Yet another Poysix repair

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sad_1024
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Yet another Poysix repair

Post by sad_1024 » Tue May 19, 2020 5:40 pm

Hi everyone

Long time lurker, first time poster. I am literally going insane on a Polysix repair. Thought I'd post here hoping to get advice by someone more experienced.

The synth has been fitted with a new KLM-367 repro board. I have salvaged the original 8045 MCU and a couple of other bits. The remaining are all brand new components.

I am having the exact same problems before the board change. Basically the filter cutoff, filter envelope amount, keyboard tracking and pw/pwm controls operate with a very slow response. As the pot is turned, the corresponding parameter slowly sweeps to the desired value.

Probing the outputs on the 4051 IC18 / IC19 while turning the knobs confirms that on the corresponding signals the voltage changes much slowly compared to the controls that are properly working.

I have tried disconnecting the other boards and just leaving the KLM-367 alone with the front panel boards and the same behaviour persists.
I have replaced the 4051 and the buffer opamps just out of desperation but obviously no luck.

I am pretty sure the problem must be on the KLM-367 and I am starting to really suspect perhaps the 8045 MCU might have been corrupted ? I don't know if that would be even possible, I am making a guess just because the other parts are new.

I have completely ran out of ideas and it would be great if someone can give any suggestions.

Thanks in advance

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Alex E
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Gear: Jupiter-6, Juno-60, Polysix, Emulator II, DX7, QX1, Arp Odyssey MKII, ESQ-1, Miami, M1r, Live 9, iMac MC309XX/A
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Re: Yet another Poysix repair

Post by Alex E » Fri May 22, 2020 4:34 am

I recently had my tech resurrect a Polysix from the same state. I put the new CPU board in myself but he fixed a lot of bad wiring and grounding issues.

It behaved almost the same way yours did before I started leaving it turned on all day, every day. Sometimes I had to sweep through the whole parameter to get it to "wake up" and become active. Now it picks up knob changes instantly like a normal synth should. It became a lot happier once it was allowed to warm up every afternoon for hours and hours.

Only bug I'm noticing now is the MG has a slight delay before it starts modulating anything. Doesn't have the same delayed effect with the mod wheel. Does yours do that too? I don't know if that's normal polysix behavior.

I wish I could help a bit more. I bought my CPU board used and pre-assembled. It's an older build and not the most perfect soldering work but it seems to get the job done.
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sad_1024
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Re: Yet another Poysix repair

Post by sad_1024 » Fri May 22, 2020 2:08 pm

Hi there

the synth shouldn't require warming up to react properly to knob changes. If that's the case I think there must be a problem somewhere perhaps some IC or transistor has become temperature sensitive.
In my situation the problem is present at all time even after the synth has been powered on for a long time.

Regarding your problem with the MG, with the delay control at 0 there shouldn't be any delay at all.
I would start by going through the calibration procedure for the MG section and see if you can obtain the correct levels and frequencies. There are two socketed LM13600 that needs to be selected for the correct operation of the MG.

I have ordered a new MCU, even if that's not the problem it will be useful to keep as a spare. I have also found another Polysix that needs repair and I'm gonna buy that as could be really helpful in narrowing down the problems... Or perhaps ending up with two synths that I cannot repair !!!!

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