Moog Music Forum

I recently bought a Realistic MG-1 at an estate sale and have been enjoying playing around with it. I removed the tar/foam and fixed a loose connection on an RCA jack. But I have one mysterious problem. The low F wasn't working. I removed the key to inspect and put it back in and it started to work. But, in some set ups, the low F plays only at a higher octave. It still a perfect F. Just an octave higher All the other keys work as they should in all settings. The F problem seems to be triggered when the polyphony slider is turned up.

I've looked at the service manual but don't see this problem discussed. Does anyone have any ideas? Thanks for any guidance you can offer.
David

There are two sound generators in the MG-1. One is basically a clone of the Moog Rogue, the other is a crude polyphonic organ type thing.

As the problem only occurs when the poly slider is turned up, it sounds like the polyphonic section is faulty.

The poly section of the MG-1 is a basic tone generator that uses frequency division to derive the notes. I'm guessing, but it seems likely that one of the divider chips has gone bad.

The divider chips are MM5832N which are pure unobtainium. They are the same ones used in the Polymoog. There are third-party offerings available (sometimes) but they are expensive.

Thank you very much. I will look for the replacement part.

Sorry, a follow up question. I see quite a few references to replacements for the MM5823N int eh MG-1. Is this the same as the MM5832, or a typo? Thanks in advance for your help.

5823 is the divider chip. There are three in the MG-1. I just replaced all three in my unit yesterday using the FlatKeys replacement chips and they seem to work wonderfully.

I replaced the chips with the FlatKeys items. And the problem of that note isn't fixed. The rest of the synth seems to work just fine, and frankly sounds a lot better than it did. But in organ mode (following the set up in the user's manual) that lowest note is still an octave off. Any further hints would be appreciated. Thanks.

The low F (F2) is handled differently than all the other notes in 'organ' mode on the MG-1.

The signal from the F2 key feeds into one half of U6 which is a CD4013 Dual D Flip-Flop. The other half of the flip-flop is unused.

This simply divides the frequency by 2 (or not, if it's busted!).

The obvious next step would be to replace U6 with a new CD4013B.

The CD4013B (and BE variant) are commonly available for pennies.

If that doesn't fix it, check the the solder joints and PCB traces around U6.

Well MoogNewbie seems to have disappeared. Damn! I really wanted to know how it turned out.