OBERHEIM SYNTH

Have you tried the individual voice chip test so you can tell if one specific voice is drifting. I hear one out the six is off. The .0033uf capacitors on pins 4 and 8 of the CEM3396 voice chips control the frequency for each DCO input by timing the digital pulses from the 82C54 pulse generators. These timing caps can cause drift. By swapping the voice chips around you should be able to tell if the problem is another voice chip or the support circuitry. A scope may help to find the drift. Each timing cap should have a sawtooth waveform as the pulse goes from high to low. The frequency should be the same for all of these inputs as long as the same note is being played ex. A440. You're not using a noise patch so you can probably eliminate the noise inputs You could check and see if the noise inputs do this also.  
 
Good luck and let us know what you find. Probably somebody here in the group has been through these circuits with a scope. Personally I haven't but I can usually read the docs and understand what should be there.    


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> From: Andreas Östling <andreas85@...>
>To: oberheim@yahoogroups.com 
>Sent: Monday, August 12, 2013 5:48 AM
>Subject: [oberheim] Pitch Problems on Matrix1000 with working chips (audio attached) [1 Attachment]
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>[Attachment(s) from =?ISO-8859-1?Q?Andreas_=D6stling?= included below]  
>Hi, I've been trying to figure out the problems with my Matrix 1000. First of all I did the chip test and realized that three chips only had one voice, so I exchanged them for new ones. Now all chips are supposed to work. I have done the calibration tests and the two other "zeroing"-procedures in the test menu, but still get an annoying pitch problem (mp3 audio attached). I've recapped some of the unit, but it didn't help, the battery is changed as well (although I hardly think that could have anything to do with the pitch problem).
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>So in the attached mp3 I only trigger one note, but as you can see the pitch changes, after that I trigger an arppegio holding down _one_ note so you can see how the pitch "glides" from one place to another. Please help! :D I am yet to acctually play this resently bought synth ;(    
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