[sdiy] MG-1 issues

[john mahoney]

We feel for you, man! Everyone has run into mystery problems and we
know they are frustrating.

I don't recall if/how you've narrowed this down to the filter except
for the fact that you hear faint sound coming from the VCA when you
press a key. (Forgive me for not re-checking all the past posts on
this subject.)

Is there an audio signal at the filter's input? If so, the problem is
likely the filter. If not...

This may be the time to fall back to the standard diagnostic procedure
of tracing the signal path. Start at the beginning: Is the keyboard
producing a reasonable pitch CV? Cool. Is the VCO (or are there 2?)
receiving the pitch CV? Check. Is the oscillator producing sound? And
so on.

For tracing audio signals you can easily make an attenuating audio
probe from spare parts (free!). The ever-inspiring Ray Wilson has the
how-to on his Odds & Ends page:
http://www.musicfromouterspace.com/analogsynth/oddsandends.html#AMPSIGNALTRACER
You only need a voltmeter to trace CVs. A meter can also be used to
trace the audio, but it's cool to hear the signal at each step through
the synth.

Good luck!
--
john


----- Original Message ----- 
From: "Metrophage" <c0r3dump23 at yahoo.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, September 09, 2004 3:01 PM
Subject: Re: [sdiy] MG-1 issues


> Aha! I do have some 4007 ics, I had to pull them from the BBD clocks
I
> was making for everybody!
>
> Sure enough, replacing the 4007 did restore the envelope generator
> functionality! One annoying surprise problem solved!
>
> The output level is still minimal, and there is no low-pass
filtering
> going on. I have tried so many ways to try to understand. with my
> limited knowledge, what is going wrong here. I tested the 12v at the
> top of the ladder, the ground at bottom, and the voltages of the
rungs.
> I have replaced every IC on the control board, just to make certain.
> Replaced the 386 amplifier. All voltages and grounds appear fine.
> So...?
>
> I am beginning to experience very futile feelings, which make me
tired
> of working on this. How the hell could this thing have gotten so
messed
> up by sitting apart on a shelf in my garage for a few months? I am
so
> short of money I would definately not have bought the sliders,
> switches, etc if I knew that the synth wasn't going to work
properly! I
> have replaced pots on dozens of audio thingees without something
else
> getting mysteriously broken like this
>