media at mail1.nai.net media at mail1.nai.net
Mon Jul 24 19:07:40 CEST 2000

I'm still trying to and an external clock input to the LFO of an SH-101 so
that I can sync the LFO and arpeggiator to the same external clock.  I'm
trying to install this mod from a diagram I downloaded from the web over a
year ago.  Unfortunately it isn't a very good diagram, it's quite vague,
and it's not a schematic.

Basically, from what I can tell, this mod takes the input of pins 2 & 3 of
IC3 (the inputs to an op-amp) and replaces them with the tip and sleeve of
the incoming clock using a double-pole switched jack.

However, breaking the connection between pin 3 and the preceding circuitry
kills the SH-101 -- the front panel lights display contradictory messages
and the unit makes no sound.  Grounding pin 3 seems to make no difference.
The Roland service notes do not show where pin 3 of IC3 goes -- the
schematics show it going to a dot with a line through it.  What does that

Tracing the connection from pin 3, it seems to go to pin 1 of IC1
(M5218L, which according to the service notes seems to be a dual op-amp in
a single-inline-package, no pin-out is shown).  Does anyone know the
pin-outs for an M5218L??  I'm guessing that pin 1 on the M5218L is Vcc and
connecting pin 3 of IC3 is a way of keeping at 5V.

This situation strikes me as odd -- that disconnecting the negative input
to an op-amp in a circuit that triggers an LFO would kill an entire synth.
>From what I can tell it causes a malfunction with the microprocessor.  The
reason why this strikes me as odd is that I wouldn't think the inputs to an
op-amp would draw that much current.  Any ideas??

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