<div dir="ltr">Forwarding here because I feel like this is the better audience to help diagnose korg polysix issues. Quick recap:I have already replaced the cpu board and psu with a synthronicss kit.. There's still noise, which sounds like this:<div><br></div><div><blockquote type="cite"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><span class="gmail-Apple-converted-space"> </span><a href="https://drive.google.com/file/d/14MpNs5ZL6Ze7kJ5bgBbiDW5y5Eahphe3/view?usp=drivesdk" rel="noreferrer" target="_blank">https://drive.google.com/file/d/14MpNs5ZL6Ze7kJ5bgBbiDW5y5Eahphe3/view?usp=drivesdk</a><span class="gmail-Apple-converted-space"> </span></blockquote></div></blockquote></div><div><br></div><div>After signal tracing, The audio gets corrupted from pins 13 and 14 of IC3 - the BBD chip (schematic markup<span class="gmail-Apple-converted-space"> </span><a href="https://drive.google.com/file/d/1EtCYwnFEMezC66sSAfGkpFU43KHTWbZq/view?usp=share_link" target="_blank">here</a>)<div><br><b>however</b>!<br><br>I also see noise showing up on clock input of the same chip (pin 2). Any time I hear noise, I see it on that pin as well. It is worth noting this noise does not appear on any of the other clock or audio pins of the other BBD chips (IC1 and IC2). This leads me to think the problem is localized to<span class="gmail-Apple-converted-space"> </span><a href="https://drive.google.com/file/d/1rWWEkdib_zFsCpb0En-btTF-ttP-CbEU/view?usp=share_link" target="_blank">this area</a>.</div><div><br> <i><font color="#0000ff">Basic Question #1: How likely is it that the BBD chip is actually fine and what I'm hearing is caused by passing noise through the clock input?</font></i><br><br>Assuming that's possible, I can trace the noise farther upstream all the way back to IC23, an LM324.</div><div> </div><div>While investigating I found several resistors with the same kind of green corrosion on thier leads in this portion of the circuit. The above picture has the corroded resistors highlighted in red,with suspicious resistors highlighted in orange. These are resistors R133, R172, and R199-204. All showed the same kind of visible corrosion as seen near the battery, but on a completely different board. Makes me wonder where else this may have migrated to. Replacing these resistors did put a dent in the persistence and frequency at which the noise appears, but it's not gone.</div><div><br><i><font color="#0000ff">Basic questions #2: Could a corroded resistor cause or contribute to this problem?<br></font></i><font color="#0000ff">Basic question #3: It makes sense that a bad chip would cause noise on its output, but is it possible it could spit out noise through its inputs?</font></div><div><font color="#0000ff"><br></font>IC23 is the first thing control signals see coming over from the KLM-367 control board (Other than the nearby resistors). This noise issue existed before I replaced the controller board with the one from synthronics so I highly doubt the issue is coming from the there....unless the CPU chip is messed up? I do remember it having corrosion on its pins as well. But the synth plays and behaves as I'd expect.<br><br></div><div>I'll read back through some messages to see if I can rule more things out or address any questions. thanks!</div></div><div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">---------- Forwarded message ---------<br>From: <strong class="gmail_sendername" dir="auto">Jimmy Moore</strong> <span dir="auto"><<a href="mailto:jamoore84@gmail.com">jamoore84@gmail.com</a>></span><br>Date: Wed, Mar 25, 2026 at 10:22 PM<br>Subject: Re: [AH] diagnosing polysix output noise - was Korg Polysix: CPU board replacement options?<br>To: Florian Anwander <<a href="mailto:fanwander@mnet-online.de">fanwander@mnet-online.de</a>><br>Cc: AH send <<a href="mailto:analogue@hyperreal.org">analogue@hyperreal.org</a>><br></div><br><br><div dir="ltr">Thanks to everyone who reached out with tips and well wishing! The audio signal path gets corrupted from pins 13 and 14 of IC3 - the BBD chip (schematic markup <a href="https://drive.google.com/file/d/1EtCYwnFEMezC66sSAfGkpFU43KHTWbZq/view?usp=share_link" target="_blank">here</a>)<div><br><b>however</b>!<br><br>I also see noise showing up on clock input of the same chip (pin 2). Any time I hear noise, I see it on that pin as well. It is worth noting this noise does not appear on any of the other clock or audio pins of the other BBD chips (IC1 and IC2). This leads me to think the problem is localized to <a href="https://drive.google.com/file/d/1rWWEkdib_zFsCpb0En-btTF-ttP-CbEU/view?usp=share_link" target="_blank">this area</a>.