Discussion about the Korg PolySix synthesizer

No, I'm not trying to flatter anybody.  I understand that I made lots of mistakes. IC16 might have been a botched attempt to salvage a part for another project.  Who knows, maybe I gave up or got a phone call or something and forgot about it.  I'm pretty sure that Mouser or Digikey put the wrong cap in the bag.. he he.   Mistakes are part of learning.  I just corrected a buddy's mistake over the weekend.  He made the classic mistake of putting the PSU caps in backwards on an RS202.  Sometimes a second opinion can make all of the difference in the world.

Also, to folks that are attempting this:  I'm pretty good at soldering and have a Hakko 703b which is one hell of a soldering station.  I also have the best analog scope ever, Tek 2465, and a good multimeter.  It is very easy to make mistakes and the decimal error on the tape engage really screwed me up.

All together, I think I spent about 8 hours on this project from ordering the board and parts, populating it, and testing:(  Furthermore, it took me an entire year to finally get it running because I put it aside after making the initial mistakes.

-Mike

--- In PolySix@yahoogroups.com, "backshall1" <backshall1@...> wrote:
>
> Unfortunately, both the calibration problem and MG bleedthrough are
> happening on the new clone board, not an old damaged board. It's not the
> first time I've seen new boards that wouldn't calibrate, either. Generally,
> the 4 and 8 lights come on and you can change the 8 to 7, 6, 5, but you
> can't make the 4 move down. I tried a couple of different types of DAC08 and
> even an original spec 1408 but it made no difference. I also tried a 4560 in
> place of the TL072.
> 
>  
> 
> I did lift one end of R9 to verify that the MG leak was on this trace from
> CN06-2 to R9. The only way I can see this happening on a new board is if
> there is contamination on the bottom of CN06 between pins 1 and 2 that needs
> to be cleaned up, since the old Molex connector was moved from the old to
> new board and the area around CN06 is a real mess on the old board. I know
> it's a pain to remove these headers, but for a new board it makes more sense
> than cutting the trace.
> 
>  
> 
> I think all Mike's flattery was an attempt to bribe me into not mentioning
> the other problems found on his new board. Ha, I warned you. This is for
> "educational purposes" for the rest of us trying to build new boards.
> 
>  
> 
> 1)       Blown fuses - solder bridge between C6 and C7. Although these two
> capacitors each have one pin connected to ground, the pins closest together
> are not ground, they are +15v and -15v. It might seem like a bad design to
> have these two pins so extremely close together but I guess it's the best
> way to get +15/-15 rails down to all the op-amps and comparators.
> 
> 2)       D4-D7 unstable, no control from sub octave switch - No solder on
> ground pin of IC29.
> 
> 3)       No MG at all, no Effects Speed control - Several pins not soldered
> on IC16.
> 
> 4)       From Tape not working - C4 had a 47nF (47000pF) cap in it instead
> of 470pF.
> 
>  
> 
> Missing some IC socket pins while soldering is an easy thing to do with all
> those shiny pins on a shiny new board and is not as easy to find as you
> might think. I didn't notice these until I got it under a big lighted
> magnifier.
> 
>  
> 
> Don B.
> 
>  
> 
>   _____  
> 
> From: PolySix@yahoogroups.com [mailto:PolySix@yahoogroups.com] On Behalf Of
> klosmon
> Sent: Thursday, October 13, 2011 2:47 PM
> To: PolySix@yahoogroups.com
> Subject: Re: [PolySix] Don Backshall is a great guy!!
> 
>  
> 
>   
> 
> Nice guy, indeed.
> 
> Two things:
> first, I've encountered many old 367 boards that were incapable of D/A 
> calibration (as specified in the service documents) that still worked 
> fine -- this is probably not an issue.
> 
> Second -- regarding the MG bleedthrough...
> I've encountered this on many battery-damaged boards; it has to do with 
> damaged traces bleeding through to each other.
> A fix I've found that works 99% of the time: cut the trace on the 
> bottom of the board at CN06-2, and also the trace that goes to R9 (near 
> CN05). Cutting the trace at both ends eliminates any possibility of the 
> mod signal being affected by adjacent traces. The mod bleedthrough 
> should disappear. Now solder a jumper between CN06-2 and the end of R9, 
> and hopefully the mod function will work, without distortion or other 
> problems.
> 
> ~GMM
> 
> Mike wrote:
> > 
> >
> > Don Backshall solved all of my PolySix issues and did it for basically 
> > a handshake. Furthermore, he mailed my KLM-367 board back to me in 
> > good faith before my PayPal payment even cleared!!! I sent him as much 
> > extra money as I could because he really deserved it. Here's the 
> > correspondence bleow:
> >
> > If the e-mail below can't restore your faith in blind internet 
> > transactions, I don't know what will.
> >
> > (Don's Response October 6)
> >
> > Okay, the boards are on their way back. Priority Mail with delivery 
> > conf # 03103490000077720492.
> > Still three problems that I am aware of:
> > 1) D/A calibration - Can't get the right lights to come on, but seems 
> > to be in spec anyway.
> > 2) MG leak - I'm assuming this is caused by some crud between pin 1 
> > and 2 on the bottom of CN06 header. I know these are a pain to remove, 
> > but I think it needs to be done. Sounds really bad when it's cold. 
> > Gets a little better when it warms up.
> > 3) MG delay - Known problem with 2N3904 in Q5 position. Using the 
> > (2SC945) transistor from the old board seems to fix this, but the pins 
> > are different. You can compare what's connected to what between old 
> > and new boards to see what pin goes where. One of my old boards had a 
> > 2SC2785.
> >
> > $8.60 postage
> > $1.60 fuses
> > $0.15 capacitor
> > -----------------------
> > $10.35 grand total - You can send it to this Paypal acct 
> > backshall1@... <mailto:backshall1%40bellsouth.net>
> <mailto:backshall1%40bellsouth.net>
> >
> > I'm pretty sure you can get this board sounding just like it should, 
> > even if you can't get the right calibration lights to come on.
> > Have fun,
> > Don Backshall
> >
> > _______________________________
> >
> > (my response to him solving my problems October 05)
> >
> > That's great!! It looks like I'm a decimal doofus! Ha Ha. What's the 
> > bill? I can send you a PayPal payment today or tomorrow. I'll praise 
> > your expertise on the Korg PolySix forum too if you're intersted.
> >
> > Thanks again,
> >
> > -Mike
> >
> > 
> 
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