Hmm, crickets! Just to give some follow up. This unit has a processor card that plugs into a bus with two DIN 41612 96 pin connectors. One connector showed some corrosion, so this got me looking at it. Turns out that on pins 6 to 10 in all three rows, it was not making contact, plug through socket.
Sigh! So I took my time removing the connector. Another board where the designer used too small a hole size! But I cut all the pins one layer at a time, and I think I have got it out without too much damage. Now i need to wait for a connector to turn up, and I can see if I have fixed it, or if it needs more work. That work will be ugly. I did try to contact Waldorf, but no joy from them. And I beleive one of the Waldorf designers and gurus recently died.