</div><div><br> <i><font color="#0000ff">Basic Question #1: How likely is it that the BBD chip is actually fine and what I'm hearing is caused by passing noise through the clock input?</font></i><br><br>Assuming that's possible, I can trace the noise farther upstream all the way back to IC23, an LM324.</div><div> </div><div>While investigating I found several resistors with the same kind of green corrosion on thier leads in this portion of the circuit. The above picture has the corroded resistors highlighted in red,with suspicious resistors highlighted in orange. These are resistors R133, R172, and R199-204. All showed the same kind of visible corrosion as seen near the battery, but on a completely different board. Makes me wonder where else this may have migrated to. Replacing these resistors did put a dent in the persistence and frequency at which the noise appears, but it's not gone.</div><div><br><i><font color="#0000ff">Basic questions #2: Could a corroded resistor cause or contribute to this problem?<br></font></i><font color="#0000ff">Basic question #3: It makes sense that a bad chip would cause noise on its output, but is it possible it could spit out noise through its inputs?</font></div><div><font color="#0000ff"><span><br></span></font>IC23 is the first thing control signals see coming over from the KLM-367 control board (Other than the nearby resistors). This noise issue existed before I replaced the controller board with the one from synthronics so I highly doubt the issue is coming from the there....unless the CPU chip is messed up? I do remember it having corrosion on its pins as well. But the synth plays and behaves as I'd expect.<br><br></div><div>I'll read back through some messages to see if I can rule more things out or address any questions. thanks!</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Mar 16, 2026 at 3:31 AM Florian Anwander <<a href="mailto:fanwander@mnet-online.de" target="_blank">fanwander@mnet-online.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<p>the signal tracker aside</p>
<p>I assume it is not related to a certain voice. So assumingly it
is the summing amp on the mainboard or something on the chorus
board. Does it depend on the on/off-setting of the effect section?
If not then there are only a few parts that remain as suspects. </p>
<p>And just as remark: many people forget, that there is a VCA on
the effect board that is controlled by the resonance setting. So,
if the noise depends on the resonance setting, you can narrow down
the source quite well.</p>
<p>Florian</p>
<p><br>
</p>
<p><br>
</p>
<div>Am 15.03.26 um 19:22 schrieb Jimmy
Moore:<br>
</div>
<blockquote type="cite">
<div dir="ltr">d'oh, definitely should have thought of the signal
tracer sooner! Thanks for the reminder.</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, Mar 15, 2026 at
7:57 AM Bob Grieb <<a href="mailto:rlgrieb1@verizon.net" target="_blank">rlgrieb1@verizon.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Hello,<br>
<br>
A transistor or op amp that has failed can cause the sort
of<br>
noise you are hearing. One way to track down the source is
with a<br>
"signal tracer", which is just an amplifier and speaker.
Usually capacitor<br>
coupled input, since the point you are probing may have DC
voltage on it.<br>
A small cap, something like 0.1uF should be usable. You
would connect<br>
the ground lead of the amplifier input cable to ground at the
Polysix.<br>
The signal input lead would feed through the cap and into the
amplifier.<br>
Then you can touch various points in the circuit to see which
ones have the<br>
noise and which don't.<br>
<br>
Another technique that helps for this type of problem is
circuit <br>
cooling spray.<br>
You just spray various semiconductor devices in the signal
path to see <br>
if the<br>
noise changes when you cool any of them. Just one second of
spray on each<br>
device is plenty.<br>
<br>
Bob Grieb<br>
<br>
On 3/15/2026 9:16 AM, Jimmy Moore wrote:<br>
> Thanks for everyone's earlier feedback. I ended up
getting a <br>
> replacement processor board and power supply from <a href="http://synthronics.de" rel="noreferrer" target="_blank">synthronics.de</a> <br>
> <<a href="http://synthronics.de" rel="noreferrer" target="_blank">http://synthronics.de</a>>
which has helped me sleep a lot better<br>
><br>
><br>
> With those failure modes addressed, there's now a noise
issue to <br>
> solve. Here's a short recording from the bench speaker<br>
><br>
> <a href="https://drive.google.com/file/d/14MpNs5ZL6Ze7kJ5bgBbiDW5y5Eahphe3/view?usp=drivesdk" rel="noreferrer" target="_blank">https://drive.google.com/file/d/14MpNs5ZL6Ze7kJ5bgBbiDW5y5Eahphe3/view?usp=drivesdk</a>
<br>
