Hello!

First of all, please forgive me my English, it is not my mother tongue...

I have a television set (Philips MD1.2E AA) of which the HOT was a short
ciruit. I replaced it and the fly-back capacitor as well. The man in the
store gave me a BU1508DX instead of a BU1506DX which was not in stock (but
which was in the TV); he said it was compatible. (Is there anyone who knows
whether this is true?) After inserting it, it immediately broke down again
and I took it out: it is as short-circuited now as the original one.
I can't measure a short-circuit in the primary circuit of the
HV-transformer. Is it likely that there is one on the secondary site? If
chances are high that after replacing it (and maybe some small other parts)
the TV will be okay again, I would not mind spending the money. Does anyone
have an idea about the price of such a transformer?
The power supply is making hick-up sounds.
Another peculiar thing: You know the sound a light-bulb makes when shaking
it? The same sound comes from the picture tube if one moves the TV gently
e.g. when putting the back side on again. It is also similar to the
"tsjinggggggg" sound my monitor makes after pressing the degauss-button
(without the first "click"). Is there a chance that there is a short-circuit
in the tube so that it demands too much energy from the transformer and thus
from the HOT?

I hope someone can give me some tips, thank You very much in advance!

Yours sincerely,
Rene

Possible LOPT breaking down,or lack of drive signal to the H-Output.
"Rene" wrote in message
...
Hello!

First of all, please forgive me my English, it is not my mother tongue...

I have a television set (Philips MD1.2E AA) of which the HOT was a short
ciruit. I replaced it and the fly-back capacitor as well. The man in the
store gave me a BU1508DX instead of a BU1506DX which was not in stock (but
which was in the TV); he said it was compatible. (Is there anyone who
knows whether this is true?) After inserting it, it immediately broke down
again and I took it out: it is as short-circuited now as the original one.
I can't measure a short-circuit in the primary circuit of the
HV-transformer. Is it likely that there is one on the secondary site? If
chances are high that after replacing it (and maybe some small other
parts) the TV will be okay again, I would not mind spending the money.
Does anyone have an idea about the price of such a transformer?
The power supply is making hick-up sounds.
Another peculiar thing: You know the sound a light-bulb makes when shaking
it? The same sound comes from the picture tube if one moves the TV gently
e.g. when putting the back side on again. It is also similar to the
"tsjinggggggg" sound my monitor makes after pressing the degauss-button
(without the first "click"). Is there a chance that there is a
short-circuit in the tube so that it demands too much energy from the
transformer and thus from the HOT?

I hope someone can give me some tips, thank You very much in advance!

Yours sincerely,
Rene

"Rene" ha scritto nel messaggio
...

store gave me a BU1508DX instead of a BU1506DX which was not in stock (but
SPPPPPPRRRRRRRRRRRRRRRR!!!!T
There's something that isn't ugual on those two xistors... they aren't
interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of 5.0V
and there are some diverse parameters...

I.

"Art" schreef in bericht
...
Possible LOPT breaking down,or lack of drive signal to the H-Output.

Dear Art,

Thank You very much for Your reply! There is a signal on the little
transformer that gives the signal to the base of the HOT, so I think that
won't be the problem. I ordered a new LOPT, I will post the results later.

Sincerely,
Rene

"Inty" schreef in bericht
...

"Rene" ha scritto nel messaggio
...

store gave me a BU1508DX instead of a BU1506DX which was not in stock
(but
SPPPPPPRRRRRRRRRRRRRRRR!!!!T
There's something that isn't ugual on those two xistors... they aren't
interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of
5.0V
and there are some diverse parameters...

Dear Inky,

Very funny, in another store they also said that their computer proposed the
1508 as a 1:1 replacement. I do not trust their computers. Well, I mean, I
do not trust the people who put this info into their computers.
I ordered a new LOPT and also two 1506's. When I have results, I will post
them here.

Thank You very much for replying!

Sincerely,
Rene

On Sun, 3 Jul 2005 14:35:45 +0200, "Rene" wrote:

"Art" schreef in bericht
...
Possible LOPT breaking down,or lack of drive signal to the H-Output.

