the output rails for testing,

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com


If available, I would strongly recommend the use of a proper bench isolating
transformer when working on this. I'm sure that it is probably a case of
grandmothers and egg-sucking as you seem to be saying the right things, but
just in case ...

Switchers are of course extremely dangerous on a 'raw' line supply. I
usually have a variac connected as well. This can be either a help or a
hindrance depending on design, but I always initially make the assumption
that it is going to be a help, when I don't have a schematic. Although some
supplies have UVLO on the control IC, so won't start with a reduced input
voltage, it does at least allow you to carry out checks on - for instance -
the startup supply, in a safe manner, and without the risk of a Disney-esque
fireworks display, when your meter or 'scope probe slips, which it always
will sooner or later, depending on how urgent the job is, and how rare the
supply is to obtain a replacement for ... :-)

Good luck with it, and do let us know how you get on !

Arfa

Michael Karas wrote in message
...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

Excellent pictures, thanks. I believe the actual marking code is DF;
the R indicates the gain and the G is a prouction lot or date code.

My favorite source for arcane marking info: http://www.s-manuals.com

Which leads to: http://www.s-manuals.com/smd/df

And the datasheet: (watych out for line breaks)
http://www.s-manuals.com/pdf/datashe...C_2sd1768s%2C_
2sd1863%2C_2sd1898_rohm.pdf
IF you are in the USA, they are available from Digi-Key
(ww.digikey.com) for $.53 each. (Choose USPS First Class Mail for
lowest shipping cost.)

As a general rule, I dissaprove of replacing parts because they 'look
bad'. A few minutes making measurements with a DVM can give a wealth
of information.

PlainBill

THanks for the info. I had also done some research on some other sites
and find that there are multiple possibilities for this device marked
with a DF.

Sanyo NPN 2SD1623
Philips PNP BF621
Siemens PNP BNF21
Rohm NPN 2SD1898 **

** The part that you located.

I agree that this part should not be replaced if it is working. I had
done some preliminary checking with the meter and it did not seem to
respond with any forward biased junction readings and so I needed to get
information as to whether this was some type of FET or a blown BJT
transistor.

When I get a power cord setup to be able fire up the board I will do
some checking. I may also need to rig up a temoprary heatsink for a
large diode bridge that gets screwed to part of the case that had to be
removed to get at the board. Initial tests can probably avoid that if I
just put small loads on the output rails for testing,

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com



Probably just incidental and irrelevant to the main problem, as it can only
get stressed while the SMPS is operational. I've still not seen you state
the identity of the supervisor/controller IC/s ? or is it discrete
componentry?

On Sun, 26 May 2013 13:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

Excellent pictures, thanks. I believe the actual marking code is DF;
the R indicates the gain and the G is a prouction lot or date code.

My favorite source for arcane marking info: http://www.s-manuals.com

Which leads to: http://www.s-manuals.com/smd/df

And the datasheet: (watych out for line breaks)
http://www.s-manuals.com/pdf/datashe...C_2sd1768s%2C_
2sd1863%2C_2sd1898_rohm.pdf
IF you are in the USA, they are available from Digi-Key
(ww.digikey.com) for $.53 each. (Choose USPS First Class Mail for
lowest shipping cost.)

As a general rule, I dissaprove of replacing parts because they 'look
bad'. A few minutes making measurements with a DVM can give a wealth
of information.

PlainBill

THanks for the info. I had also done some research on some other sites
and find that there are multiple possibilities for this device marked
with a DF.

Sanyo NPN 2SD1623
Philips PNP BF621
Siemens PNP BNF21
Rohm NPN 2SD1898 **

** The part that you located.

Note that the marking codes seem to be chosen by the manufacturer.
Always make sure you are dealing with the same package type.

PlainBill

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...


If available, I would strongly recommend the use of a proper bench isolating
transformer when working on this. I'm sure that it is probably a case of
grandmothers and egg-sucking as you seem to be saying the right things, but
just in case ...

Switchers are of course extremely dangerous on a 'raw' line supply. I
usually have a variac connected as well. This can be either a help or a
hindrance depending on design, but I always initially make the assumption
that it is going to be a help, when I don't have a schematic. Although some
supplies have UVLO on the control IC, so won't start with a reduced input
voltage, it does at least allow you to carry out checks on - for instance -
the startup supply, in a safe manner, and without the risk of a Disney-esque
fireworks display, when your meter or 'scope probe slips, which it always
will sooner or later, depending on how urgent the job is, and how rare the
supply is to obtain a replacement for ... :-)

Good luck with it, and do let us know how you get on !

Arfa

I will post back here when more work on this power supply has happened.
Normal workweek obligations force one to set aside tasks like repairing
monitors.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

In article ,
Michael Karas wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...


