Korg Poly-61 fix

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Korg Poly-61 fix

Postby wez » Sun Jun 17, 2012 4:24 pm

It was almost 25 years ago to the day that I bought my first ever synth - a Korg Poly-61. I have a very close affinity with this guy, it changed my life.

Anyway, lately I've been on a bit of a nostalgia trip, buying up old synths that I had (or lusted after) as a teenager (i traded the Korg for a Yamaha RX-17 drum machine... yeah i know). so I've picked one up for next to nothing, with a couple of issues of course. It is the later revision (but pre-MIDI).

I've been over it and I suspect there's a problem with DCO1. All the voices are working, the EG is fine etc. But everything sounds like it is 2 or 3 octaves higher than it should be - i.e the bottom octave sounds ok, but as if it where the top octave. adjusting the DCO1 pitch (16' 8' 4' etc) doesn't change the octave, but it does effect the volume of the patch. When I set DCO2 to a different interval, I'm only hearing one note - suggesting DCO1 is silent. BUT when I set DCO2 to 'zero', i'm still hearing the tone. There's also a low level noise with each note, which is the same pitch across the keyboard. Bad IC perhaps?

I've also noticed that where the power supply connects to the chassis ground (under the flat ribbon cables between the CPU and Voice boards), there is a second ground cable that goes from there to nowhere - surely it should be hooked up, but I can't figure out where. I have looked and looked at pictures online but can't see where it goes, and the schems don't seem to show it.

Other than a few dodgy key contacts (standard for the Poly-61), it all works fine - all front panel controls are ok, all the programming parameters function correctly. The CPU board does have the remnants of a battery leak - it's not too bad, and the battery has been replaced - so i've pulled that board to clean it up a bit, one or two caps that appear to be effected, and a couple of the ICs have a bit of corrosion on the pins - i'll probably pull them, put some sockets in, and try swapping them around. Much of the bottom of the board has that light, 'fuzzy' corrosion, probably from battery vapours - should I wash this with MEK or would alcohol be enough?

I'm not brilliant at this sort of troubleshooting, but I'm keen to get better at it - so any advice or suggestions would be warmly welcomed!

w
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Re: Korg Poly-61 fix

Postby Futureman » Sun Jun 17, 2012 5:47 pm

I restored a P61 a few months ago.

Mine had lots of issues caused by corrosion.. Including some wacky pitch issues.

I'd check the traces for corrosion. Buzz them out. I had a few that looked ok but were open circuit. Putting jumpers across them fixed most of it's issues.

Cool synth. I slapped a midi kit in mine. They can move a surprising amount of air.
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Re: Korg Poly-61 fix

Postby wez » Mon Jun 18, 2012 6:55 pm

Hey thanks Mike.

Well I think I fixed the bastard. I took out the CPU board, replaced a dodgy looking cap, cleaned as much corrosion off as i could (i'll go over it again with some MEK when i get some, and deoxit as well).

But i suspect what fixed it was simply changing the battery... in the back of my mind i'd been wondering, perhaps the the CPU is just scrambled. when i was a kid, i used to love deliberately crashing it to get some insanely bizarre sounds happening. Anyway, I changed the battery, which of course resets the memory - the existing one was actually new-ish, but had already started corroding. I put in a Ni-MH, but a lithium would probably be better... at least it shouldn't leak again.

my problem now is - do I reload the original patch data or not? because some of the randomly generated patches sound awesome - and impossible to recreate, as they often include impossible or out of range parameter data.

happy camper.
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Re: Korg Poly-61 fix

Postby Hookemeister » Thu Jun 21, 2012 2:45 pm

my problem now is - do I reload the original patch data or not? because some of the randomly generated patches sound awesome - and impossible to recreate, as they often include impossible or out of range parameter data.


Hi Wez

Never had a Poly-61 but on my DW-8000 you just:

1: Patch from the "TO TAPE" mini jack to anything that will record a wave file

2: Switch the "TAPE" switch to "ENABLE"
You should now see 7A PE on the alpha numeric display.

3: Adjust the record level on your soundcard or whatever you're recording into.

4: Start recording and and after 5 seconds press the "SAVE" button on the Poly.
The display should now show SA uE

5: When the display reverts to 7A PE the Save Data process is finished.

I usually record it a couple of times just to be safe.

If the above applies to the Poly-61, let me know and I'll send you instructions on the "VERIFY" process and the "LOAD" process.

Hope this helps.
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Re: Korg Poly-61 fix

Postby Futureman » Thu Jun 21, 2012 4:57 pm

wez wrote:....some of the randomly generated patches sound awesome - and impossible to recreate, as they often include impossible or out of range parameter data.

.


I remember the same thing.. I made some patches that sounded huge and, only to find some of the pitch parameters were out of range..

Surprisingly fat synth.
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Re: Korg Poly-61 fix

Postby Thirteen » Thu Jun 21, 2012 8:21 pm

Don't put a lithium battery in there unless you remove the diode that allows the battery to charge or you will be picking pieces of battery from all over the insides of the machine.
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Re: Korg Poly-61 fix

Postby wez » Thu Jun 21, 2012 9:57 pm

thanks greg... i'm actually using my phone to store and load the tape data - how's that for a 21st century solution!? and yes the procedure sounds pretty much the same as the DW8000.

and good advice about the lithium battery, thanks steve... I remember reading that, but it's exactly the sort of thing I would forget about!

I don't have any immediate plans to put a midi kit in - will probably do the filter/cutoff knob mod first - but what kit would you guys recommend? i've never done a midi retrofit before.
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Australian importer of Crumar Mojo keyboards & accessories. Vintage keyboard fetishist.
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