LCD Monitor problem

[Al]

I picked up a used Micron AP150T at our town's recycling center. It cost
me nothing, so there is no loss if I can't figure out what's wrong.

When I hook it up to a computer, all works just fine. Then the picture
starts tearing horizontally after a few moments of on time. When I hit
the Function key, the function block pops up and looks perfectly fine
while the picture behind it is tearing.

So I assume that the sync signal from the computer is somehow being lost.
It does the same with two different computers, so the computer output is
not the problem; the computer outputs are fine with other monitors.

Any ideas? Is there a know problem with this unit syncing to the VGA
signal?

Al

 

[Wiebe Cazemier]

I picked up a used Micron AP150T at our town's recycling center. It cost
me nothing, so there is no loss if I can't figure out what's wrong.

When I hook it up to a computer, all works just fine. Then the picture
starts tearing horizontally after a few moments of on time. When I hit
the Function key, the function block pops up and looks perfectly fine
while the picture behind it is tearing.

So I assume that the sync signal from the computer is somehow being lost.
It does the same with two different computers, so the computer output is
not the problem; the computer outputs are fine with other monitors.

Any ideas? Is there a know problem with this unit syncing to the VGA
signal?

Al

Does it always happen after the same time period? Also when you don't allow
time to cool down? Perhaps it's simply a connection somewhere which gets
interrupted when the monitor warms up.

Do you have a scope? If so, you could track the input sync signals in the
circuit, and find out where it gets mixed up. If all VGA signal enters the ADC
correctly, then the fault will be a bit more difficult to find...

 

[James Sweet]

I picked up a used Micron AP150T at our town's recycling center. It cost
me nothing, so there is no loss if I can't figure out what's wrong.

When I hook it up to a computer, all works just fine. Then the picture
starts tearing horizontally after a few moments of on time. When I hit
the Function key, the function block pops up and looks perfectly fine
while the picture behind it is tearing.

So I assume that the sync signal from the computer is somehow being lost.
It does the same with two different computers, so the computer output is
not the problem; the computer outputs are fine with other monitors.

Any ideas? Is there a know problem with this unit syncing to the VGA
signal?

Al

Bad electrolytic capacitors are fairly common and can cause any number of
strange symptoms. That's where I'd look first, the surface mount sort used
in flat panels tend to be especially troublesome.

 

[Al]

Does it always happen after the same time period? Also when you don't
allow time to cool down? Perhaps it's simply a connection somewhere
which gets interrupted when the monitor warms up.

Do you have a scope? If so, you could track the input sync signals in
the circuit, and find out where it gets mixed up. If all VGA signal
enters the ADC correctly, then the fault will be a bit more difficult to
find...

OK, I'll do the check with the 'scope. And the time of the start of the
tearing does vary with the interval between startups; something must be
temperature sensitive.

Al

 

[Wiebe Cazemier]

OK, I'll do the check with the 'scope. And the time of the start of the
tearing does vary with the interval between startups; something must be
temperature sensitive.

That does not rule out capacitor based problems. I've repaired several
mainboards which had leaky capacitors, which worked fine as soon as they were
warm. It's the opposite to what you're experiencing, but it illustrates that
caps are temperature senstive.

 

[hr(bob) [email protected]]

That does not rule out capacitor based problems. I've repaired several
mainboards which had leaky capacitors, which worked fine as soon as they were
warm. It's the opposite to what you're experiencing, but it illustrates that
caps are temperature senstive.

If this is a crt monitor, there could be a high-voltage arc that is
not high enough to be seen or heard, but is generating "noise" that is
being picked up by some other circuit. A scope would be invaluable.

 

[James Sweet]

That does not rule out capacitor based problems. I've repaired several
mainboards which had leaky capacitors, which worked fine as soon as they
were
warm. It's the opposite to what you're experiencing, but it illustrates
that
caps are temperature senstive.

Capacitors are very temperature sensitive, more so than any other part I can
think of, aside from those meant to react to temperature.

 

[Wiebe Cazemier]

If this is a crt monitor, there could be a high-voltage arc that is
not high enough to be seen or heard, but is generating "noise" that is
being picked up by some other circuit. A scope would be invaluable.

Judging by the subject, I would say it is not a CRT

 

[Andy Cuffe]

Bad electrolytic capacitors are fairly common and can cause any number of
strange symptoms. That's where I'd look first, the surface mount sort used
in flat panels tend to be especially troublesome.

I second this. About 90% of the bad LCD monitors I see can be fixed
with new caps. Don't forget about the surface mount electrolytics on
the main board. I just fixed a Viewsonic that needed to have every
single cap on the main board replaced.
Andy Cuffe

[email protected]

 

[Al]

I second this. About 90% of the bad LCD monitors I see can be fixed
with new caps. Don't forget about the surface mount electrolytics on
the main board. I just fixed a Viewsonic that needed to have every
single cap on the main board replaced. Andy Cuffe

[email protected]

The display generated internally is just fine. Only the externally input
display tears. So it can't be "every single cap." I imagine it is
something in the sync input. I'll be checking it out. And like I said, it
is a "saved" monitor. If a quick fix won't do it, back to the dump.

Al

Al

 

[James Sweet]

The display generated internally is just fine. Only the externally input
display tears. So it can't be "every single cap." I imagine it is
something in the sync input. I'll be checking it out. And like I said, it
is a "saved" monitor. If a quick fix won't do it, back to the dump.

