Zenith Chromacolor II loss of picture control after warmup

[RetroHacker]

I have a Chromacolor II, chassis 19JC48. The set works well, but after it's warmed up for a while, it will suddenly go to a very dim image, looking exactly like the picture control is turned all the way down. At this point, the picture control has no effect, but the brightness, color and tint still work. When this first happened, I hit it, and it popped back to working for a minute or two - I've not been able to repeat this, however. Turning it off and letting it sit for several minutes - it will work fine when powered back up. The problem seems random as to when it will happen - but it never happens when the set is cold and just turned on. Sometimes it'll happen after it's been on for an hour, sometimes two - this morning it only took about five minutes.

Obviously, this seems like a bad connection. I've been through this thing, I've traced the picture control back to the 9-88-03 luma module, and I can clip onto that and verify that yes, the resistance changes as the picture control is turned. The connections seem solid to the control and the stakes on the module connection, I have not been able to observe that going open. The resistor in series with the picture control seems fine and has not drifted. I've pulled the module and gone through it carefully, and resoldered a ton of what appeared to be bad connections - but the problem persists. I cannot make it go away when it crops up by wiggling or flexing modules, tapping or banging on anything. I went ahead and replaced all of the electrolytic capacitors on the 9-88-03 module - one of them was fairly bad, testing almost twice it's proper value - but again, this did not fix the problem. I'm beginning to wonder if there's something wrong with the ceramic resistor module (105-114-01), as that thing gets *hot*. I did try hitting the IC (221-96) with freeze spray when it fails, and could not change the problem. I'm kind of afraid to freeze that hot ceramic module though - that seems like it might break.

Unfortunately, I don't have the schematic for this set, this is one of those ones that Sam's doesn't have scanned in already. I've been working off schematics for a later Chromacolor II console that uses a lot of similar parts, but it has a 9-88-02 instead of the -03, and it doesn't have that weird ceramic resistor module either.

If anyone has any ideas (or the schematic for the 9-88-03 module), I'd appreciate it.

-Ian