Korg Poly61 Refurb

So over a year ago or so, a friend of mine, Kyle, traded me an old, beat up Korg Poly61 (what is my deal with broken korgs?).   So it had some weird issues he told me about.  Like every 6th voice would be out of tune and the keys would work sometimes.  Well I ended up getting the thing home, and it worked perfectly, but would intermittently freak out.  I had a ton of other projects at the time so I never really got around to looking at it until last week.  And let me tell you, there was a lot to look at.  So I powered up the poly61 for the first time in almost a year, and not too much happened.  Most of the keys didn't work.  I managed to get a couple notes programmed into the chord memory, and then stuck it on the arpeggiator.  I didn't have any problems with any voices out of tune, but after running through the parameters, I found that one of the filters wasn't working.  This sucked, because the filters were made from OTAs not single chips like in the poly6 or the DSS-1/DW8000 (all SSM stuffs).  The Envelopes are SSMs, but not the filters.  I have actually heard that it is based on the MS-20 filter, but it sounds too mellow to be an MS-20 filter.

After doing some reading, I couldn't find a lot about missing filters, most people just blabber about the notorious battery issues.  These old synths with memory have batteries that have a lovely habit of exploding all over the circuits, and the electrolyte then dissolves everything in its path.
This poly61 did not have this problem.  All the chips looked fine with no signs of corrosion.

I did a fairly stupid test though and decided to wiggle around many of the jumper wires going between voices.  I noticed that one would intermittently get the filter working.  These old jumpers seem to have a tendency of degrading over time.  I need to replace the wire still, but I think I might just go through and do all of them.  I replaced a couple, and plugged it all back in, but something weird happened!

A voice was out of tune!  Just like Kyle had said!

But where the hell did this come from.  I was starting to believe that every time I would turn it on would be a new problem.  I found it was just a loose connection internally.  This connector may be need replaced, but I'll save that for later.

So the next job on the list is to replace all the jumpers in this old guy, I hope it cleans up the "consistency" of the synth.


So tonight, I decided to tackle the next problem: the keyboard not working.  The keyboard had worked perfectly before, but it seems that it, as all the other connections, were intermittent.  80s keyboards had many different switch contact types.  The DW uses rubber contacts.  The Ensoniq Mirage uses these weird, and super-damn-annoying springy things.  They give for a nice action, but have many temperamental problems.  The poly61 uses similar, classic rubber contacts.  The type with the small rubber nipple-things with a conductive silicone underside.  Well this conductive silicone doesn't stay conductive for very long.  The carbon wears off over time.  No deoxit or alcohol or cleaner will fix it.  Once they are dead, they are dead.  I have seen some pretty nifty solutions, but none have ever been very practical, and most people just resort to completely replacing the contact strips.
Last summer I experimented with a couple ways to fix this.  I had a Roland MC 909 I picked up on the cheap on Ebay that was "untested".  Well it was certainly.  It would boot up, but none of the rubber pads would work, minus pause and a couple random ones.  I checked the actual metal contacts on the motherboard with some tin foil, and they were responsive.  I had seen this CircuitWriter stuff at RadioShack and though hmmmmm.  The stuff is expensive.  It is 20 bucks for a little pen with some conductive, silver based ink in it.  The nifty thing is, it sticks to silicone rubber really well.  It takes a couple days to dry on to the rubber for a semipermanent solution, but I decided to test it out.  I applied the stuff, waited 48 hours and put the pads into the MC 909.  All the pads were beautifully responsive, almost more so that previous!  I was pleased with this finding.

Now I am doing this again.  I just coated all 61 rubber contacts, and am letting them bake on a couple days.  I tested one, and the keys work beautifully.  I hope to seal up the poly61 this weekend, clean up the case and the switches and get it on a keyboard stand.