I'd previously put this down to a dry solder joint at the pot, but I've just traced round, and found that pin 1 goes to the bottom of C120, so I used a wire to bridge pins 2&3 to the top of C120, but no luck.
What else can I test?
Rimshot not working
Checked the pot to see if it had continuity to where it should, and sure enough found that the right side pin wasn't connected to anything - I must have damaged the trace when I desoldered it. I used a couple of short wires to connect it to Pin 2 of IC50 and C120 and it's now ticking away nicely 
So just the snare and the LCD to get working now, and then do the pin swaps on the transistors and the bass hum fix and I'm done.
So just the snare and the LCD to get working now, and then do the pin swaps on the transistors and the bass hum fix and I'm done.