MG-1 pitch drop

thiagozt · Post by **thiagozt** » Mon Jan 24, 2011 6:36 am

Hey, My ConcertMate MG-1 sounds great but I just noticed how the pitch drops after a couple seconds after I release whatever key was pressed. Does anybody have any idea on how to fix this? or at least where the problem could be?

Post by **cornutt** » Wed Jan 26, 2011 7:47 pm

The dreaded sample-and-hold droop... This is often caused by crud on the circuit board which forms a partially conductive path, allowing the sample and hold capacitor to discharge slowly. I'm not familiar with the insides of an MG-1, but I've read that there is some kind of foam that dissolves over time and gets all over everything inside. The first thing I'd try is pulling the boards out and giving them a good cleaning, if needed.

thiagozt · Post by **thiagozt** » Thu Jan 27, 2011 9:36 am

you're so right, that would make a lot of sense, the MG-1 is famous for it's disgusting foam-like material that surrounds sliders... I'll try that...

atkbg · Post by **atkbg** » Thu Jan 27, 2011 11:54 pm

Follow the advice above. However, the caps in that model weren't the best. Replacing that cap is pretty easy if you have soldering skills.

Horace · Post by **Horace** » Wed Dec 07, 2011 4:45 pm

You're in for a h**l of a foamy weekend

A flat razor-blade and isopropal does wonders though.
Schematic can be found here:
http://www.synthmania.com/mg-1.htm

emoji · Post by **emoji** » Thu Jan 02, 2014 10:22 pm

Sorry to necro an old thread but I am planning to start cleaning out the MG-1 this weekend. Would an ISOpropyl alcohol bath be safe for the board once I scrape all of the foam off? I plan on ordering a set of replacement pots/sliders/etc but would like to get it as clean as I can now without soldering or messing with anything. Thanks!

MG-1 pitch drop

MG-1 pitch drop

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Re: MG-1 pitch drop

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Re: MG-1 pitch drop

Re: MG-1 pitch drop