Al

Sure it could, may only be one or two that are bad enough to cause a
malfunction, but it's worth checking the rest. Usually when one of these
surface mount capacitors is bad, the rest are nearly shot too. I usually
replace them all, then the thing is good for years. In a pinch, one can
check the ESR of all of them and replace those that check bad. There's
usually only a dozen or so.

 

[Arfa Daily]

Sure it could, may only be one or two that are bad enough to cause a
malfunction, but it's worth checking the rest. Usually when one of these
surface mount capacitors is bad, the rest are nearly shot too. I usually
replace them all, then the thing is good for years. In a pinch, one can
check the ESR of all of them and replace those that check bad. There's
usually only a dozen or so.

Agreed, but be aware that the ESR values of surface mount electros tends to
be somewhat higher than those of a similar value in 'conventional' leaded
format, so a cap that you are expecting to read say 1 ohm, may correctly
read several ohms in surface mount.

Arfa

 

[Heinz Schmitz]

Usually when one of these
surface mount capacitors is bad, the rest are nearly shot too. I usually
replace them all, then the thing is good for years.

I'd be interested to know what makes you so sure that the caps
you bought for replacement are of superior longevity compared
to those the manufacturer did put in .

Regards,
H.

 

[Wiebe Cazemier]

I'd be interested to know what makes you so sure that the caps
you bought for replacement are of superior longevity compared
to those the manufacturer did put in .

Regards,
H.

Well, I guess by now that is over, but in the past, the market was flooded with
bad electrolytes. Some manufacturer copied a formula from another
manufacturer, but it contained a deliberate mistake to foul anyone who might
want to steal it. The result was that a lot of electronic equipment contained
these bad caps. Mainboard from around 2000 are very suspect for example. The
most likely cause form any mainboard from that period which has become
unstable, is the caps.

But the problem wasn't limited to computers. Even airplane electronics
contained them...

 

[Andy Cuffe]

The display generated internally is just fine. Only the externally input
display tears. So it can't be "every single cap." I imagine it is
something in the sync input. I'll be checking it out. And like I said, it
is a "saved" monitor. If a quick fix won't do it, back to the dump.

Al

Al

It's not unusual for bad caps to only affect the video from the
computer, leaving the OSD looking fine.
Andy Cuffe

[email protected]

 

[James Sweet]

I'd be interested to know what makes you so sure that the caps
you bought for replacement are of superior longevity compared
to those the manufacturer did put in .

Regards,
H.

Well for starters they don't have several years of use on them. All else
being equal, they're probably not. I hate surface mount lytics.

 

[Arfa Daily]

I replace them with regular through hole caps. It usually works without
any problems. Just bend over the leads and solder them to the lands on the
board. The biggest reason I do this is I can`t get smd stuff locally but
can get almost any value through hole cap.

Mike

That's interesting. On some Sony servo boards fitted to many of their CD
players a few years back, there were three sm electros along one edge of the
board, which used to go faulty, and occasionally leak. This gave the symptom
of either totally refusing to play, or very poor playability. If you tried
to sub regular electros for them, the board would never work again, even if
it worked, allbeit poorly, before. However, fit the correct sm types, and it
would immediately work again to full original spec.

Arfa

 

[James Sweet]

That's interesting. On some Sony servo boards fitted to many of their CD
players a few years back, there were three sm electros along one edge of the
board, which used to go faulty, and occasionally leak. This gave the symptom
of either totally refusing to play, or very poor playability. If you tried
to sub regular electros for them, the board would never work again, even if
it worked, allbeit poorly, before. However, fit the correct sm types, and it
would immediately work again to full original spec.

Arfa

Sony has a history of building things which are very particular about
the components used. I've had issues with some of the TVs not working
with subs that were fine in everything else.

 

[Arfa Daily]

Well I haven`t worked on nearly as much equipment as you have so, I`m sure
that there are plenty of things that you know that I dont. ;-) I am just a
novice and just mess around with stuff of mine that breaks or stuff I get
for free.

Mike

Well, if ever you get one of those Sony players - and there was lots of 'em
that used variations of the same board, mounted directly to the underside of
the deck - if it 'feels' like you've got a bad laser, look to see if it's
got those three caps along the edge of the board. If it has, you better
start looking for a supplier ... !! I never have figured out why 'standard'
electros won't work in that position. Like you, I have subbed leaded for
sm's in other places, without problem. About the only difference that I've
found is that the leaded types tend to have a lower ESR than the sm's, which
under normal circumstances, you'd say was a good thing.

Arfa

 

[Wiebe Cazemier]

Well, if ever you get one of those Sony players - and there was lots of 'em
that used variations of the same board, mounted directly to the underside of
the deck - if it 'feels' like you've got a bad laser, look to see if it's
got those three caps along the edge of the board. If it has, you better
start looking for a supplier ... !! I never have figured out why 'standard'
electros won't work in that position. Like you, I have subbed leaded for
sm's in other places, without problem. About the only difference that I've
found is that the leaded types tend to have a lower ESR than the sm's, which
under normal circumstances, you'd say was a good thing.

Arfa

Doesn't it have to do with higher stray inductance (more inductance, less
high-frequency shunt capability)? SMD parts are usually the only usable kind
of part in sensitive equipment, like PWM amplifiers.