[sdiy] MS-20 stopped making sound...

[Andre Majorel]

On 2007-01-17 20:00 -0800, Arthur Giles II wrote:

> I picked up a Korg MS-20 a couple months ago and I have been
> loving it's fully working condition, until last night.  The
> MS-20 decided to only output the most minute of noises with
> volume fully turned up.  It's definitely the sound of the synth.
> I can hear the attack and release of the Envelope Generator and
> hear both oscillators but it is insanely quet.  I tried the
> headphone output only to get the same results.  I  hooked up
> another synth through the E.S.P. with it's sound routed to the
> external input and it also triggering the snyth.  Once again I
> could hear it only just way too quiet.  

Sounds like a problem with the internal VCA or EG2. I'd try the
following :

1. Re-seat the connectors inside.

2. With a voltmeter, check that the power supply delivers the
   intended voltages (-15 V and +15 V)

3. With a voltmeter, check that EG2 works. Set EG2 to (H, A, D, S, R)
   = (0, 0, 0, 5, 0). Press a key. The voltage on EG2 REV OUT,
   should drop to near 0 V. Release the key. The voltage on EG2
   REV OUT should climb up to 2.3 V give or take some.

Patching +5 V into INITIAL GAIN should turn the internal VCA on.

The service manual is available on korganalogue.net. It includes
the schematics.

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>
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