[sdiy] Help with troubleshooting MX-2000?

Nicholas Keller nirokeforums at gmail.com
Wed Jan 31 18:44:20 CET 2018

Is anyone familiar with the Multivox MX-2000 and/or Roland SH-2000?

My friend sent me one to look at and described it as having a "dying
filter".... however, I think the signal is getting lost before the filter
input.  I get signal coming from the VCO boards and at the output pins of
the two LM3216 on the WF board, but by the time it reaches the header which
connects the WF (waveform selector) board to the MT board, the "waveforms"
are flat or nearly-so at around -12V.  Maybe this is correct and my scope
is simply not accurate enough to show the expected oscillation.  Any ideas?

The MX service manual is a hand drawn near-copy of the SH service manual,
but it leaves out some information and they have the circuits divided onto
different circuit boards.   There are no PCB layout diagrams for the MX in
the service manual I found, and I can't view the component side of the WF
board under power so it's a bit tricky to prove around. As far as I can
tell, there is no short on the WF board pulling the signals down to near -V
(negative supply rail is -14V as it should be)


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