Minimoog D OSC 2 problems

Tips and techniques for Minimoog Analog Synthesizers
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normhart
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Joined: Mon Jan 26, 2015 11:25 am

Minimoog D OSC 2 problems

Post by normhart » Fri Jun 26, 2015 7:11 am

I switched on my Minimoog D today and noticed a problem with OSC 2. A very low frequency clicking sound - once every few seconds is all it sends out. Also, when moving the modulation wheel full up, I hear some faint output as well - at a higher more audible frequency. Is this a bad connection somewhere or just a dead component?

Update 7/2/15 Re-seated the OSC board and tried cleaning contacts - no luck. Looks pretty clean in there for a 30+ year old synth. Nothing looks burned out. I read a similar problem that was fixed with a replacement of the 741 component for OSC 2. Looks like I'm going to have to look for professional assistance here.

Thanks

normhart
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Joined: Mon Jan 26, 2015 11:25 am

Re: Minimoog D OSC 2 problems

Post by normhart » Wed Jul 08, 2015 11:32 am

07037F00-2CC9-4143-A6E2-D81F28EE51D3.jpeg
Here's a photo of the board
Last edited by normhart on Sun Dec 10, 2017 2:01 am, edited 3 times in total.

torinkrell
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Re: Minimoog D OSC 2 problems

Post by torinkrell » Tue Jul 21, 2015 12:26 pm

All three of the Minimoog Model D's oscillators can be switched to sub harmonic frequencies ("down into the clicks"). Perhaps the octave switch on your second oscillator needs attention/repair to bring its output back into the audio range.
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normhart
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Re: Minimoog D OSC 2 problems

Post by normhart » Sat Jul 25, 2015 2:56 am

Thanks for the info. The problem just happened 'overnight' as in one moment it was working perfectly and the next, what it's doing now.

normhart
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Re: Minimoog D OSC 2 problems

Post by normhart » Sat Nov 07, 2015 2:02 am

After reading of a similar problem from another owner, I thought I spend the 1.99 for a replacement 741 (ic4) and swap out the old one in the hope that this would work -which ended up not remedying the problem btw. Here is where it gets weird, though. After I replaced the board and started it up, I found that osc 3 was no longer working! Not long after, I was poking around checking the dc fuses just out of curiosity as to what they looked like and lo and behold, osc 3 decided to start working again! I am not by any stretch an electronics guy so, I would greatly appreciate any explanation of what exactly is happening here. Hopefully this would lead in some way to solving my osc 2 problem.

Thanks,
Norm

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thealien666
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Re: Minimoog D OSC 2 problems

Post by thealien666 » Sat Nov 07, 2015 1:16 pm

Almost always, that sort of spontaneous resolve is caused by bad or intermittent electrical contacts on the board connectors at the bottom.

Cleaning them invariably fixes issues.
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normhart
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Re: Minimoog D OSC 2 problems

Post by normhart » Sat Nov 07, 2015 8:23 pm

I've found this to be the case as well. Looks like it's time to do some cleaning.

Thanks,
Norm

normhart
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Re: Minimoog D OSC 2 problems

Post by normhart » Sun Nov 05, 2017 5:24 am

BC606B95-9251-4348-BAB8-93E4DC548406.jpeg
Well, after 2 years, 3 months and 25 days, I have a fully functional Minimoog again. It turned out to be a bad CA3046 ic. One side benefit is that in the process, I cleaned, checked and tightened up everything that needed it before finally getting to the real cause. There are a few loose ends that need attention, but it’s sure great to hear all 3 VCOs cranking away again :D

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