Env and decay not working, faulty mod.

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Mjolnaren
 
Posts: 1
Joined: Sat May 19, 2012 11:53 am

Env and decay not working, faulty mod.

Post by Mjolnaren »

Hello, Im having a bit of trouble with my TB-303.
I've been googling around a bit but I couldn't find anyone with the same problem.

About 2 years ago the evn and decay pot suddenly stopped working, the thing is that it has a kenton 5 socket mod,
but the idiot who installed it didn't ground the sockets.


The envelope is affecting the fitler but its stuck in the same depth regardless of VR5's position.

The decay does nothing except when accent is on. When accent is on it sounds like the decay pot affects the sound in the
same way the accent pot does.

I think that it would seem unlikley that both of the pots would fail at the same time.

A friend was kind enough to help me troubleshoot it and this is what we found.
(I don't remember exactly what it was but I think was something like this)

No signal from VR5 pin 3.

No signal or very weak signal from IC12 pin 5 or 4 or 3. (not sure)



The kenton mod adds CV-input sockets for:
Accent on/off
Slide on/off
Cutoff
CV
Gate

I got the schematics of the mod from kenton but I'm not allowed to post them. But I can say that it cuts off IC13's ground-trace and connects pin 10 of IC13 to C35.

I also suspect that the ungrounded CV-input for cutoff might have damaged Q9,Q10 or Q11.
How would I go about testing them? Do I need to desolder them to do that?


The only measuring equipment that I have is an analog multimeter and an analog oscilloscope. Maybe I need to get some better equipment to do the troubleshooting.

Anyone here got any idea of what might be the problem? Or what I should messure?
Any help is appreciated!

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