fender princeton chorus problem

i have a fender princeton chorus amp that has serious electrical issues. sometimes it won't turn on when run through fully-working extension cords. if it's plugged into the same outlet as our PA amp, it causes a terrible hum in the system. and there's a vicious hum when my electro-harmonix memory man is plugged into it (the memory man works ok with every other amp i try). we've even had a shock or two just touching the metal screws on the casing.

i don't know jack about electronics. any clues?