Vintage Synth Repair

I suppose if mine were doing that, I would begin by seeing what kind of waveforms were coming out of  the source of those notes - the MK50240 Top Octave Generator chip. If all the notes look good coming out of the r e, I would follow one of the problem notes through the signal path until I get to the point where it is bad. If there are bad notes coming out of the Top Octave chip, besides a possible bad chip, it is possible something is shorting the output with another signal - another chip could have a shorted input (that ha ppen ed to me recently), there could be a tiny piece of metal that fell behind or between legs of a chip...


----- Original Message -----
From: "nchevatarevich@... [vintagesynthrepair]" <vintagesynthrepair@yahoogroups.com>
To: vintagesynthrepair@yahoogroups.com
Sent: Monday, September 15, 2014 3:10:37 PM
Subject: [vintagesynthrepair] ARP Quadra distortion on strings help (ARP Omni ciruitry)


 








'm getting a distorted and out of tune sound on the same four notes in two octaves. I have no idea where to start troubleshooting, so any suggestions are helpful. It is more prominent in the 4' range, although audible in the 8' as well. There are three other notes that are distorted only in one octave and only in the 4' range, although not nearly as noticeable.


ARP Quadra poly section is based on (and the same as, afaik except for keyboard triggering)  the ARP Omni. The Quadra has one more octave, altnough the schematic is the same, so I'm not clear on that. I So any tips on the Omni should apply here.








This is one of two faults I'm afraid....








Tjhanks