gjasmith

Yep, with the mod2 board there was no sound (despite the fact that the speaker wires come from the program card).

I finally managed to repair all the battery damaged tracks on the mod4 board though 

The sound worked but was noisy, getting worse when I move my hand near VR1 so I swapped it for the one from the mod2 which fixed it, it doesn't control the volume though, the program card controls that.

I also found someone who had posted a list of tracks he had to repair (although I can't find the post again to credit him) and using this as starting point made a small list of points worth checking which hopefully might help someone out.

 - Battery + side to R72
 - Battery - side to Ground (pcb underside)
 - Battery - side to C47

 - C47 top to T20 (E)

 - IC8 pins 10-18 to RU7 Pins 1-8 (payouts)

 - ZD26 to RU7 pin 1
 - ZD27 to RU7 pin 2
 - ZD28 to RU7 pin 3
 - ZD29 to RU7 pin 4
 - ZD30 to RU7 pin 5
 - ZD31 to RU7 pin 6
 - ZD32 to RU7 pin 7
 - ZD33 to RU7 pin 8

 - ZD34 to IC8 pin 19
 - ZD35 to IC3 pin 39
 - ZD36 to IC3 pin 19

 - IC23 pin 1 to IC7 pin 39
 - IC23 pin 2 to IC4 pin 39

 

Thanks, will concentrate my efforts on getting the MOD4 to boot then.