[sdiy] MG-1 issues

[Grant Richter]

> Sound faintly plays through the filter, but there is no low-pass being
> done to it. I can tweak the cutoff pot and trimmer, but I never hear
> any difference. The resonance does work though, It oscillates at about
> 80%. I can hear any of the "mixer" sources: VCO1, VCO2, noise, ringmod,
> top-octave-ic. I would not be surprised if the reduced volume had
> something to do with the weird VCF behavior.
> 

Sounds like the filter is stuck closed.

Check to see if the voltage changes on the wiper terminal when the filter
control slider is moved.

Did you put the replacement filter control slider in upside down? Did you
forget to solder one of the pads? Did you solder bridge the wiper pad to
something else? Did you switch two sliders, or did the parts source supply
you with the wrong type or value? Was the repair part bad when you got it?
Was it late and you thought you'd finish something tomorrow, then forgot to?

Solid state is incredibly reliable. See if there is a mistake so simple, you
can't see it. Maybe someone in the supply chain made a mistake. Always
assume there is a mistake, or that your basic assumptions are wrong (like
the repair part was broken when it arrived).

Start over at the beginning and recheck every step. Look for the simplest
possible explanation for the problem.