Discussion about the Korg PolySix synthesizer

Hi everyone!

Just got into the exciting world of PolySix yesterday, when I was
given two p6's for free!

One is in great shape, though suffered some battery damage. the other
is a near write-off with sever corrosion on several areas of the main
boards.

After repairing all bad traces and vias (AFAIK) on the good p6, and
replacing the IC31 SN74LS08 with a SN7408 (note the lack of LS),
things seem to only half-work.

The sub-osc doesn't appear to work, the ADSR only sort of works
sometimes, the effects don't work, but there is a slow delay that is
constantly applied to the signal.

The programmer does not function at all. Sometimes program lights 2
and 5 will be on, other times just 3. Pressing any of the buttons on
the programmer has no effect.

I'm wondering if I really should replace the IC31 7408 with a 74LS08.
The difference being that the LS has zener diodes, and different
(higher?) impedance.

Any suggestions on where to look next?

Also, I believe the delay chips will need to be recallibrated. Are the
trimmers on the bottom of each BBD section the bias or offset
controls? OR neither?

Thanks in advance!

Sean

I would replace both those 7408s in that area.  the chips I used are
nte7408.  dont under etimate the power of the dark side (aka bad
traces) I scratched all the traces (on the top of the board) away from
the 2 7408s.  You may want to replace the in line 10k? resistor
network to.  the acid can get to that.

--- In PolySix@yahoogroups.com, "essboyer" <sean@...> wrote:

>
> Hi everyone!
> 
> Just got into the exciting world of PolySix yesterday, when I was
> given two p6's for free!
> 
> One is in great shape, though suffered some battery damage. the other
> is a near write-off with sever corrosion on several areas of the main
> boards.
> 
> After repairing all bad traces and vias (AFAIK) on the good p6, and
> replacing the IC31 SN74LS08 with a SN7408 (note the lack of LS),
> things seem to only half-work.
> 
> The sub-osc doesn't appear to work, the ADSR only sort of works
> sometimes, the effects don't work, but there is a slow delay that is
> constantly applied to the signal.
> 
> The programmer does not function at all. Sometimes program lights 2
> and 5 will be on, other times just 3. Pressing any of the buttons on
> the programmer has no effect.
> 
> I'm wondering if I really should replace the IC31 7408 with a 74LS08.
> The difference being that the LS has zener diodes, and different
> (higher?) impedance.
> 
> Any suggestions on where to look next?
> 
> Also, I believe the delay chips will need to be recallibrated. Are the
> trimmers on the bottom of each BBD section the bias or offset
> controls? OR neither?
> 
> Thanks in advance!
> 
> Sean
>

Hey thanks a lot synthmdl76.

That's not a bad idea. So using a 7408 as opposed to the 74LS08 is
fine?  I didn't think they should be too different.

The other area I think is causing the problems, is in the programmer.
Which are the logic chips that control that? Or is it the 7408 gates?

I have a feeling that all my problems relate to the programmer being
out of whack.

Thanks again for your help!

Cheers,
Sean

Well, after a bit more troubleshooting, I discovered another bad trace
from the processor to somewhere. Once I repaired that, the programmer
started working *almost* properly. The Bank B and Program 2 lights
ALWAYS stay on, but I can select the other banks and programs no
problem now. Some of the programs appear to be blank or possibly not
working, but at least I'm getting somewhere!

My next big issue seems to be that the sub oscillator, and octave
selector switch don't seem to work. Sometimes the waveform selector
will work, and other times not. All the traces seem to be good on the
control board... I've cleaned the switches with contact cleaner, and
still nothing. 

Are these controls related to the corrosion-damage-zone?

I have not yet replaced the topmost 7408 nor the resistor array, as
they seem to be okay. Maybe I will do the 7408 just to be sure.

Hi.

Check my last P6 repair post. Both Bank B, preset 2 and preset 6 leds
are going to IC30's leg number 6.

Replace IC30 and clean any corrosion which may be found underneath.

I would also use the original 74LS08 (74HC08 seems to works too).

;)







--- In PolySix@yahoogroups.com, "essboyer" <sean@...> wrote:

>
> Well, after a bit more troubleshooting, I discovered another bad trace
> from the processor to somewhere. Once I repaired that, the programmer
> started working *almost* properly. The Bank B and Program 2 lights
> ALWAYS stay on, but I can select the other banks and programs no
> problem now. Some of the programs appear to be blank or possibly not
> working, but at least I'm getting somewhere!
> 
> My next big issue seems to be that the sub oscillator, and octave
> selector switch don't seem to work. Sometimes the waveform selector
> will work, and other times not. All the traces seem to be good on the
> control board... I've cleaned the switches with contact cleaner, and
> still nothing. 
> 
> Are these controls related to the corrosion-damage-zone?
> 
> I have not yet replaced the topmost 7408 nor the resistor array, as
> they seem to be okay. Maybe I will do the 7408 just to be sure.
>

Thanks for the suggestions once again!

I've replaced IC 30 and 31 with 7408, but will buy some 74LS08 and try
those.

Meanwhile, I'm down to my last few problems:

*Sub OSC does not work at all (aka is always off)

*Octacve 16' and 4' are both the same. (which is actually 16')

*Cannot write to memory. The LEDs look like things are going okay, but
then when you try to recall the last saved program, it is blank.

*Bank 2 and Program 2 LED's are always on still

*When you call a program, they are either blank, or the same one patch

I suspect that the 7408's might need replacing again, but that there
is something going on with IC29, or somewhere else along the chain
that included the subosc and octave.

PS - I got an original paper service and users manual in great
condition. I will make PDF copies of both and post link when they are
online, if that is not in violation of a rule here.

Cheers,
Sean

I have the PDF manuals that I got from Korg hosted online.  If you
can make better PDFs than those, by all means do it!  :)

I don't think anybody would complain about that.

On Dec 29, 2007 1:22 PM, essboyer <sean@boyercentral.net> wrote:
> Thanks for the suggestions once again!
>
> I've replaced IC 30 and 31 with 7408, but will buy some 74LS08 and try
> those.
>
> Meanwhile, I'm down to my last few problems:
>
> *Sub OSC does not work at all (aka is always off)
>
> *Octacve 16' and 4' are both the same. (which is actually 16')
>
> *Cannot write to memory. The LEDs look like things are going okay, but
> then when you try to recall the last saved program, it is blank.
>
> *Bank 2 and Program 2 LED's are always on still
>
> *When you call a program, they are either blank, or the same one patch
>
> I suspect that the 7408's might need replacing again, but that there
> is something going on with IC29, or somewhere else along the chain
> that included the subosc and octave.
>
> PS - I got an original paper service and users manual in great
> condition. I will make PDF copies of both and post link when they are
> online, if that is not in violation of a rule here.
>
> Cheers,
> Sean
>
>
>
>
>
>
>
> PolySix "Digiest" Page: http://www.acc.umu.se/~amber/Poly6
> Yahoo! Groups Links
>
>
>
>



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