Moog "The Source" Repair help

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Svanis
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Joined: Fri Apr 12, 2013 2:54 pm

Moog "The Source" Repair help

Post by Svanis » Fri Apr 12, 2013 3:07 pm

My dad's an electrician and we're going to repair my Source this monday. The "Glide" function does not work whatsoever (The edit LED registers the button but nothing happens, adjusting the rate does not help.) and the pitch wheel goes up almost 12 semitones (to about 11½) and down 10 semitones. What are the default values, 12 and 12? Also, any ideas on what the problem with the glide could be and how to fix the pitch wheel etc would be appreciated. We'll go through the service manual that I printed out, but you guys could help to at least speed up this process. :)

The capacitors have been changed by the previous owner, I don't know if they're high quality or not yet, if not then maybe you guys have recommendations on ones that will yield the best sound?

Thanks in advance.

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thealien666
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Location: Quebec, Canada

Re: Moog "The Source" Repair help

Post by thealien666 » Sat Apr 13, 2013 12:20 pm

First, welcome to the forum.

Second, the Moog Source is a relatively complex synth, microprocessor driven, with many analog switches and multiplexers. There are a lot of things that can go wrong in this machine. And it can range from logic gates chips failing, to op amps failing, to membrane failure, to crazy behavior of the whole synth (famous voltage regulator contact pins oxydation), to... well you get the point.

For the pitch wheel range not covering 12 notes, its total range is not programmable and not specified in the documentation. It depends on the tolerances of components. But also on the accuracy of the +15 and -15 volts power supply (I would check that first).

As for the glide not working, it could simply be trimpot 19 (glide range adjust) not operating properly (oxidized) or possibly U17 (3080a OTA) that is defective (bias input not working)?

Good luck.
Moog Minimoog D (1975)
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Svanis
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Joined: Fri Apr 12, 2013 2:54 pm

Re: Moog "The Source" Repair help

Post by Svanis » Sun Dec 01, 2013 3:11 pm

Hi again! I'm resurrecting this thread after we finally got around to do this.

We had a look at the 3080a OTA. It was located under the keybed. It had been replaced before and was short-circuited. (the replaced chip wasn't even a 3080 ota) We put in a new 3080E OTA (all the 3080A were the round kind) and adjusted the trimpot a few times before returning it to its original position. There was no visible oxidation.

This didn't help, and the KB Glide is still not working. I can access it like normal as I always could through the membrane panel but adjusting the value does nothing, it goes from 0 to 99 with no difference, like it's fixed at 0.

Any help would be appreciated.

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thealien666
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Re: Moog "The Source" Repair help

Post by thealien666 » Mon Dec 02, 2013 8:22 pm

I would suggest replacing Q3 (2N3904) and Q4 (2N3906) next. Easily found, and inexpensive.
Moog Minimoog D (1975)
DSI OB6
DSI Prophet REV2
Oberheim Matrix-6
Ensoniq SQ-80
Korg DW8000
Behringer DeepMind 12
Alesis Ion

Svanis
Posts: 5
Joined: Fri Apr 12, 2013 2:54 pm

Re: Moog "The Source" Repair help

Post by Svanis » Tue Feb 18, 2014 4:24 am

Hello again, I did as you said and replaced them, I saw they had already been replaced before. It didn't solve the problem, unfortunately.

Is there anything else I could try?

electrojoe
Posts: 38
Joined: Sun Feb 04, 2007 10:15 pm

Re: Moog "The Source" Repair help

Post by electrojoe » Fri Mar 07, 2014 4:40 pm

Hello,
Sounds like you may have a "Control" issue.
I would look at the output of the de-multiplexor IC 4051 (U4 pin 15) with an "O" scope and see if you are getting a proper signal from the digital control circuits when adjusting the glide amount.
Also the buffer (U9A) may also be bad.

The next thing might be to seek out an experienced synth tech.

Hope that helps.

Gerry Dahl

Svanis
Posts: 5
Joined: Fri Apr 12, 2013 2:54 pm

Re: Moog "The Source" Repair help

Post by Svanis » Sun Mar 23, 2014 12:50 pm

Before you posted electrojoe, the culprit was identified. It was indeed U9a. It was replaced and everything is in working order. Thank you everyone! All that remains now is to get rid of the very slight crackle when adjusting the filter cutoff around certain frequencies. (Kind of like a bad volume pot, although very faint.) Even at low OSC levels (i.e when the filter is not overdriven) it appears. We'll look into it but any advice is still appreciated. :D

I have also cleaned the pitch bend wheel, and it doesn't crackle anymore. I also painstakingly tuned the oscillators. (Hard tune on the trimpots and soft tune by holding "Store" and "Osc 2".)

As thanks, I might record another demo now that the glide is functional, but you can still listen to my other impromptu demos here, before the repair:

https://soundcloud.com/svanis-1/moog-source-solo-testing

https://soundcloud.com/svanis-1/moog-source-s-h

https://soundcloud.com/svanis-1/manoir-de-mes-reves-moog

https://soundcloud.com/svanis-1/isnt-sh ... oog-source

https://soundcloud.com/svanis-1/blue-daniel-moog-test

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