A visual inspection revealed nothing particularly noteworthy. I did notice that the two reverb pots had the back removed, pictured here:
|Fig. 1. The backs had been removed on both reverb pots. Note the board version|
on the left. You might need that when tracking down the correct schematic.
I removed the board from the chassis by removing the knobs, the plastic nuts on the input and footswitch jacks, and finally the nuts on the Preamp (Ch. B) control and the Ch. B Reverb controls using a 10mm socket (pictured below).
|Fig. 2. You'll need a 10mm socket for the nuts on the Preamp (Ch. B) control and the Ch. B Reverb pots|
|Fig. 3. I did not do this.|
|Fig. 4. The new jumper.|