[sdiy] MG-1 issues hopefully isolated

[Oren Leavitt]

Howdy CJ,

You might want to try and determine why the 4007 is hot before you plug in a new one.
It's possible that something else that's broken is causing excess current to flow through the 4007.

HTH,
Oren

-----Original Message-----
From: Metrophage <c0r3dump23 at yahoo.com>
Sent: Sep 8, 2004 11:13 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] MG-1 issues hopefully isolated

The advice to rest made my wife laugh, as she was reading over my
shoulder. Now I feel very much more lucid, but  don't ask me if I awoke
to the same level of genius as Harry!

I did some basic testing of supply and chip voltages, which are ok.
When I switch the synth on initially, there is NO sound, until I toggle
the "TONE SOURCES CONTOUR" switch... then I hear the LFO noodles, and
the keys work. Checking U14, the 4007, it is extremely hot! Edge wire
#20 drops in voltage when a key is pressed, but U14 pin 1 does not go
to 12v. Also, pin 6 stays at a steady 12v, which it is not supposed to.

I guess I should try replacing the 4007, which bites because I don't
have any, and am getting extremely devoid of money. A $20 order of
handy things to Unicorn is possible. Can one just replace the 4007 with
discrete FETs? My diagram of the 4007 doesn't say which pins are source
and drain, does it matter? I'll remove the 4007 and install a socket,
so I guess I can try. Then there's the question of whether or not this
is the only thing broken, I don't know, but I hope so.

CJ


		
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