Discussion about the Korg PolySix synthesizer

Hello everyone
I'm Bastien from France, currently living in Spain.
Today I begin to repair my polysix. I've done a quick check on it, here are the problems I've seen:

KLM 367 : Battery leakage
KLM 366 : Voice 3 doesn't make any sound
KLM 369 : Octave, waveform, PW/PWM, PWM speed and sub osc pots and switchs doesn't affect the sound in anyway. Will check the whole card, connectors, traces etc

I'll try to give some news time to time.

For the voice problem:
I' ve swapped 2056 and 2044 from a valid voice but the voice 3 is still mute

Has someone a lead to help me fixing this ?

Regards

Bastien

Bonjour (ou "buenas dias"?) Bastien,

> KLM 367 : Battery leakage
>

The first thing before you continue with anything else: desolder all IC
is a wide range around the battery, clean the board, test each trace
with a beeper and - if required resolder the traces or fix them with wires.
Then solder-in IC sockets and insert new ICs. Don't use the original ICs
any more - the battery acid already has crept into them and will kill
them some years later.

As sockets please use the good industrial style ones with round
receptors like these:
https://cdn-reichelt.de/bilder/web/artikel_ws/C130/GS_20P.jpg. Do not
use these https://cdn-reichelt.de/bilder/web/artikel_ws/C130/GS_20.jpg
with only a single spring receptor.

I replaced all ICs from the left boarder up to IC23/24. The CPU cannot
be replaced, but you still should desolder it, and socket it. Also
replace the diodes in that area.
The ICs and sockets are dirt cheap. You won't spend mor than 25 Euros.
But it will be a hell of work.

You need a electronic desoldering station. Do not use a mechanical
desoldering pump. A mechanical pump will destroy the traces which are
already weakened from the battery acid.


Unless you did not do this, you don't have to continue.

> KLM 366 : Voice 3 doesn't make any sound
>

This has nothing to do with the battery leakage. Here you have to check
systematically:
Is there a saw at Q7? Is a Saw/ Rectangle at the Testpoint near C48.
If yes:
Are the Key-CV, Cutoff-CV present at the Filterchip?
Is the Gate present at the envelope?

In my Polysix a CD4066, which does the envelope and
Rectangle/Saw-Switching, was dead. But this is only one out of many
possible causes.

> KLM 369 : Octave, waveform, PW/PWM, PWM speed and sub osc pots and
> switchs doesn't affect the sound in anyway. Will check the whole card,
> connectors, traces etc
>

This is not KLM369, but the cause will be most likely the battery
leakage. The ICs 28 and 29 (which provide the data for these parameters)
are enabled by the CPU port P24. The corresponding trace runs under the
battery. (PWM speed won't work as long as the wavefrom select does not
work). -> So GOTO TOP: First do a restauration of the battery leakage.


Florian

Two typos / corrections....


Am 04.10.2016 um 14:23 schrieb Florian Anwander fanwander@mnet-online.de
[PolySix]:

>
> desolder all IC is a wide range around the battery,
>

this should read
"desolder all ICs in a wide area around the battery"

> You need a electronic desoldering station.
>

Of course it is an "electric desoldering station" (not an "electronic")

Sorry...

Hi Florian

Thanks for the explanations. I'll fix the klm367 before the others.

I'm currently de-soldering the ICs (with electronic desoldering pump).
I've read many things about cleaning the card after battery leaking. What would you use for that ?

Hello Bastien

Am 04.10.2016 um 16:26 schrieb gruelbastien@yahoo.fr [PolySix]:

>
> I'm currently de-soldering the ICs (with electronic desoldering pump).
> I've read many things about cleaning the card after battery leaking.
> What would you use for that ?
>

First I washed the card with clean natural water (comme Volvic). You may
lay it for 10 minutes or so in the water. After that bath shake the
water off and then dry the pcb with a hair dryer. Some people recommend
acid buffering liquids, but those would help only if the battery leakage
happened only a few days ago.