> <<a href="https://drive.googlecom/file/d/14MpNs5ZL6Ze7kJ5bgBbiDW5y5Eahphe3/view?usp=drivesdk" rel="noreferrer" target="_blank">https://drive.googlecom/file/d/14MpNs5ZL6Ze7kJ5bgBbiDW5y5Eahphe3/view?usp=drivesdk</a>><br>
><br>
> This does not seem to be affected by any panel controls,
system <br>
> settings, or bank presets.<br>
><br>
> The noise is most prominent when playing notes, but
there's also that <br>
> lowish rumble when silent. more prominent on the phones
output if that <br>
> helps.<br>
><br>
><br>
> Is this a telltale sign of anything in particular?<br>
><br>
><br>
><br>
><br>
><br>
> On Fri, Feb 27, 2026, 5:36 PM Jimmy Moore <<a href="mailto:jamoore84@gmail.com" target="_blank">jamoore84@gmail.com</a>>
wrote:<br>
><br>
> You can get a new case, too! 😂<br>
><br>
> <a href="https://reverb.com/item/93243657" rel="noreferrer" target="_blank">https://reverb.com/item/93243657</a><br>
><br>
> On Fri, Feb 27, 2026, 3:44 PM Tim Parkhurst<br>
> <<a href="mailto:tim.parkhurst@gmail.com" target="_blank">tim.parkhurst@gmail.com</a>>
wrote:<br>
><br>
> So, besides the knobs and the end cheeks,
everything on the<br>
> PolySix needs to be replaced.<br>
><br>
> Got it.<br>
><br>
><br>
> Tim (embraceable, replaceable me) Servo<br>
> ---<br>
> "Imagination is more important than knowledge." -
Albert Einstein<br>
><br>
><br>
><br>
><br>
><br>
> On Fri, Feb 27, 2026 at 2:09 PM DJ Maytag
(DJMaytag)<br>
> <<a href="mailto:djmaytag@djmaytag.com" target="_blank">djmaytag@djmaytag.com</a>>
wrote:<br>
><br>
> It certainly is the easiest, but it is an
expensive board.<br>
> I did one a few years ago, with the Kiwisix
PSU upgrade,<br>
> and then had to get a replacement panel board
from<br>
> Synthronics.de <<a href="http://Synthronics.de" rel="noreferrer" target="_blank">http://Synthronics.de</a>> since
the one panel<br>
> got some sort of acid/gas all over the bottom
side of it.<br>
> I think it’s worth springing for the
SynthGraphics.com<br>
> <<a href="http://SynthGraphics.com" rel="noreferrer" target="_blank">http://SynthGraphics.com</a>> overlay
for all the added Kiwi<br>
> functions. IIRC it’s about $129, and is well
worth it if<br>
> your top panel is scratched up (it cover
almost all the<br>
> panel surface).<br>
><br>
><br>
><br>
>> On Feb 27, 2026, at 10:00 AM, Jimmy Moore<br>
>> <<a href="mailto:jamoore84@gmail.com" target="_blank">jamoore84@gmail.com</a>>
wrote:<br>
>><br>
>> *tl;dr*: is kiwi the best option?<br>
>><br>
>> I got a korg polysix for $100 recently
and it is<br>
>> suffering from the usual creeping
corrosion. Several<br>
>> list members have battled this in the
past with some<br>
>> common takeaways:<br>
>><br>
>> Tom Wilshire<br>
>><br>
>> The Polysix has a lot of reliability
problems, but<br>
>> aside from the keyed and the panels
switches, *most<br>
>> of them stem from corrosion on the
main board.*<br>
>><br>
>> Brianw<br>
>><br>
>> A local musician brought me a Polysix
that had had<br>
>> repairs made to 'fix' a previous
battery leak. That<br>
>> old repair had failed. We gave the
internet advice a<br>
>> chance, and soaked the board in
vinegar to neutralize<br>
>> the acid, but that effort did not pan
out. The<br>
>> batteries are still available, but
that doesn't help<br>
>> if the CPU board is less than 100%<br>
>> *The solution was a Kiwitechnics
Kiwisix board, and<br>
>> the added benefit is that this old
Polysix now has MIDI.*<br>
>><br>
>><br>
>> and KennyBalys<br>
>><br>
>> I have repaired this board annually
with success :)<br>
>> One could say, I derive a lot of self
esteem from my<br>
>> repairs, in doing them correct. The
board itself,<br>
>> visually, looks like a very nicely
repaired<br>
>> board that, once upon a time, had
some damage. It<br>
>> looks nice enough to<br>
>> sell, if I had a lack of moral fibre
(its going to<br>
>> re-cycling)<br>
>> This problem keeps on re-occuring.
Corrosion<br>
>> appearing inches away from<br>
>> where the original damage occured. I
can repair it<br>
>> again now, it will<br>
>> likely be off again next year.<br>
>> Perhaps some of the PC boards from
that era were more<br>
>> fibrous than<br>
>> others?<br>
>> *As of now, I will no longer attempt
repairs on the<br>
>> Polysix CPU board.<br>
>> Replacement only.*<br>
>><br>
>><br>
>> I am aware of the Kiwi main board + PSU
mods. I have<br>
>> also heard of people having good
experience with<br>
>> Synthronics.de as recently as 2022, but I
can't find them<br>
>> online.<br>
>><br>
>> Are there any other options to consider?<br>
><br>
<br>
<br>
<br>
-- <br>
This email has been checked for viruses by Avast antivirus
software.<br>
<a href="http://www.avast.com" rel="noreferrer" target="_blank">www.avast.com</a></blockquote>
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