Sorry to revive this old thread, but it doesn't seem to address the VCA problem, only the LFO-to-VCO bleedthrough problem. TP5 on one of my Polysix's definitely shows some LFO signal getting through, even though MG Level is set to 0. If the 3-way MG Mod switch is set to VCA, it reduces the unwanted signal quite a bit. If it's set to VCO or VCF, the LFO leakage to the VCA is very noticeable. This could be a bad IC1 14066 or leakage on the trace somewhere between IC1 and CN03-5. I don't have any 14066 chips around to test this so I was wondering if others have had any experience fixing this with either cutting the trace and adding a wire, or is it likely to need a new IC1? Too bad there is no easy way to lift an IC pin. Maybe I can try lifting one end of R190 over on the KLM-368 board and running a test jumper to it from KLM-367 IC1 pin 4.
As a side note, I just got around to lifting one side of R9 on the KLM-367. What a difference! Not only did it get rid of the slight LFO leak to the VCO, it cleaned up the sound tremendously. Apparently there was quite a bit of random noise on this trace that gave the whole sound a very raspy edge that wasn't really that noticeable until it was gone. With the jumper in from CN06-2 to R9, and the board trace cut at both ends, it sounds great. This eliminates C43, which may have been bad anyway considering the sound. Are there any opinions as to whether C43 should be added to the new jumper at either end, or maybe using a shielded wire grounded at one end for this jumper?
Thanks,
Don B.
--- In PolySix@yahoogroups.com, klosmon <klosmon@...> wrote:
>
> mborish_2000 wrote:
> >
> >
> > That solved it.
> >
>
>
> OK. To restore the mod circuit without the noise:
> On the bottom of the CPU board, cut the trace from pin 2 of CN06;
> solder a wire from pin 2 to the free end of R9 (the resistor previously
> desoldered).
> The correct end is the one closest to CN05.
> This should restore all VCO mod functions, without the bleed through.
>
> > Thank you so much Klosmon. Unsuprisingly, I discovered another problem
> > after the first one. My Effects section is always engaged and is
> > producing some strange ring modulation type sounds depending on the
> > value of the speed/intensity knob. Is this related to the first problem?
> >
>
>
>
>
> As Andrew stated in another post, this is probably due to an incomplete
> battery leak repair job.
> Could be a latch, data line, etc.
>
> ~GMM
>
> >
> >
> > -Mike
> >
> > --- In PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com>,
> > klosmon <klosmon@> wrote:
> > >
> > > One frequent problem with the CPU board can cause unwanted
> > modulation of
> > > the VCO, which can sound like what you're describing.
> > > To see if this is the case, get a soldering iron & lift one end of R9,
> > > which is a 10K resistor located between IC8 and CN05.
> > > This will disconnect all modulation to the VCO; if it eliminates the
> > > problem, let me know, and I'll describe where to go f rom there.
> > >
> > > ~GMM
> > >
> > > mborish_2000 wrote:
> > > >
> > > >
> > > > I've got a few problems that I can't figure out. Unfortunately, my
> > LFO
> > > > is bleeding into the VCA? and I can't figure out a way to stop it.
> > > > It's not a violent bleed but it's enought to make the Polysix
> > > > unusable. If I turn all of the controls down, it is still there. All
> > > > of the controls are functional. All of the potentiometers test out
> > OK.
> > > > I tested all cables for continuity. I cleaned the LFO modulation
> > > > select switch and replaced the 4051 on KLM 369 without any luck. I
> > > > read somewhere that somebody suggested cutting a trace, but they
> > > > couldn't remember enough details about what they did. I didn't see
> > any
> > > > calibration proceedure related to the LFO modulation either.
> > > > Everything else works fine.
> > > >
> > > > Does anybody have any suggestions? Logic and microprocessing are
> > > > really beyond my knowledge.
> > > >
> > > > -Mike
> > > >
> > >
> > >
> > > >
> > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
> >
>
>
>
> [Non-text portions of this message have been removed]
>