After the washing and drying procedure I use a fiber glass pencil to
scrape all the residues from the pcb and make the traces blank and
shining again. Doing so makes it much easier to search for breaks in the
traces.

Florian

Hi

I've worked on the polysix this weekend:

I fixed the battery leakage and cleaned the metal panel.

I cleaned the klm367 without vinegar or baking soda, just water.
I offered it a bath of mineral water from the Pyrenees: it's good for synthesizers :-), brushed it with a toothbrush and dryed it with hairdryer.
I changed IC30 and IC31, D5 diode, put a cr2032 and it works !

Florian: as you were saying, after fixing the klm367 the problem with vco knobs disappeared. Danke

The only problem remaining is the silent voice 3.

I'll check it as soon as possible

Bastien

Hi again

Florian, I have the saw at Q7 but I can't find the test point near C48, maybe it's because I have a klm366B (new production), I can't find any test point on the voice 3.

I'm not sure how to check key-CV et cutoff-cv but the gate signal is present at pin 6 of the 2056 chip when voice 3 is used.

Can you please tell me how can I check the key-Cv and cutoff-CV signals please ?

You should sell that water on eBay. Call it magic synth water. 'Cures all synth ailments'

Yes, in very little bottles but very expensive :-)

Hi

I still have the problem with the voice 3 which doesn't work.
As Florian said, I checked the saw at Q7: ok. After this, he talked about checking signal at testpoint near C48, I can't find this testpoint

Anyone could help me with this ?

Hello

You may check pin 8  of IC35 (CD4066) - it is electrically the same position.

Florian

On 17.10.16 18:07 , gruelbastien@yahoo.fr [PolySix] wrote:

 

Hi

I still have the problem with the voice 3 which doesn't work.
As Florian said, I checked the saw at Q7: ok. After this, he talked about checking signal at testpoint near C48, I can't find this testpoint

Anyone could help me with this ?

Hello

Thank you Florian. I've checked the signal at pin 8 and I have the saw. Key CV, Cut off CV and gate are present too.

Hello again,

may i ask what fault you found and how? it wasnt clear from your post and i have some similar issues to sort out... an account of what you found may help immensely...! thanks

Hi
So: voice 3 was silent but the internal red LED was on when I pressed a key.

1) Swapped the 2056 chip with another one from a working voice: no change;
2) Swapped the 2044 chip with another one from a working voice: no change;
3) Followed Florian ideas for checking signal at different pins with oscilloscope: signal was here
4) Checked the signal at TP1 Sig out: no signal.
5) On the schematic, just before the TP1 there's a chip and resistor array, checked the resistor array: no signal at the voice 3 pin.
6) Before the array is the voice 3 out on pin 1 of IC33 (4558 chip): signal was good !
7) Checked the continuity: obviously it was dead. It was just this ! (－‸ლ) I missed it when I checked the board ...

Hello Bastien

On 19.10.16 10:12 , gruelbastien@yahoo.fr [PolySix] wrote:

 

7) Checked the continuity: obviously it was dead. It was just this ! (－‸ლ) I missed it when I checked the board ...

Ah, that is interesting. I once had a broken trace in a P6 voiceboard too. I always thought that it was my fault, because I had replaced the related chip before. So it is good to know, that broken traces have to be taken in account always.

Florian

thanks for the tips

Florian - or anyone else:

i have a voice card with an outright bad voice but then another one that also goes dead only on  resonance based sounds... does anyone have any insight as to what might be going on there - or where i might look? Anyone know which chip handles resonance voicing.. or how the circuit for resonance works so that I might be able to better troubleshoot it...?

thanks much!

Hi Florian
Sorry, I missed your last message. I was so happy to put back my polysix in my studio that I didn't came back to the forum :-)
Don't konw if this broken trace is also due to the battery leaking as on the klm367 or just because of the age of the synth... But yes: always verify all traces (twice in my case !)