so i replaced the 4.7 ohm res. (had to find one) and that wasn't all of it.  the hum is there right when the amp powers up.  how would i be able to tell if the electrolytic capacitor was shorted- just replace it?  also i got the schematic from peavey.  it's too big to post.

hi i'm a first timer working on my peavey mark III.  i've used the amp (for guitar, though it is a bass amp) consistently for 3 years without a problem.  last week at practice i hit a chord and loud, awful hum came out.  the heat sink was red hot.  the hum persisted with or without a guitar plugged in until i shut the amp off.  today i tried it again and the amp functioned for about a half hour and then the same hum.  i opened her up and found one burned looking resistor.  if i'm reading right it's 4.7 ohms.  could this be all or part of the problem?     thanks.