The area on the underside of the board, beneath that huge heatsink and ancient IC, is fairly black and brown from the heat. It would be nice if I could upgrade that heatsink, as its obviously still getting VERY hot. Its right next to that ceramic resistor too, so that could possible be it. I'll post pics later of that, as well as some more in-depth pics of the components.
This board is very much like the Sprint 2 board, which I am fairly familiar with. If the area around that heatsink is getting excessively hot, the cause is most likely the 5 volt regulator in the middle of the heatsink. It is probably an lm323, which is an obsolete part, but I think cross references to an NTE931 (from memory, so double check). It also doesn't hurt to replace that resistor with one that is the same ohms value, but higher wattage so it can dissapate more heat.
Also, the volume is adjustable by a small pot by the large blue capacitor on the front left side of the board. On Sprint 2, there is a pot for each player, but not sure about yours.