If available, I would strongly recommend the use of a proper bench
isolating
transformer when working on this. I'm sure that it is probably a case of
grandmothers and egg-sucking as you seem to be saying the right things, but
just in case ...

Switchers are of course extremely dangerous on a 'raw' line supply. I
usually have a variac connected as well. This can be either a help or a
hindrance depending on design, but I always initially make the assumption
that it is going to be a help, when I don't have a schematic. Although some
supplies have UVLO on the control IC, so won't start with a reduced input
voltage, it does at least allow you to carry out checks on - for instance -
the startup supply, in a safe manner, and without the risk of a
Disney-esque
fireworks display, when your meter or 'scope probe slips, which it always
will sooner or later, depending on how urgent the job is, and how rare the
supply is to obtain a replacement for ... :-)

Good luck with it, and do let us know how you get on !

Arfa

I will post back here when more work on this power supply has happened.
Normal workweek obligations force one to set aside tasks like repairing
monitors.

I see that even after all these years, you still haven't got your
priorities right 8^}

Isaac

On Tuesday, May 28, 2013 9:52:46 PM UTC-7, isw wrote:

... like repairing monitors.

I see that even after all these years, you still haven't got your

priorities right 8^}

Isaac

:^)

Priorities are just that . . . something that somehow gets set by what we choose to do.

Michael Karas

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

On Sun, 26 May 2013 13:08:53 -0700, Michael Karas
wrote:

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ,
says...

Excellent pictures, thanks. I believe the actual marking code is DF;
the R indicates the gain and the G is a prouction lot or date code.

My favorite source for arcane marking info: http://www.s-manuals.com

Which leads to: http://www.s-manuals.com/smd/df

And the datasheet: (watych out for line breaks)
http://www.s-manuals.com/pdf/datashe...C_2sd1768s%2C_
2sd1863%2C_2sd1898_rohm.pdf
IF you are in the USA, they are available from Digi-Key
(ww.digikey.com) for $.53 each. (Choose USPS First Class Mail for
lowest shipping cost.)

As a general rule, I dissaprove of replacing parts because they 'look
bad'. A few minutes making measurements with a DVM can give a wealth
of information.

PlainBill

THanks for the info. I had also done some research on some other sites
and find that there are multiple possibilities for this device marked
with a DF.

Sanyo NPN 2SD1623
Philips PNP BF621
Siemens PNP BNF21
Rohm NPN 2SD1898 **

** The part that you located.

Note that the marking codes seem to be chosen by the manufacturer.
Always make sure you are dealing with the same package type.

PlainBill

Well, I received the new capacitors for the monitor power supply and got
those installed. The power supply fired right up and produced its 5V
STBY output. I then tested the other outputs by connecting the PSON
signal on one of the connectors over to the 5V STBY and all of the +5, +
12 and +24 volt rails all came up. I tested the thing on the bench with
some load on each output and it works nicely.

Unfortunately when the PSU is mated up with the video controller board
in the monitor it fails to come up and act like a monitor. The only
thing that does appear to work is that the EDID device does provide
valid data back out through the D-Sub HD15 connector to a host computer.
It shows the proper native monitor ID strings and the correct native
resolution. But no other functioning is in operation.

Since this thing was given to me for free and the fact that it only
supports analog VGA signalling (no DVI connector) I will probably not
spend any more time futzing around with it.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

In article ,
Michael Karas wrote:

--snippage --

Since this thing was given to me for free and the fact that it only
supports analog VGA signalling (no DVI connector) I will probably not
spend any more time futzing around with it.

A while back, I acquired a very nice LCD monitor with both VGA and DVI-D
interfaces. At the time, the only interface adapter I had was VGA (this
is on a Mac which uses an external adapter). Later, I got a DVI-D
adapter and cable, and was able to compare the two. Despite my most
careful comparisons, using both text and images, I was unable to see any
difference in the image quality between the two.

VGA is not all that bad.

Isaac

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article ],
says...

VGA is not all that bad.

Isaac


I am inclined to agree that analog VGA can be pretty good. A lot depends
upon the quality of the cables, its lengths and how well the video
controller outputs are terminated.

Since LCD type panels will digitize the analog signal anyway there is
also a lot that can be done on a decent monitor regarding how the signal
is sampled.

In my personal experience with quite a variety of different LCD monitors
attached to an almost equally diverse array of different video driver
implementations I have both situations. In some instances where an
analog VGA to DVI direct comparison was done there was virtually no
discernable difference. On the other hand there were examples where
there was a distinct difference in the displayed image - even on a
monitor that had both DVI and analog VGA connections fed the same
content from the same video controller.
--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com