This is a 41 inch rear projection TV from 1999. Acts as follows:

TV turns on normally, and produces a nice bright, sharp picture. Then, anywhere from 10 minutes to an hour later, the picture becomes monochrome and very blurry, with a striped interferance pattern of some sort. Same issue with both tuners, and all three video inputs.

Strange thing is, the on screen display still works normally, and is not affected by whatever is killing the picture. Tubes are in good shape, and don't really want to trash TV.

Would like to hear any ideas.

Found a schematic online. This TV is COMPLEX compared to the sort of things I usually work on. Studied the schematic long enough to have an idea what the different parts of the TV do, and ended up being able to reproduce the problem by moving a card back and forth slightly. Used some contact cleaner to clean where the card connects to the main board, re-seated it, and the TV appears to be working fine. If the problem re-appears, I'll pull the board the card plugs into, and re-solder. Maybe it's not old enough to be special to anyone, but after my brief experience working on it, I sure have a better appreciation for the effort that went into engineering this TV.