Doepfer

Hi Helitron, Florian,

> properly on there, and since it was working before it has to be some
> component that is dead. guess i have to exchange the potentiometers.

I'd be very surprised if changing any pots cures the problem, and 
besides, you could probably check that sustain pot is OK more easily 
by getting the envelope in a 'working' state (you seemed to suggest 
that was possible some of the time), and check the voltage at the pot 
wiper when in 'decay', so see if it varies much - should be something 
like close to 0V to around 8V maybe (looks like a 10k pot from 
Florian's photo).

I don't have that module, so I don't know the full details of the 
circuit and how it works, but from the photos Florian posted I'm 
guessing IC2 must constitute 'logic' which is controlling the 555, 
and that is where I suspect the fault will be. If the chips are 
socketted (?), a reasonable tactic would be to take the chips one at 
a time from the bad section (EG3), and try them in one of the good 
sections - if the good section continues to work, the chip is good, 
if not then you have id'd a bad chip. (If you put the chips from a 
good section into the bad the one, there is a small chance that the 
fault in the bad section might trash the good chip...)

I can't quite make out the IC2 designation on the layout photo, but 
it looks like it could be simply a quad op amp chip (TL084/064?), 
perhaps used as comparators, but that doesn't quite tie-in with 
the 'JPx' (?) boxes on the schemo, which control the re-triggering 
and the 'reset' pin of the 555. And reading the manual, on page 2, 
that the 'end of decay' switches at the sustain level setting, I 
suggest that what ever causes this is what is mucking things up!?

Tim