Synth-DIY Yahoo! Groups Archives

Joystick problems

2015-07-10 by kogz23@...

Hi all,
So I am having problems with the joystick, mainly the pitch bend.
When used pitching up cuts the sound out. Moving it slowly up the pitch goes up, then down then cuts out. When moving the bender down the pitch goes down, but way way down so the sound is barley audible.
Pin 7 of IC 10 is giving 1.986V with the bend in the centre, 0.012V all the way down, 3.99V all the way up.
Pin 2 of the bend pot gives roughly 2V centre, 4V all the way down and 0V all the way up. This is the opposite of what I would expect.
Other readings that I thought might be relevent: Pin 7 of IC38, which I assume is the output the service manual refers to, is 3V where the manual says it should be 4V.
Also pin 7 of IC35 is 0.8V bend centre, 2.5V bender down, -3.5V bender up. Again, is this correct?
Thanks as ever!
Al

Re: [korgpolyex] Joystick problems

2015-07-10 by Michael Hawkins

Check out the joystick operation PDF in the files section. It explains the operation of the circuit quite well. Maybe that will help.

/Mike

From: "kogz23@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Friday, July 10, 2015 2:00 AM
Subject: [korgpolyex] Joystick problems

Hi all,
So I am having problems with the joystick, mainly the pitch bend.
When used pitching up cuts the sound out. Moving it slowly up the pitch goes up, then down then cuts out. When moving the bender down the pitch goes down, but way way down so the sound is barley audible.
Pin 7 of IC 10 is giving 1.986V with the bend in the centre, 0.012V all the way down, 3.99V all the way up.
Pin 2 of the bend pot gives roughly 2V centre, 4V all the way down and 0V all the way up. This is the opposite of what I would expect.
Other readings that I thought might be relevent: Pin 7 of IC38, which I assume is the output the service manual refers to, is 3V where the manual says it should be 4V.
Also pin 7 of IC35 is 0.8V bend centre, 2.5V bender down, -3.5V bender up. Again, is this correct?
Thanks as ever!
Al

Re: [korgpolyex] Joystick problems

2015-07-10 by kogz23@...

Yes, I read it. That is why I was not sure about getting 4V with the bender down and 0v all the way up,
Cheers
Al

Re: [korgpolyex] Joystick problems

2015-07-11 by Michael Hawkins

You need to sort out the joystick behavior first before trying to tune the master.

The tone generator is set up as two blocks of four voices each. And since you say that the first four notes hit have low tones, I would say that there is a problem with the DCO1 harmonics selection section. There's a bunch of opamps. Check the output pins of the MSM5232 while sounding notes. Then work your way through each of the opamps. Switch the waveform selection from square to sawtooth and see if one is OK and one is not. That will help to narrow down the problem.

/Mike

From: "kogz23@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Friday, July 10, 2015 2:17 PM
Subject: Re: [korgpolyex] Joystick problems

Now I am just trying to get the thing in tune, will troubleshoot the joystick later.
Following the service manual master oscillator procedure I can not get as high as -1oct C. The highest I can get is -1oct B. As well as this there is a problem with a massive drop of pitch (several octaves so it sounds like a crackle) for the first 4 keys hit. The next 4 sound fine, then the pattern starts again. It is not specific to any key, just the order in which they are hit. Hitting the same key twice doesn't effect the counting. I hope this makes sense!
I'm getting the correct +/-5V. Any ideas where to look? I wanna get this baby back to full life!
Thanks
Al

Re: [korgpolyex] Joystick problems

2015-07-12 by kogz23@...

Well by hook or crook it looks like the Poly is now fixed. Famous last words, I know, I've probably cursed it now!
I tracked the problem down to being IC17 (mainly through luck). It is a 40H074 and looks like it is part of the master oscillator. It fixed the tuning problems and the issues with the joystick.
Thanks for all the input on this one and putting up with my often stupid questions. I must admit, after repairing a few synths I have found the Poly 800 to be quite a tricky one.
Cheers
Al