I've got a problem with an LCD. It powers on, but I can't get a
picture from it no matter which of the 4 inputs is plugged in. I
opened it up to look around, check connections etc.

As I was testing voltages at several points, I think I must have
shorted two points at some point, because I noticed that the monitor
had come on and I could see the built in on-screen display. So I know
that the monitor itself and the backlight work.

But I still can't figure out how to get it to actually detect input and
turn on.

Any thoughts on what the problem could be?

You will need the service manual, which I doubt you would be able to
obtain, and the proper set-up and spare parts to service your monitor.
If it is a very expensive monitor, you should send it back to the
manufacture's service people to have an estimate. You may find it more
feasible to replace the monitor.

--

Jerry G.


wrote in message
oups.com...
I've got a problem with an LCD. It powers on, but I can't get a
picture from it no matter which of the 4 inputs is plugged in. I
opened it up to look around, check connections etc.

As I was testing voltages at several points, I think I must have
shorted two points at some point, because I noticed that the monitor
had come on and I could see the built in on-screen display. So I know
that the monitor itself and the backlight work.

But I still can't figure out how to get it to actually detect input and
turn on.

Any thoughts on what the problem could be?

Well, I could get the service manual for about $25 online for this
model, so I may just do that.

I've managed to get it to turn on semi-consistently by briefly shorting
two pins on the Analog Devices AD9884A chip. When I short them there's
a high pitched buzzing that seems to be coming from the power supply,
then I release the short and the signal light goes green and I can
access the on-screen display. If I then do a Reset from the menu, it
correctly locates the input signal and shows it. However, I still
can't switch to other signals through the buttons, and if I try to use
the +/- buttons to switch display, I can no longer even get into the
on-screen menu.

Additionally, shorting those two pins doesn't work EVERY time, just
regularly.

I suppose it probably is best just to buy the service manual, though
I'm not sure it's going to offer any better suggestions.

Why not tell us what brand and model set you have? Without some specific
information it is hard to know if we can help.

Leonard

wrote in message
oups.com...
Well, I could get the service manual for about $25 online for this
model, so I may just do that.

I've managed to get it to turn on semi-consistently by briefly shorting
two pins on the Analog Devices AD9884A chip. When I short them there's
a high pitched buzzing that seems to be coming from the power supply,
then I release the short and the signal light goes green and I can
access the on-screen display. If I then do a Reset from the menu, it
correctly locates the input signal and shows it. However, I still
can't switch to other signals through the buttons, and if I try to use
the +/- buttons to switch display, I can no longer even get into the
on-screen menu.

Additionally, shorting those two pins doesn't work EVERY time, just
regularly.

I suppose it probably is best just to buy the service manual, though
I'm not sure it's going to offer any better suggestions.

I really wouldn't recommend shorting IC pins... you can easily destroy
them, if that hasn't already happened. The IC AD9884A is an analogue
to digital converter.

I've come across many odd faults with LCDs caused by low value and/or
bad ESR electrolytic capacitors. Visually inspect all of them on the
mainboard for bulging tops or leakage. Failing that, remove and test
them.

You can sometimes discover if an electrolytic capacitor is the trouble
by heating them with a hairdryer (don't roast them though!) and see if
the fault clears or alters in some way.

Otherwise you may be looking at a faulty IC somewhere.

Incidentally, has the OSD failed to come up since shorting the IC
pins? What are the numbers of the pins you shorted?

I use a hot-air station with small nozzle, whereas some just stick the
tip of their soldering iron on the metal top of the cap for a few
seconds, trouble with that is you can cook the cap quickly. One thing
you could do is get some thick card and cut a small circle in it for
the cap to go through, so it acts as a barrier to most of the heat.
If heating the caps does nothing, heating the whole board can tell
you if you have a bad joint somewhere... even surface-mount ICs can
suffer dry joints, often invisible to the eye.

Here is the ICs datasheet, it's PDF and if you scroll through it,
you'll find an image of it with all pins numbered:
http://www.datasheetcatalog.com/data.../AD9884A.shtml

You need a capacitance/ESR meter to test those slightly bulging caps
really. If you don't have one, substitution is the only way, and
probably a good idea if there is bulging present. Many bad caps don't
bulge or leak though, just so you can bear that in mind with the rest
of them.

Well, I replaced the two bulging caps with new ones, and unfortunately,
nothing seems to have changed. Still can't get a picture or on-screen
menu.

wrote in message
oups.com...
Well, I replaced the two bulging caps with new ones, and unfortunately,
nothing seems to have changed.


Something has indeed changed- you've eliminated two suspect parts and
prevented further trouble!

Dave

Okay... now I'm going to scream...

I started looking at the monitor again today after work, couldn't
figure out any more about it. Then about an hour later went back to
try a few more things... and it just worked when I turned it on.

I literally didn't do anything that should've changed anything about
it. This is after not working at work for a month or so. I just took
it when they gave up and were throwing it out.

I hate electronics

Well, I'm happy to say that now the monitor appears to be working
mostly correctly.

It won't come back from sleep mode, but turning it off and back on
brings it back.

Also there's a slight darkening of the picture at three corners, but
nothing that's going to bother me. (unless someone has an idea of what
that would be and it's an easy fix). I suspect it was more than likely
somehow caused by me during the inspection/repair process. Who knows.

Anyway, thanks for the tips/help.

It'll be very interesting to know which pins you've been shorting to
get it partly functioning...

Well, like I said, I believe it was pins 7/8 which is one of the color
inputs and a voltage pin I believe.

I'm not exactly rushing to try repeatedly

Understandable.

Measure the voltage on pin 8, should have 3.3V there.

Yeah, it's 3.3V at pin 8.

Assuming the chip was getting input though, shouldn't the R,G,B in pins
be at something (looks like between .5 and 1v from the spec). Because
none of those pins have a voltage, so I'm guessing the problem is in
getting the signal from the input to the chip.
Although that doesn't explain why I can't get the onscreen display
either.