MG-1 (or Rogue) Freq. drift

[brainmapper1]

Hi,
I'm reconditioning my Concertmate MG-1 and don't see this specific issue in the Service Manual - when I hold down a key, both tone sources stay in tune forever. But when set the "Tone Sources" mode to "Continuous" and press & release a key, Tone Source 2 slowly drifts down by about a semitone within 30-40 seconds or so (and continues). So I can wedge a matchbook in to use it functionally but I'd like to fix it if possible - or is this our cross to bear?

thanks in advance for any advice!
cheers
brainmapper1

(Rhodes Stage 73 / Hammond C3 / Yamaha DX7S / Moog MG-1)

[filtered]

30-40 seconds sounds like mine, back in the day- for a song-length drone, I'd use a piece of tape to hold her in tune- a matchbook wedged in might do more harm to the keyboard, in my opinion- but a MG-1/Rogue holding pitch indefinitely while "continuous"? the fix wouldn't be cheap, and you'd have to find the increasingly scarce vintage analog synth tech to work on it- so, yeah, get some tape, and bear that cross!

[Portamental]

Get it fixed and/or recapped by a tech.

Tone 1 and 2 on my MG-1 in continuous mode will stay in tune forever, with just the normal beating of oscillators together that is so characteristic of these machines. Once in a while, when you can get the detune slider of Tone 2 just right, there is almost no beating. I bet if high precision pots had been used by design, the beating would be even less, similar to my old school.

Before writing this post, I set up one of my MG-1's with minimal beating I could achieve (about 15 seconds). It's been like that for more than 30 minutes, both Osc still in tune, beating hasn't changed either.

MG-1 is a nice synth, worth putting a little money into. This particular one is modded with added VCF CV in and was owned by a tech from who I bought a year ago in top shape. I refurbished and recapped another one myself and it's pretty good too.

[brainmapper1]

Thanks for the responses you guys - and thanks for taking the time to test also.

I just communicated directly with another MG-1 owner I spied on Craigslist; he said he had "similar" problems, replaced 4 MM5823N frequency divider chips, and fixed it. I'm unsure how similar is similar at this point so I'll try to gather more details.

From my limited understanding, I'm guessing mine sounds more like a leaky cap (producing slow drift) than a bad chip (which I would expect to cause more dramatic consequences). I am ok with soldering/desoldering so I'd like to try it myself and reap the glory (or embarassment if I finally have to take it in later).

Thanks again - and I'm looking forward to more input.

cheers
brainmapper1

[varice]

Although undesirable, it is normal for the pitch to drift after the key is released. I modified my MG-1 to do the note “track-and-hold” better, but the pitch will still slowly drift.

A trick: I use a “D cell” 1.5V battery to hold a white key down. It is the right weight and shape, and it can be easily removed and/or moved to another white key. Works great for holding a long note for drones and such

BTW, the MM5823N chips have nothing to do with the release drift problem. Those chips are used in the poly section and have no effect on the oscillator Tone Source 1 or 2 pitch.