Hi, maybe someone has an easy solution to this:
a friend of mine has a Sony KV C2521S that does as follows:
When using the AV composite input it first works fine.
After the set has warmed up, just unplugging and re-connecting the connected DVD player or switching the set off and on will kill the colour. All is B&W.
The internal tuner will still work in colour.
I don't have any schematics and haven't touched any CRT TVs for a long time. Could it be that simply tweaking an oscillator could fix the problem?