MOOG Micromoog troubleshooting

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MOOG Micromoog troubleshooting

Postby ultima » Mon Sep 17, 2007 8:10 pm

Im having problems with a Micromoog.

In short its low output and NO bass at all as well as the VCA creating a popping sound when set to fast attack.

But I have checked the synth thoroughly and all functions seem to work properly except for the mentioned problems.

Same Hipass result when running Pink noise into the audio input and the cutoff seems to start at around 600hz and severely cuts off at about 200hz resulting in NO low end whatsoever.
In fact when i turn down the cutoff the signal pretty much disappears.

I noticed in the service manual that the filter seems to be split into two sections.
Filter HI end ( 700hz to 1400 hz) and Filter Lo end (44hz to 176 hz ).
There could be a problem with the Filter Lo end section , it has a couple of LM 3046n Ic´s that i have tried replacing without any change.

So far i have tried changing a few caps as well as the output opamp but no luck.

Any ideas?
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Postby ultima » Thu Sep 20, 2007 6:13 pm

So , if you have problems with your Micromoog that manifests itself like this :
Severely Hipassed and Low Output and pops in the Loudness contour (fast attack)

Suspect the 601 IC /lm3080!

Thanks

Arnar
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Postby Maschinengeist » Sun Sep 23, 2007 10:56 pm

For the lack of bass (low end), have you checked transistors Q401, Q402 + capacitors C401 + IC304?

For the popping sound, it's usually the sign that the capacitors (especially in the power supply & associated section) are either dead or dying. Check the boards for dead and/or leaky electrolytic capacitors. They die after 10-25 years.

For the filter lo end, Q514, IC502, IC304 are to be checked.

Without goinf in details, I'd recommend that you have a serious look at the capacitors and transistors before heading to the ICs.

Hope that helps
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