Digisound 80-7a

micromusic · Joined: May 05, 2014 Posts: 61 Location: england

Hi
Need some help with my latest module a Digisound 80-7a
I cant get this one to work so would any one like to help me by taking a photo of the pcb off a working module so I can compare with mine
I have used the one off http://www.digisound80.co.uk/digisound/modules/80-7.htm
and have found some errors but still cant get the damn thing to work and dont want to risk blowing the CEMS

Thanks

LFLab · Posted: Thu Mar 17, 2016 4:47 am Post subject:

Are the PSU voltages ok (when measured on the module)? Maybe pull the CEMs and check the voltages first.
With the module unplugged can you check whether there is a short from each rail to ground?

micromusic · Joined: May 05, 2014 Posts: 61 Location: england

Hi
Have all the correct voltages at each chip now but when I first powered up I was getting +29/-2.7 volts on areas of the board so I turned off quick and checked the pcb. Found a pcb fault and his has been has been corrected.

I can get sound through the circuit but sounds like its being overloaded by the signal in if that makes sense also the pitch of the VCO is being affected when the cut off pot is moved , I have checked and rechecked the pcb and wiring but as yet can find no other faults I have 2 more 3320s but am loath to fit them in case I blow them as I suspect the original 3320 fitted has died.

I will post some pictures soon

Thanks

micromusic · Joined: May 05, 2014 Posts: 61 Location: england

F*** F*** F***
Lost my 0v on my connectors strange how it happens just when I plug in a new module.
Any way tried again and still no luck can get a signal through it on some switch settings resonance seems to work but in a strange and reversed way[[/img]

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LFLab · Posted: Sun Mar 20, 2016 5:45 am Post subject:

That sucks, did you etch the board yourself? Did you check for shorts?
Troubleshooting sucks man, but in the end it usually is a "doh" moment.

micromusic · Joined: May 05, 2014 Posts: 61 Location: england

Hi
Yeah etched myself did check for shorts before I put the ics in all metered out ok
I have been playing with my scope and seem to get signals where I am supposed to just unable to get a good output

Think the CEMS may be dead!!

LFLab · Posted: Mon Mar 21, 2016 2:52 am Post subject:

Damn shame, and expensive too!

But with no IC's inserted, the voltages are all OK right? No short on the output pins of the IC's?
Should be OK to plonk in new IC's then.

Starspawn · Joined: Jun 14, 2013 Posts: 85 Location: Oslo

Ive got one of those, sadly not reachable without much trouble (stacked PCBs behind fastened large panels of even more stacked pcbs) but the digisound documentation was spot on for me, only the switch wiring was a bit hard to follow and I seem to remember using a common points instead of assigned ones for ground and maybe another.
The only odd behavior is the notch, but they do explain thats its an unusual approach. Attenuator before is bypassed when notched.

Maybe list what errors youve found in case its an misunderstanding?

AlanP · Posted: Mon Mar 28, 2016 9:08 pm Post subject:

Hate to say this, but you shouldn't've gone with a CEM design. By now, those probably need to be saved for repairs for polysynths that rely on them, plus if something goes wrong with the build, you have a module that relies on a fried chip.

It's a bit like trying to build a 960 sequencer with original RTL logic chips (provided you are not Moog Music!)

micromusic · Joined: May 05, 2014 Posts: 61 Location: england

I would love to save all my CEMS to rescue my large collection of Prophets, Memorymoogs and Oberheims or maybe some other fine polysynths like the Crumar Trilogy that one is really worth saving
If you have the odd Memorymoog sitting about with the CEMS blown I will happily take it off your hands
I used to deal with Paul Schreiber many years ago and he struggled to sell his stock of CEMS a very small niche market you see.
I like forums for the help people bring but it does irritate me when some comments are made.

micromusic · Joined: May 05, 2014 Posts: 61 Location: england

Made and tested a 80-6a today and checked all my 3320s, all work fine and the 80-6 lowpass filter is a rather nice sounding thing
So back to tracing whats wrong with the 80-7a