Discussion about the Korg PolySix synthesizer

Have you looked at any of these lines with a scope?  It's the fastest & 
easiest way to see what's going on, and narrow down the problem areas.
~G

On 12/3/2014 9:10 AM, backshall1@bellsouth.net [PolySix] wrote:
>
> Yes, those old CMOS chips do seem to have a definite shelf life. I\u2019ve 
> seen a few dead 4051 chips in Polysix synths over the past few years. 
> For that first problem, it sounds like it could be either on the mux 
> side or the demux side and there are a couple of 4051 chips on each 
> side. For such a similar sounding problem on both PW and Cutoff, I 
> would expect it to be caused by a component that is common to both 
> settings though, and PW goes through KLM-369 IC2 on the multiplexer 
> side and KLM-367 IC19 on the demultiplexer side , while Cutoff goes 
> through KLM-370 IC1 on the multiplexer side and KLM-367 IC18 on the 
> demultiplexer side. Nothing common there. Are there other knobs 
> affected? It might be a problem with the chip select logic, like an 
> old 4011 getting slow.
> Don Backshall
> *From:* mailto:PolySix@yahoogroups.com
> *Sent:* Wednesday, December 3, 2014 11:12 AM
> *To:* PolySix@yahoogroups.com <mailto:PolySix@yahoogroups.com>
> *Subject:* Re: [PolySix] fully recapping a vintage synth
>
> High pitched whine could be old 4000 series logic chips. Similar sound 
> ie. 4-5KHz whine arises on Yamaha CS50-80s, and is usually down to the 
> logic chips on the CPU card.
>
> A recap (when done well) is never a bad thing. At least it will 
> improve the sonic characteristics, at best it will yeild improvements 
> in all aspects of operations. It's never a bad place to 
> start...especially if the synth has spent a long time switched off, 
> and forgotten.
>
> On Wednesday, December 3, 2014, jim@saltlands.com 
> <mailto:jim@saltlands.com> [PolySix] <PolySix@yahoogroups.com 
> <mailto:PolySix@yahoogroups.com>> wrote:
>
>     Understandable concern. This is a general question with the
>     assumption that we're all knowing what we're doing, and with a
>     curiosity specifically toward analog synths 30+ years old or so.
>
>     I myself have done a lot of recapping doing tape machine
>     restoration, so am comfortable doing full scale recap overhauls of
>     units.
>     My polysix has a couple minor sonic issues that creep up now and
>     again, and sometimes i have the urge to just put all new caps in
>     and go from there. Sometimes this ends up solving problems, and at
>     worst it just spends a handful of hours of my own time and a few
>     bucks on caps and you get a freshly capped machine.
>     One of the issues is I've got some strange grounding issue related
>     to a multiplexer, i believe. It may be a faulty multiplexer or it
>     may be a component connected to said multiplexer. The symptom is..
>     on a handful of pots, when i turn them they emit a sound like a
>     square wave if turned at the right pace/quick enough. Sounds
>     exactly like each digital point in the pots signal sent is somehow
>     making this noise. So if you turn it slow, you can not hear it at
>     all because the rate of it happening is low.
>     https://soundcloud.com/circuitsynth/polysix-knob-sound
>
>     My other issue is more strange.. a high pitched sustained
>     frequency arises sometimes in certain conditions unknown, and only
>     goes away when you press either A, another note far away from the
>     range of the previous note (ie up high or up low) or B, you hit
>     the Chord Memory or Hold switch, sometimes one or the other. This
>     pitch arrives once or twice every hour of playing. But it goes
>     away fast if you hit the right thing.
>
>     This second problem is much more vague to me and perhaps a recap
>     will address it. Could it be a decoupling cap somewhere failing?
>     The pitch is the same exact every time. it's like 4kHz or 5kHz,
>     around there.
>
>     I also like synths to be as least noisy as possible, so this is
>     another case for recapping. I've already bypassed the effects
>     section with a direct output and it's a huge improvement, but i
>     still hear a need for it to be even better.
>
>