[sdiy] Analog drum machine start/stop

[rsdio at audiobanshee.com]

On Jul 1, 2017, at 1:47 PM, Nicholas Keller <nirokeforums at gmail.com> wrote:
> While trying to trace down where the 22K resistor was on the PCB, I noticed that I installed the electrolytic connected to the volume pot backwards...I'm usually very careful about that sort of thing, so I'm not sure how that happened. But maybe that was the cause of the pop! I reversed that cap and changed the power source anyway as you suggested, and the pop is gone now. 

Looks like another vote against re-capping old synths unless absolutely necessary, otherwise equivalent to the old adage: Don't Fix It If It Ain't Broke.


> Now I have one or two more tasks before I can send this back.  I don't hear any snare at all, and the white noise adjustment trimmer (4.7K on this early model) only seems to pass signal when fully-CW.  Maybe the two issues are connected somehow, but I'm definitely hearing the cymbals so I'm getting signal from Q9 to Q14. 

Speaking of capacitors, I recently repaired a TR-808 which was missing its white noise for the Snappy and other signal uses. Turns out that there was a 10 uF capacitor in series with the noise source (for DC filtering) that had gone bad. Touching the cap brought back the volume to normal. Replacing that cap got things back to normal permanently.

Looking at the Rhythm-12 schematic that you provided, there's a 0.0047 uF cap in a similar position. No guarantee that it's the same problem, but you might try probing around the nearby components to see if something has failed.

Brian