Motorola roundie

[Electronic M]

Back in the day TV techs used to find thermally dependent faults with freeze spray. Get some canned air or that old radio shack tuner cleaner that is basically oil that comes out of the can frozen and with the set on and the chassis jigged so you can access everything in the circuit with it running hit every component in the offending circuit a few at a time once warm and see which component when chilled puts it back to the cold operation state, once you find a region of the circuit that effects it narrow your chilling until you isolate the exact part that's causing it.