Doepfer

Hi Richard,
 
> It was fine a few weeks ago and I am pretty sure nothing like reversed 
> power could have happened - but what else could cause this? Seems like 
> the internal VCO is probably kaput?

The VCO output is jumpered to the MC1496 chips, so check that these are properly in place/making contact by sliding them off and on a few times - ST3 & ST4. Also, some of the chips may be socketted, including the PA382/CEM3382 chip which is the VCO - gently push them home to make sure that they have not worked loose.

Most of the trimmers on the board are for the phase-shifting filters; those that aren't are unlikely to stop the oscillator working even if they had been touched/moved.

The power supply requirements for the circuit are quite quirky too: two on board regulators provide +/-9V for some reason, and there is also a 'delayed 12V' rail (it comes up after than the main +12V rail I think), and which I think might be to ensure that the VCO does start-up when power is applied - this may be another reason for it not running, but I doubt there is anything simple to be done about it (if indeed that is the problem!).

If it isn't anything simple, it will probably take a scope to sort it...

Tim