I am new to the forum and am looking for some help regarding repairing my favorite Randall RG50-112 combo amp. Over the years the distortion channel has intermittently stopped working and then would return to working, if I left it alone, for a few days. However, now it seems the problem has become more acute, and the distortion channel is no longer working. Both the normal channel and the distorted channel lights LEDs do not work when the amp is acting up like this. I opened up the amp to see if I could see any solder joints which may have been broken, and I found a cement (sand?) resistor that appeared to be disintegrating as there was powder below it on the PCB board. It is near where the distortion channel knob for master volume is located and thought that may be the problem. I am not an amp tech, but I can replace a component here and there if I know what to replace and how to diagnose it. However, I am a complete amateur/novice at electrical repairs. Any help would be greatly appreciated.