[sdiy] Sequential Conundrums -- The Final Chapter

[greg montalbano]

Finally resolved the problems on my two Sequential synths, and wanted to 
post this for the record.

First, the CEM3372 puzzle with the Prophet 600 (basically, there is one 
3372 VCF/VCA chip for each of the six voices;  I needed to replace two dead 
chips, but when I did, the new chips had radically different response to 
filter CVs than the old ones did, no matter which voice slot I inserted 
them into --
EVEN THOUGH the new chips performed perfectly in an external test circuit).
I tried adding a trim pot to add -5 volt offset to the filter CV, and that 
brought the new filters somewhat in line with the others.  Finally, I got 
some more 3372s from two other sources, and tried them out;  apparently, 
there are some 3372 chips that have DIFFERENT RESPONSE CHARACTERISTICS in a 
P-600 than the originals:  these have the manufacturing code ending in 
"A-01".  Chips with all other codes worked just fine.  I'm mentioning this 
because the CEM3372 is crucial to the total performance of the Prophet 
600;  it can throw off the tuning, shut out one or more oscillators, and 
generally play havoc with the VCAs.

Second, the ACIA chip in the Multi-Trak really CAN be partially functional 
-- MIDI IN worked fine, while MIDI OUT was totally scrambled.  Replaced the 
chip, and the synth is now perfect.  Also wanted to mention that a stock $4 
68B50 will work just a well as the $25 68A50 that Wine Country is selling.

Thanks to everyone on both lists who came through with support & suggestions.

~GMM