[sdiy] Analog drum machine start/stop

[Nicholas Keller]

Thanks to Ben and Brian for your help so far.  I got the snare working
after creating a board layout image and comparing that to the schematic.
Turned out to be a short between two pads pulling the snare to ground.

If you feel up to it, please check out the documents I
made/modified/compiled while working to trouble-shoot this machine.

http://Imgur.com/a/HBQcR

The schematic I posted previously has been notated to compare the
differences between this PCB and the late-model and to help navigate the
PCB layout I created.

 I'm curious about:

- the addition of C1 in the later version (no pads for this cap on this
version)

- the omission of D4 and the connection to Q9 (solder pads are present but
unused)

- the addition of the 10K resistor at the junction of C26 and D19 (no pads
for this resistor on this version)

- the drop in value of the White Noise Adjustment trimmer from 4.7K to 1K.
Currently, the white noise trimmer on this model does not produce a smooth
mix of noise level, but instead acts almost like a threshold where the
noise is heard only on the last few degrees of CW rotation.  Until that
point, the snare and cymbal blend is a quiet and slightly metallic ringing,
I assume this is the oscillator at Pin 11 of IC3.  Once the white noise
comes in, it completely overpowers the ringing, and the "snare" just sounds
like the cymbal with accent applied.  Does this indicate an issue at or
around Q6?  R and C values match the schematic.  Or, should I just replace
the 4.7-5K trimmer with a 1K?

Thanks for any insight you can provide, and hopefully this wonderfully
high-tech MSPaint layout can be of help to someone else in the future!

Nick
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