Korg Poly 800 problem joystick DCO e VCF not working

[veraferro]

hello everyone,
I ask for your help in solving a problem on my Korg Poly 800 ..
after changing the cutoff, resonance and noise the joystick does not work properly ..
essentially modulation DCO and VCF (above and below) is mute not working but if I move the joystick to the right and left respectively have pitch bend + DCO (moving right) pitch bend + VCF (moving left).
also changing 12/24 db malfunctioning; 24 db works fine but if I move about 12 db sound is muted or sometimes very low.

you think what could have happened?

[meatballfulton]

I ask for your help in solving a problem on my Korg Poly 800 ..
after changing the cutoff, resonance and noise the joystick does not work properly ..

Changing the patch parameters or a physical modification?

also changing 12/24 db malfunctioning; 24 db works fine but if I move about 12 db sound is muted or sometimes very low.

What is this, a modification? Poly 800 does not let you select the filter slope.

[veraferro]

Changing the patch parameters or a physical modification?

What is this, a modification? Poly 800 does not let you select the filter slope.

meatballfulton, thanks for your response ..
I made physical change by installing 3 potentiometers for control cuttoff, resonance and noise ..

I also installed a switch to convert 24 db 12 db on the integrated 2069.

[meatballfulton]

Do you have the schematics? I would look there first. Good luck.

[veraferro]

Do you have the schematics? I would look there first. Good luck.

on the internet I found this: http://manuals.fdiskc.com/flat/Korg%20P ... matics.pdf

[Weirdofromouterspace]

Hi,

changing the cutoff, resonance and noise [...] also changing 12/24 db

I installed exactly the same modifications on mine during the last 2 weekends. However, I haven't tested them yet since I am waiting for a rotary data entry knob which is currently in the mail on its way from Austria to me.

Anyway...

the joystick does not work properly ..
essentially modulation DCO and VCF (above and below) is mute not working

Check whether dirt has gotten on the corresponding conductor path of the pot, and whether the cable connectors are really firmly attached, especially if it worked fine before.
The pitchbend didn't work too well in mine; I cleaned the conductor path with rubbing alcohol (isopropanol), hope it gets better. These pots seem impossible to source, they have a divided conductor path.

also changing 12/24 db malfunctioning; 24 db works fine but if I move about 12 db sound is muted or sometimes very low. you think what could have happened?

Check for bad solder joints. This behavior would be typical for one. Also, check whether there are poorly isolated wire ends that could occasionally get in contact and thus short-circuit something.
Did you solder the wires directly to the IC? I did not: I connected them to the existing solder joints underneath the PCB. I will add a picture tonight (German time, that is )

Changing the patch parameters or a physical modification?

These are physical modifications often named 'moog slayer' (cutoff and resonance) and 'FM800' (noise)
http://synthmod.net/korg/moog_slayer/
http://synthmod.net/korg/fm800/
http://www.strellis.com/poly800.shtml

What is this, a modification? Poly 800 does not let you select the filter slope.

The filter IC provides both 12 and 24 dB/oct. It has a 24 dB/oct outlet (pin 6), which is connected to an electrolytic capacitor (C103 in the schematics) by default. It also has a 12 dB/oct outlet (pin 5), which is unconnected. This is also displayed in the corresponding block schematic of the IC, which is in the service manual.

Looks like this:
<Argh, how do I upload pics? Well, here's at least a link - 2nd post in the thread>

https://www.muffwiggler.com/forum/viewt ... ?p=1656530

The mod works as follows:
Desolder the above mentioned capacitor and solder it to a simple toggle switch (center connector). Connect its other end to its original (+) position with some wire (make sure the polarity is correct). Solder one wire each to the pin 5 and pin 6 connectors, and their other ends to the remaining connectors of the switch. That's it.

[veraferro]

hello Weirdofromouterspace,
thank you very much for your help, the change was made in August 2014 and everything worked perfectly ..
I connected the poly 800 via MIDI to the PC and it was ok ..
Now the joystick malfunction, modulation DCO is combined with the pitch bend to the left and the modulation VCF combines with the pitch bend to the right.
In short, the DCO and VCF is present but not up and down but by moving the joystick left and right ..
I thought it was due to a problem of IC6 (14053) I replaced it with an integrated recovered by another poly 800 functioning of a friend of mine but I have not solved the problem ..
I also replaced the entire board KLM-599 always recovered from another poly 800 but the problem is always there, so I think the solution lies on the main board ..

for the problem of the filter 24/12 db I follow your advice and I check the welds;
welds I made under the PCB.

[Weirdofromouterspace]

Hi veraferro,

Now the joystick malfunction, modulation DCO is combined with the pitch bend to the left and the modulation VCF combines with the pitch bend to the right.
In short, the DCO and VCF is present but not up and down but by moving the joystick left and right ..

when you say "is combined..." - do you mean moving the joystick triggers both pitchbend and DCO/VCF simultaneously, or does it trigger DCO/VCF instead of pitchbend?

I think the solution lies on the main board ..

I think a good starting point is having a very close look at the cable connectors that link the KLM599. Perhaps it doesn't sit firmly in its place, or a cable is damaged, or a solder joint is broken, or something (dirt, a little piece of metal foil or wire, whatever...) interferes with the connector points?

Weird, anyway...

[veraferro]

Hi veraferro,

when you say "is combined..." - do you mean moving the joystick triggers both pitchbend and DCO/VCF simultaneously, or does it trigger DCO/VCF instead of pitchbend?

hello Weirdofromouterspace,
the joystick is active pitchbend and DCO / VCF simultaneously, exactly!
wire connections are correct and isolated.

do you think the board KLM-601 welded on the mainboard of J4, J5, J6, could be the cause if it works badly?

[Weirdofromouterspace]

Hi veraferro,

the joystick is active pitchbend and DCO / VCF simultaneously, exactly!?

OK. That means one pot somehow has contact to both DCO/VCF and pitchbend subcircuits .

So the big question seems to be "where is that connection that should not be?".

do you think the board KLM-601 welded on the mainboard of J4, J5, J6, could be the cause if it works badly

I have no idea . Perhaps someone who has an oscilloscope and knows how to use it may help?

[Weirdofromouterspace]

Hi,

here's the pictures I said I'd post:

This shows how I connected the wires for the 12/24 dB/oct switch (green = 12 dB/oct; red = 24 dB/oct):



This is where the (+) wire is connected to where C103 used to be:



And these two show the switch with the attached wires and capacitor:





Hope that helps a bit. There are good pictures for the Moogslayer and FM800 mods available on the net (check out the URLs I posted above), but I didn't find any for the 12/24 dB/oct mod. May these be useful for other modders & circuit benders .

[veraferro]

hello,
thanks for the help,
I have altered in a way and maybe that's why it does not work ..
following the pattern of work:




tonight I try to change the connections as your edit ..

[veraferro]

hello Weirdofromouterspace,
I'm sorry to bother you again, but I noticed in the second picture that you have also installed two resistors, right?
of what value are they?

[Weirdofromouterspace]

Hi veraferro,

I have altered in a way and maybe that's why it does not work ..

erm... you might try to install the capacitor with correct polarity .

but I noticed in the second picture that you have also installed two resistors, right?

No, I didn't add any resistors. Do you mean the ones on top of R18 and R20? They were there when I got the synth...

Possibly the previous owner did this to lower the resistor value according to 1/R(total) = 1/R(1) + 1/R(2)...

It can, if at all, only be a minor change, imho.

[veraferro]

Hi veraferro,

erm... you might try to install the capacitor with correct polarity .

Now I try to change it as your own, let you know ..