More tinkering with sick LCD

[JM]

I've been playing with a broken LG 566 LM LCD screen I got my hands on. I
posted about it about a week ago, and I've since replaced all of the caps on
the main board with no change in the symptoms.
I started poking around on the board checking voltages as best I could by
following traces from the power input lines, and I noticed that there are a
few caps near the two ribbon connectors that run to the actual LCD panel
that have voltages written next to them in the silkscreen. The voltages
written are 9.2, 3.3, 18, and -6 volts. The caps themselves are rated well
above these values.

Measuring between the positive side of these caps and ground with the unit
powered on, I get nothing above 4.5 volts -- does that seem odd, or is there
something about the way I'm measuring that would give me false readings?
I do have good voltages at the input from the power supply, 2x5v and a
single 12v, but since the one visibly bad cap that I replaced in the power
supply was on the 12v line, I'm wondering if there is some component on the
12v line of the main board that shorted or went open and is causing
problems.

If anyone knew where I might be able to find a schematic for this unit that
might help me out, I'm by no means a professional tech but I like to learn
what I can by tinkering with broken gear... especially when there's nothing
to lose, as in this case! All I have is a DMM and some spare time once in a
while, but I'm hoping I might get lucky and find one bad part that is the
culprit.

Thanks in advance for any help!

 

[JM]

Just wanted to follow up on my post about the LG 566LM lcd screen I asked
about a few weeks ago. Long story short, it suddenly started working on me
one day after a few hour long visits to the freezer, but would gradually
degrade as it was left powered up.

I bought some freeze spray and was able to narrow the location of the
temperature sensitive part to one region of the board. By freezing the end
of a Q-tip and probing in that area, found a single SMD cap that, when
frozen, brought back a nice clean picture. The cap was between pin 5 on an
AIC1341 chip and ground, so I removed it and installed a regular old cap of
the same value directly between that pin and a nearby ground. Works great
now!

 

[Bart Bervoets]

Cool fault searching trick (excuse the pun).
Must remember that.

Bart Bervoets