Author Topic: Korg Poly 61 Pitch Bend Issue  (Read 401 times)

Offline theseacowexists

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Korg Poly 61 Pitch Bend Issue
« on: April 15, 2020, 05:40:13 PM »
Anyone got a Korg Poly 61? We got one a few months ago, and everything works fine except the pitch bend up - it doesn't change the pitch at all. Pitch bend down works and so do the DCO and VCF bends (which are on the Y axis of the joystick. The joystick pots have been cleaned and are connected to the board. We read somewhere on another forum that adjusting the bend up adjustment pot on the board could fix this, but it doesn't work on this one. In fact that trimpot seemed to be busted. Swapped it out for a different one we had laying around of a different value, no luck either.

Offline bujbot

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Re: Korg Poly 61 Pitch Bend Issue
« Reply #1 on: April 16, 2020, 06:14:54 PM »
Anyone got a Korg Poly 61? We got one a few months ago, and everything works fine except the pitch bend up - it doesn't change the pitch at all. Pitch bend down works and so do the DCO and VCF bends (which are on the Y axis of the joystick. The joystick pots have been cleaned and are connected to the board. We read somewhere on another forum that adjusting the bend up adjustment pot on the board could fix this, but it doesn't work on this one. In fact that trimpot seemed to be busted. Swapped it out for a different one we had laying around of a different value, no luck either.

Hey.  I have a Poly-61 that I've repaired in the past.  When you say the joystick pots are cleaned, which ones are you referring to?  The second pot to the left on the main panel is the pitch bend depth (Korg calls this a Joystick Pot too).  Most obvious question, is that fully counter-clockwise?  I would check that that pot is functioning as expected.  Second there is a pot in the joystick itself, it also needs to be checked that it is functioning (I think I have a spare one if it is not).

Really be careful when adjusting pots on the board, you can throw it out of wack pretty quick, mine is very sensitive  :o

BTW, if you have it open what state is the battery in?  That can go at any time!  Swap it out if it is still original.

Good luck!
« Last Edit: April 16, 2020, 08:30:03 PM by bujbot »

Offline theseacowexists

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Re: Korg Poly 61 Pitch Bend Issue
« Reply #2 on: April 17, 2020, 09:27:48 AM »
So the pots that are inside the joystick assembly (there are two for each axis) are the ones we've cleaned. The pitchbend depth pot on the front panel works, and it varies the depth of the pitchbend down. Up does nothing. The bend up adjustment trimpot that I tried adjusting (and replacing) on one of the circuit boards under the hood. There's also a bend down adjustment trimpot, but since that is functioning as it should, I left it alone.

The other reason we had it open, in fact, was to replace the battery. It had corroded pretty bad, but it doesn't appear to have done any damage. So we swapped it out for a battery holder and life is good! Except for no upwards pitch bend, of course.

Offline bujbot

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Re: Korg Poly 61 Pitch Bend Issue
« Reply #3 on: April 17, 2020, 10:16:22 AM »
So the pots that are inside the joystick assembly (there are two for each axis) are the ones we've cleaned. The pitchbend depth pot on the front panel works, and it varies the depth of the pitchbend down. Up does nothing. The bend up adjustment trimpot that I tried adjusting (and replacing) on one of the circuit boards under the hood. There's also a bend down adjustment trimpot, but since that is functioning as it should, I left it alone.

The other reason we had it open, in fact, was to replace the battery. It had corroded pretty bad, but it doesn't appear to have done any damage. So we swapped it out for a battery holder and life is good! Except for no upwards pitch bend, of course.

Ok cool, another area these fail are the wire jumpers to the board themselves.  They can start to corrode a bit or lose friction.  What I would do to check was to remove the connector and take a pin (like the leg of a resistor) and stick it in each plug to make sure I could feel the resistance.  If I couldn't, I would fix/replace.

Other than cleaning are you checking voltages around the suspect pot to make sure it's doing anything?  Probably want to start tracing the voltage from the pot all the way to the board and beyond.  Oscilloscopes help here but a multi-meter could work.