Guitar Amplifier Popping Noise

[dfox416]

Hi,
I have a 1987 Roland JC120 solid state guitar amplifier that I have been working on for a while but I have not been able to fix my problem. When the amp is on, it makes intermittent popping sounds. It seems to take a couple minutes before the popping sounds start and turning up the volume of the amplifier does not affect the volume of the popping. The first thing I tried was replacing the filter capacitors in the power supply section (this didn't work but it was probably a good thing to do anyways given the age of the amp). One time when I had the amplifier circuit out of the cabinet, I put a fan behind it and the popping noise stopped. I'm not sure how to interpret this. I have noticed that there is a small portion of the circuit that gets very hot when it is turned on (so hot that I cannot touch it for more than a second or two), but I don't know if this is normal or not. The hot part involves 2 transistors, a 2SB647-C and a 2SB667-C, as well as a few resistors, but again, I don't know if this is completely normal or not.
The schematic can be seen here: http://elektrotanya.com/PREVIEWS/45612216/23432455/hangszer/roland/roland_jc-120-82.pdf_1.png

Does anyone have any ideas what could be wrong with this amp? Any help would be greatly appreciated. Thank you!

[amyk]

Are the hot transistors Q7 and Q8? Those form a push-pull amplifier. I suggest checking the +15V supply to make sure that it is not too high, and the caps and resistors around there to see if any are shorts.

[PA0PBZ]

Does it stop when you plug something into the "MAIN IN"? If so, check the electrolytes between the volume control and the MAIN IN.
If it does not stop the problem must be to the right of the MAIN IN, check the electrolytes there (C16, C24...)