repairing Boss BD-2 with issues

[luthierwnc]

Hi all,  I got an older Blues Driver to mod with an aftermarket product.  They shall remain nameless since they have no part in this fiasco.
I replaced the parts shotgun and it worked fine the first time.  A couple days later it failed -- signal passed when it was off but nothing when engaged.  I took it apart again and started testing for issues.  When it was plugged in as I checked on a scope for signal I heard a soft tssssst and smelled a  hint of burn smoke.    Hate that smell.  At any rate it is now dead.

I've since ordered another but want to make this a trial balloon for working on this type of circuit.  Every fix-it blog and vid I've seen are for people who have used the wrong polarity or wrong voltage.  My guess, and this is a guess, is that I dragged the PCB across the exposed edges of the aluminum box and shorted something inside.  I'll tape those next time. 
All of the diodes test fine.  I checked all the resistors.  Some are wildly out of spec but none were burned, dead shorts or open circuits.  I don't know how to test FETs but will spend a little time on the net finding more.  There is no sign of heat damage anywhere.  Some traces have fresh solder for new components but a close look saw no overlap.
Any other ideas on how to trace the gremlin?  Thanks for looking and wish me luck.  Cheers, Skip