Dear Art,

Thank You very much for Your reply! There is a signal on the little
transformer that gives the signal to the base of the HOT, so I think that
won't be the problem. I ordered a new LOPT, I will post the results later.

That signal on the base of the HOT has to be pretty-much perfect, or
the HOT dies.

Tom


Sincerely,
Rene

Rene wrote:
"Inty" schreef in bericht
There's something that isn't ugual on those two xistors... they aren't
interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of
5.0V
and there are some diverse parameters...
Very funny, in another store they also said that their computer proposed the
1508 as a 1:1 replacement. I do not trust their computers. Well, I mean, I
do not trust the people who put this info into their computers.
I ordered a new LOPT and also two 1506's. When I have results, I will post
them here.

A low saturation voltage is actually better. I think of the BU1506DX as
a cheap alternative, and seem to remember having replaced those with
BU1508DX's in the past.

---
Met vriendelijke groet,

Maarten Bakker.

"Rene" schreef in bericht
...
"Inty" schreef in bericht
...

"Rene" ha scritto nel messaggio
...

store gave me a BU1508DX instead of a BU1506DX which was not in stock
(but
SPPPPPPRRRRRRRRRRRRRRRR!!!!T
There's something that isn't ugual on those two xistors... they aren't
interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of
5.0V
and there are some diverse parameters...

Dear Inky,

Very funny, in another store they also said that their computer proposed
the 1508 as a 1:1 replacement. I do not trust their computers. Well, I
mean, I do not trust the people who put this info into their computers.
I ordered a new LOPT and also two 1506's. When I have results, I will post
them here.

Thank You very much for replying!

Sincerely,
Rene



Comparing the datasheets of both types reveals they virtually be the same
although the 1508s specs are slightly better. The VCESAT Inky mentioned is a
maximum so worst case. The actual VCESAT may be below 1V for both types.

The LOPT is a pretty expensive device. You can find many tips for checking
the it at:
http://repairfaq.ece.drexel.edu/sam/flytest.htm
a relatively easy to build tool at:
http://members.ozemail.com.au/~bobpar/fbt.htm

Although the LOPT might be defective, the control signal of the HOT is at
least as suspective. You hardly can check this out without an oscilloscope.
You need to check the frequency and the pulsewidth. The pulsehight may give
you an idea whether or not the pulse has enough power to drive the HOT
correctly. A positive DC level (p. e. caused by a leaky driver transformer)
will be disastrous for the HOT. For maximum certainty you'll need the specs
of the manufacturer.

petrus bitbyter

"petrus bitbyter" ha scritto nel
messaggio . nl...

Comparing the datasheets of both types reveals they virtually be the same
although the 1508s specs are slightly better. The VCESAT Inky mentioned is
a
maximum so worst case. The actual VCESAT may be below 1V for both types.

Ahem, my name's Inty, not Inky :-) They aren't 1:1 xistors !

I.

On Sun, 03 Jul 2005 19:26:06 GMT, "Inty"
wrote:


"petrus bitbyter" ha scritto nel
messaggio . nl...

Comparing the datasheets of both types reveals they virtually be the same
although the 1508s specs are slightly better. The VCESAT Inky mentioned is
a
maximum so worst case. The actual VCESAT may be below 1V for both types.

Ahem, my name's Inty, not Inky :-) They aren't 1:1 xistors !

I.


A perfect match for a HOT is hardly the most important aspect of its
survival, especially short-term. Slight disruptions in the drive
signal can be disastrous.

Tom

Tom MacIntyre wrote:
A perfect match for a HOT is hardly the most important aspect of its
survival, especially short-term. Slight disruptions in the drive
signal can be disastrous.

But after such defect has been fixed, a good match is necessary. Maximum
voltage ratings should be the same or higher, saturation voltage should
be the same or lower, switching speed needs to be the same or lower,
beta needs to be in the same ballpark. So don't go replacing a 2SD869
with a BU208 in most applications. It will run hot and blow.

