Hi there - I know this post is old but it's always sad to see an unanswered question. You'll see several 4051 multiplexer ICs in a row. Those interface between the pots, the cpu, and the JX. Check the voltages (or do a diode check) on these. You may find that several of the pins are blown. It wouldn't be uncommon for these ICs to have reached their end at this age. Also take a look at and test the TL082 opamp and the LM311 comparator. You may find damge there too.
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Re: Roland PG-200 problem
2013-01-17 by Boddington