Heat related problems are often easiest to find with freeze mist.
Pick up a can.
1) Spray a very small area at a time lightly. If no change let things warm up again. Then move on to another area.
2) If you find an area thats sensitive spray some on a Q-Tip & touch the individual parts with it. Wait a minute for results.
NOTE that chilling something to way below 0 F can cause oscillators
especially to go nuts. Tuners, hoz & vert. They straiten out when things
warm up again.
Beyond that I cant help. In the day we wouldnt touch these things with a
ten foot probe. We gave the customer the info on the MFG to send it
to them.
73 Zeno
LFOD !