[sdiy] Poly 61 near death?

[Bob Weigel]

Yeah the vinegar would probably be a good thing.  Don't have any around. 
Salsa? :-)

Umm..yeah I have a good multi-trak and a good poly-61.  Actually there 
are some good sounds the poly is capable of but I love the Multi-trak. 
Certainly no comparison.  I have actually an MT, six Trak which I also 
love (almost identical but both with their quirky cool differences.  The 
six is actually great for some special fx sounds and the multi is just a 
great velocity sensetive analog!)  Oh and I have another REALLY nice 
Split-Eight I might put on ebay soon.  I wrote a whole bank of sounds 
for it on vacation last month and those are on my website now.  I just 
don't need all of them and I'm not going to lose the MT and the six was 
my first and is the first multi-timbral so it's great for a museum 
piece.  Split-Eight is..well the most compact 8 voice real vco synth 
and...hmm... yeah I think it's got to be the one to go.  Besides it's 
near mint and I can probably get a good chunk out of it.

ANyway...the contacts.  I recommend a proceedure I've tried many times.  
Acetone as recommended by organ repairman friend of mine Andy Seitz.  
I've done it many times now and it usually works and NEVER have I seen 
it make things worse.  I actually take a 'depth resistance profile' with 
some sharp probes and I can tell exactly how the blooming things are 
going to respond.  The acetone always makes them better.  Over years of 
service I've never seen a repeat problem whent he treatment works....but...

There is occasionally one how and then where it will NOT work.  My best 
theory to date is this

1) the Acetone reacts with the surface rubber and allows a thin layer to 
degenerate and abrase off

2) the reason they won't contact is the rubber adheres together and the 
microscopic conductive material that is part of it does not.  So as 
these things wear, the conductive stuff can basically get 'banged out of 
it'.  So 1) is a good thing because the acetone most certainly does NOT 
react with conductive material :-)  Thus it 'levels the playing field' 
again.

3)OCCASIONALLY I think I run into one where in the process the thickness 
of the conductive 'slurry' or whatever wasn't very deep or the 
concentration fell off at depth to where there isn't enough conductive 
material to create a low enough resistance across the contacts to work 
well or like that.


But ..usually the process works well.  The carbon I'm sure would work 
temporarily but...I would think it would get scattered after a bit of 
hard playing.  Hmm.

Another technique I might try..the problem with a lot of conductive add 
on materials is that nothing likes to stick to this stuff!  But hey, how 
about taking a dremel and drilling with like a number 65 bit or 
something through roughly the middle of the rubber contact....then put a 
drop of something like nickel print there :-)  Thattttt might do it.  
Because then it's like...digging a post hole ya know :-).  Sometimes it 
might be worth it.  It's a thought. -Bob

Travis Shire wrote:

>to scrub everything clean with alcohol or maybe there's a better
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> solvent for the battery acid..I dunno. ANyone?
>
>After cleaning the affected area, white vinegar does a good job of putting
>the kaibosh to the acid and stopping the spreading. Rinse after the vinegar
>treatment. I recently gutted a poly-61 because of *severe* acid damage. Its
>now a diy project donor. It was so bad the gas from the battery crept up one
>of the cables from one end to the other....nasty stuff. AFAIK, the poly 61
>shares little with a multi-trak...especially sound quality (poly-61s are
>yucky sounding).
>As far as keys not responding, graphite powder (make yer own with some
>sandpaper and a pencil) rubbed into the carbon pad contacts (keyswitches)
>fixes that problem....had to do it with my poly-61 project board, worked
>great. Also, do a test to find the pencil laying around that has the highest
>carbon content (will have the lowest resistance)...it'll work better. I just
>made thick scribble paths on some paper and took the meter to each path to
>measure resistance. Don't laugh.....it beats buying conductive epoxy or a
>circuitworks pen.......
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