fender pro tube twin amp

[whiskey outlaw]

i have a fender pro tube twin amp i beleive its known as the '94 amp - 3 chanel/reverb (no vibro). my problem is whan i plug in the footswitch (4 button type) the chanels sometimes have a life of their own sometimes swapping during mid song especially if i strum hard.

ive tried various leads(all mono 1/4" jack) into the pedal and amp but it has no difference.
ive read somewhere it is something to do with an optical device of some description on the circuit board.
has anyone got any advice?

[oldguy]

I've not familiar w/ these amphs at all, but I did try doing a search on them and it seems several owners had varying problems w/ them. So my advice would be take it to a tech who's familiar w/ them and have it fixed.