Crumar Performer -- Strange Behavior

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Riinehart
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Crumar Performer -- Strange Behavior

Post by Riinehart » Mon May 11, 2020 11:20 pm

Hi all,

Trying to diagnose some strange behavior with a Crumar Performer.

Short history: I bought it in a non-working state, but after replacing power supply caps, a heavy cleaning, and touching up any suspicious solder joints, everything worked fine for a brief, wonderful time.

Months later, I turned on to find all keys EXCEPT ALL B NOTES were almost silent, maybe 5% volume.

After some unsuccessful troubleshooting, I thought I'd try replacing the main voice chip, and bought a modern replacement 50240 from FlatKeys.

With the new chip in, I have a NEW set of odd behavior:

- All B notes are still good, although they sound a little glitchy
- All non-B notes have essentially the opposite sustain length from the fader setting. (If the sustain is set low, the B notes have a short sustain, and all other notes have a long sustain. Likewise, if the sustain is set high, the B notes have a long sustain, and all other notes have a short sustain.)
- A few notes are slightly glitchy sounding (consistent across octaves).
- One note (Bb) is very glitchy sounding, like garbled static (consistent across octaves).

So, to recap: some voice issues that follow the voice chip, but issues regardless of which chip is in, which makes me think it's somehow not the chip. But then why do the problems change depending on which chip is in?

Is there anything about the above that might set me on one path or another as far as what to look for and/or try next?

Many thanks for any help!

EDIT -- Manual here:
https://www.polynominal.com/site/studio ... manual.pdf

Riinehart
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Posts: 13
Joined: Mon Aug 28, 2017 10:05 pm

Re: Crumar Performer -- Strange Behavior

Post by Riinehart » Thu May 14, 2020 11:56 pm

Update: I've managed to narrow things down significantly, but desperate for some help.

Per the schematic, Pin 16 of the TDA1008s should connect to ground. After many hours of troubleshooting, I was able to find that Pin 16 of the chip that controls the B notes (the only notes that have been working) had continuity to ground -- but Pin 16 of all other chips did not.

Somehow there was a break getting from one side of the board to the other on the leg of a capacitor, which I replaced, and was happy to see that now I had continuity to ground on all Pin 16s. Yay.

Thinking I'd cracked the case, I plugged back in and ... no.

The GOOD thing is the sustain issue is now corrected. All notes sustain correctly according to the fader setting.

The BAD is that all notes now sound awful, the garbled white noise-ish sound that only a couple notes had previously.

Now I'm really lost. Here are some good things:

- the signal coming off the main voice chip is clean, loud, and steady for all 12 notes
- that same good, clean signal reaches Pin 15 of each TDA1008
- the voltage coming in to the TDA1008s matches the schematic ... +12v at Pin 1, +6v at Pin 13
- all outputs of each TDA1008 (Pins 2-6, each octave) are similarly bad sounding

And here's one strange thing, which I feel like is my only clue right now. With the power OFF, I have great continuity between all Pin 16s and ground. However, once I turn the power ON, there is increasing resistance between ground and each successive Pin 16, going from right (B note, about .7 ohms) to left (C note, about 35 ohms).

Is this normal? If not, I'm guessing whatever's wrong still has something to do with the ground connection. But I really don't know what to try next.

If anyone has any ideas, I would be so very grateful.

Thanks!

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