---
Met vriendelijke groet,

Maarten Bakker.

wrote:
Tom MacIntyre wrote:
A perfect match for a HOT is hardly the most important aspect of its
survival, especially short-term. Slight disruptions in the drive
signal can be disastrous.
But after such defect has been fixed, a good match is necessary. Maximum
voltage ratings should be the same or higher, saturation voltage should
be the same or lower, switching speed needs to be the same or lower,

Switching speed needs to be HIGHER of course, the number of milliseconds
lower...

beta needs to be in the same ballpark. So don't go replacing a 2SD869
with a BU208 in most applications. It will run hot and blow.

---
Met vriendelijke groet,

Maarten Bakker.

"petrus bitbyter" schreef in
bericht . nl...

"Rene" schreef in bericht
...
"Inty" schreef in bericht
...

"Rene" ha scritto nel messaggio
...

store gave me a BU1508DX instead of a BU1506DX which was not in stock
(but
SPPPPPPRRRRRRRRRRRRRRRR!!!!T
There's something that isn't ugual on those two xistors... they aren't
interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of
5.0V
and there are some diverse parameters...

Dear Inky,

Very funny, in another store they also said that their computer proposed
the 1508 as a 1:1 replacement. I do not trust their computers. Well, I
mean, I do not trust the people who put this info into their computers.
I ordered a new LOPT and also two 1506's. When I have results, I will
post them here.

Thank You very much for replying!

Sincerely,
Rene



Comparing the datasheets of both types reveals they virtually be the same
although the 1508s specs are slightly better. The VCESAT Inky mentioned is
a maximum so worst case. The actual VCESAT may be below 1V for both types.

The LOPT is a pretty expensive device. You can find many tips for checking
the it at:
http://repairfaq.ece.drexel.edu/sam/flytest.htm
a relatively easy to build tool at:
http://members.ozemail.com.au/~bobpar/fbt.htm

Thanks for the links, I already ordered a new one at Lejos (30 euro's). Off
course they are useful for the future and the schematic of the tester is
great! (A pity You and Maarten did not reply to the post in the Dutch group,
I had been really hoping for that.)

Although the LOPT might be defective, the control signal of the HOT is at
least as suspective. You hardly can check this out without an
oscilloscope. You need to check the frequency and the pulsewidth. The
pulsehight may give you an idea whether or not the pulse has enough power
to drive the HOT correctly. A positive DC level (p. e. caused by a leaky
driver transformer) will be disastrous for the HOT. For maximum certainty
you'll need the specs of the manufacturer.

Hi,

I have the official service doc in which the shape of the signal on the
transformer that drivers the base of the HOT is displayed. I do have a
scope, I wrote that in the Dutch thread (sorry for multiposting instead of
crossposting, I normally never do that, but then, these groups have
different languages). The picture is not exactly the same. Unfortunately I
did not know where to get the mass for the scope, I chose to measure over
the transformer, as the side of it that is not connected to the base of the
HOT, is connected to "gnd 1". I hope the picture I get, is OK then (can't
think of a reason why not, but then, I am not an expert). The test point is
called "L2". Frequency and pulse-width are OK, the shape is not exactly the
same. I will have to check again for the DC-component as I was not aware of
it's importance when I was testing, I do understand it now. If the peak
level is not as high as on the doc (I remember it was lower because the
scope was to be put in 20 V/div mode while mine's maximum is only 10V/Div),
can it cause the HOT to die?

Thanks very much for replying.

Greetings,
Rene

On Sun, 3 Jul 2005 20:56:51 +0200, "petrus bitbyter"
wrote:


"Rene" schreef in bericht
...
"Inty" schreef in bericht
...

"Rene" ha scritto nel messaggio
...

store gave me a BU1508DX instead of a BU1506DX which was not in stock
(but
SPPPPPPRRRRRRRRRRRRRRRR!!!!T
There's something that isn't ugual on those two xistors... they aren't
interchangable, BU1508DX has VCESAT of 1.0V and BU1506DX has VCESAT of
5.0V
and there are some diverse parameters...

