Hi Gordon, thanks for your reply, I'll certainly take a look into that. I've only just seen your reply actually - for some reason it wasn't picked up in the "show replies to your previous posts" section that I usually go to first when I log on here, so I just chanced upon it now.
When I opened up the Drumulator, there was some dodgy looking repairs and mods that had been carried out buy a previous owner which I have been slowly going through and returning to normal but still no go, but I have some suspicions....
I am wondering if the problem may be with IC 9B (LM 3086N a transistor array?) which had a diode added, bridging pin 7 and 8. There are signs of heat damage to the surface of the IC where the diode had been.
There was also a repair to pin 1 of IC 12A (CP8251) but as yet I cant find any info on that one. Hopefully the service manual will help. The pin had been pulled from the board and hard-wired to one leg of 3 nearby components, but with no obvious trace damage between those components and the IC, I don't know why this would have been done.
I'm waiting for the service manual to download now...