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sammichFM weird distortion behavior


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I got hold of one of those aluminum-case probably-bootleg sammichFM and have been playing with it for a couple weeks.  It wasn't in the best shape and I've fixed up a couple small issues already.

I noticed a weird behavior that I'm sure is totally obvious to someone smarter than me:  notes will crackle and be distorted a bit out one stereo channel, then out the other, in groups of three.  That is, if I play three notes in a row, they'll all be distorted on the left, then the next three I play will be distorted on the right.  Also, if I play a three-note chord over and over, that counts as the three notes, and the distortion will jump from channel to channel with each chord.

My suspicions contain thoughts about polyphony and voices per channel and so forth, but I'm already in over my head.  I imagine one of the OPL DACs and/or one of the op-amps is needing to be replaced but I have no idea how to track that down without just starting to desolder SMDs off of the board which ouch.

Anyone have any guidance about how next to debug this?  I've attached an MP3 of playing notes and chords;  the stereo distortion-swapping effect is probably best heard through headphones.


three note distortion.mp3

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