Dear Inky,

Very funny, in another store they also said that their computer proposed
the 1508 as a 1:1 replacement. I do not trust their computers. Well, I
mean, I do not trust the people who put this info into their computers.
I ordered a new LOPT and also two 1506's. When I have results, I will post
them here.

Thank You very much for replying!

Sincerely,
Rene



Comparing the datasheets of both types reveals they virtually be the same
although the 1508s specs are slightly better. The VCESAT Inky mentioned is a
maximum so worst case. The actual VCESAT may be below 1V for both types.

The LOPT is a pretty expensive device. You can find many tips for checking
the it at:
http://repairfaq.ece.drexel.edu/sam/flytest.htm
a relatively easy to build tool at:
http://members.ozemail.com.au/~bobpar/fbt.htm

Although the LOPT might be defective, the control signal of the HOT is at
least as suspective. You hardly can check this out without an oscilloscope.
You need to check the frequency and the pulsewidth. The pulsehight may give
you an idea whether or not the pulse has enough power to drive the HOT
correctly. A positive DC level (p. e. caused by a leaky driver transformer)
will be disastrous for the HOT. For maximum certainty you'll need the specs
of the manufacturer.

One particular Thomson chassis of the past comes to mind, the
TX-85/86. A 100 ohm, 35 VDC capacitor goes bad in the drive circuitry
(which used no drive transformer, by the way). The DC voltage starts
to float up from the desired -2.25 or so VDC, the negative spike's
peak rises to about -8 from -11, the HOT runs hot, and eventually
dies.

Tom


petrus bitbyter

Although the LOPT might be defective, the control signal of the HOT is at
least as suspective. You hardly can check this out without an
oscilloscope.
You need to check the frequency and the pulsewidth. The pulsehight may
give
you an idea whether or not the pulse has enough power to drive the HOT
correctly. A positive DC level (p. e. caused by a leaky driver
transformer)
will be disastrous for the HOT. For maximum certainty you'll need the
specs
of the manufacturer.

One particular Thomson chassis of the past comes to mind, the
TX-85/86. A 100 ohm, 35 VDC capacitor goes bad in the drive circuitry
(which used no drive transformer, by the way). The DC voltage starts
to float up from the desired -2.25 or so VDC, the negative spike's
peak rises to about -8 from -11, the HOT runs hot, and eventually
dies.

Dear Tom,

Thank You again. I have ordered several new capacitors to replace the ones
in the drive circuit. Perhaps I will replace some more (why not all of them
(well, not on the processor board maybe but I mean the ones on the large
signal board), they're not that expensive). I will also re-connect my scope
to the machine and see how much the shape of the wave differs from the one
in the service doc. And check whether there is a DC-component behind the
transformer.

Greetings,
Rene

Hi again!

Good news: The TV is Okay! I'm very happy about it and so are my parent, the
owners. It really was very educating, with my scope I studied a lot of the
signals in the line-circuit. A special message to Art and Tom: I had some
doubts about Your remarks about the importance of the shape of the signal
that drives the HOT (the doubts were caused by lack of knowledge on my
side): I must admit that You were very right. The line-drive transformer
turned out the "bad guy". On the base of the transistor that drives this
transformer, the signal was perfect, the shape of the signal on the
transformer wasn't steep enough by far.

Thank You all very much for helping me!

Sincere greetings,
Rene

On Mon, 11 Jul 2005 19:34:17 +0200, "Rene"
wrote:

Hi again!

Good news: The TV is Okay! I'm very happy about it and so are my parent, the
owners. It really was very educating, with my scope I studied a lot of the
signals in the line-circuit. A special message to Art and Tom: I had some
doubts about Your remarks about the importance of the shape of the signal
that drives the HOT (the doubts were caused by lack of knowledge on my
side): I must admit that You were very right. The line-drive transformer
turned out the "bad guy". On the base of the transistor that drives this
transformer, the signal was perfect, the shape of the signal on the
transformer wasn't steep enough by far.

Thank You all very much for helping me!

Sincere greetings,
Rene


Always nice to be involved in a successful venture...that's what this
group is all about. :-)

Tom