For my first post here, I have a stumper.  I just picked up a Princeton Chorus red knob amp.  Great cosmetic condition, the clean channel is great and the overdrive channel works, for a while.  After having the amp on for a few minutes and using input 1, the overdrive channel will just stop working.  You can push the amp switch or the footswitch, and the overdrive led lights up on the amp and footswitch, but the clean channel is actually working, the clean volume is working, and no overdrive.  If you turn the amp power off and back on, the overdrive is immediately back.  It does this with or without the footswitch connected.   I've cleaned pots and cleaned jacks.  I'm not a tech.... but I do own a soldering iron!  I'm just not sure where to start on this one.  I got the amp at guitar center, so my 40 days to return is running.  I love the amp for what it is, and I want to keep it. 

Anyone ever seen this before?  Any ideas?  Thank you all.