Sounds more like a "cold solder joint" on the amplifier circuit board. One or more of the soldered connections on the circuit board didn't get hot enough during the initial assembly, and are weak. A change in room temperature of less than 10ºF can cause the connection to be either made or not.
Your best bet would be to take it to a qualified electronics repair shop to have the board checked and the weak solder joints fixed. Under a high power magnifying glass, the weak joints will show up.