Sony GDM500PS - Please HELP: red signal fluctuations

[krytron]

Well, I rushed here to post about my latest "progress report" of torturing the A board just to see your new reply and suggestion.
So I grabbed my magnifying glass, exposed the rear of the monitor to the direct sunlight and start looking for the bad soldering points. But I was not able to recognize the bad solder connections.

I've got the "picture" of bad solder from my experience with GDM1962B, but that is a drastic example. Perhaps I'm lacking experience, so I'll resolder everything in sight and reach.

However, I made a progress with "assistant", who were watching the picture while I was tapping the A board.
After a while, we found a hot-spot: it's the upper side/border just above IC402 and IC403. Those circuits are:

IC402: RGB drive
IC403: RGB OUT - outputs go directly to CRT (and it's very hot)

Tapping that part of the board induced the reddish-bluish-normal transitions.
But I was not able to induce the "blank frame" effect...

Now, back to the suggestion of recapping everything; there are several clusters of 10-15 electrolytes; they would cost me a small fortune! That is, if I don't want to install cheap junk that will dry-out in three months or so.
I have two nonworking PC motherboards with nichicon, sanyo, rubycon and elna capacitors.
Those are not junk caps, but they are not new.

One more issue I noticed while inspecting the board. The service manual shows this number as being printed on A board:
1-667-235-14 (171435014)
while my monitor has this number instead:
1-667-235-16 (171435016)
The only difference being 6 instead of 4 as a last digit. I wander why - perhaps because this unit have Sun logo and was shipped with a workstation?
Should check other boards (if possible) whether the number match or not.

Well, things are now converging - hopefully towards a final solution.

Thanks again for the suggestions and tips.


Best Regards.

[minnie]

Did you resolder IC402: RGB drive
IC403: RGB OUT?

[krytron]

Hello,

I had a few free days left and had to use them, so I was away from home for a while. Got home yesterday in the evening.

[krytron]

After resoldering the chips, I found that it is much harder to induce color changes by tapping the board than before. Unfortunately, spontaneous changes are even more frequent and more expressive than before.

I was wandering, is it possible that one of the chips (IC402 or IC403) is passing through "near-death experience", and it became sensitive to tapping? Meaning it may soon die.

From your vast experience, does it make any sense or not? Have anyone ever encountered similar problem and if yes, what was the solution?

Perhaps it is only some bad capacitor or solder point, but I'm slightly losing hope.
Please help...

Regards.

[krytron]

I have a new "conclusion" regarding my problem.

The color change is not actually reddish to bluish but rather reddish to cyan-like. This led me to the conclusion that the problem is only in the red signal level.

It's either above normal, which gives a red tone to the image or bellow normal, which gives a cyan tone to the image. Seems that only red signal is fluctuating, but I simply can't trace down my problem. If it's only the red signal, then it should reduce the "search space" for the problem. However, I'm stuck as I don't have enough experience with this kind of electronics.

It's quite remarkable and funny that hitting a D-board removed ghosting - reminds me on those movies where a good hit at the control panel (or whatever), at the right time, revives a plane, starship, etc. just in a last moment so the good guys escape from the bad ones.

My problem now breaks down to whether the fluctuating red signal is a consequence of a bad driver/amplifier chip, or something more trivial like bad capacitor or only a solder point(s).

But unfortunately, seems that I bored everyone in here to death with my problem.


Best Regards.

[krytron]

OK, no one seems to care about this thread, but I'll post my latest thoughts about the red-level issue.

The R/G/B signals reach the IC401 (PRE-AMP), then they go to IC402 (RGB DRIVE). The OSD, which is internally generated picture/signal, is also affected by red color fluctuations.
But the output of IC401 and OSD are "blended" in the IC402, which passes its output to IC403 (RGB OUT).
Therefore, the red color issue must be at or after IC402, i.e. either IC402 is faulty, or some component (like Cxyz/Qxyz/Dxyz) between IC402 and IC403 that carries R signal to IC403 is faulty (or fortunately just a bad solder), or finally there is a problem with IC403 or some of the Rxyz/Dxyz/Lxyz components carrying R signal to the tube (or again, only a bad solder).

Does any of it makes sense? Because if it does, then I'll try to resolder all red signal traces. The components are hard to get and are more expensive than the monitor is worth.

Thanks in advance.


Best Regards.

[krytron]

Now that all of you have put me on ignore, I can abuse my thread...

I created a full-screen test image: white stripe at the top with full screen width and 1/4 screen height plus three bars: red, green and blue adjacent to each other, 1/3 of screen width and 3/4 screen height.
Then I start staring... and observed that the problem is indeed only in the red signal.
But the confusing part is: red level is going above and below its normal value.
The question is can bad solder or capacitor cause the signal to go both above and below its nominal value?
Or is there a problem with a component (one of the two ICs mentioned in the previous post)?


Thanks in advance, just in case someone dares to type a word or two.