Synth-DIY Yahoo! Groups Archives

Mono/Poly Tuning Problems - OSC4

2015-09-14 by voltagegrove@yahoo.com

Hey Guys,

So its a bit of a long story to give you all the details but here is the abridged version. I went to install the MidiPoly kit and there were many issues right off the bat. When troubleshooting I had accidentally shorted the + and - 5v coming from the pitch and mod wheels. It blew the two fuses that sit on the back board. One replacing the fuses, all Oscillator were drastically out of tune and seemed to be out of phase as well (not all triggering together regardless of any control tests). After this had happened I decided to take it to a tech to get checked out. So far so good, Midi, pitch/mod wheels and tuning are all on point. EXCEPT for oscillator 4. For some reason he has not been able to get OSC4 up to par with the other 3. He seems to know what he is doing, but the workload in diagnosing the origin of the problem is racking up hours. I was hoping that someone could guide us in the proper direction. I would really greatly appreciate it any and all help. Thanks

Jarrett

Re: Mono/Poly Tuning Problems - OSC4

2015-09-14 by voltagegrove@yahoo.com

And by what I meant by out of phase was seemingly a beating that was occurring between all OSC's. Detuning them on front panel would only get them close but they were still warbling slightly which was never the case before.

Re: [korg_mono-poly] Mono/Poly Tuning Problems - OSC4

2015-09-14 by <kimouts@gmail.com>

Maybe you could contact Ko from modeless factory. He is ace in servicing them ;-)

On Sep 14, 2015 6:27 AM, "voltagegrove@yahoo.com [korg_mono-poly]" <korg_mono-poly@yahoogroups.com> wrote:

Hey Guys,

So its a bit of a long story to give you all the details but here is the abridged version. I went to install the MidiPoly kit and there were many issues right off the bat. When troubleshooting I had accidentally shorted the + and - 5v coming from the pitch and mod wheels. It blew the two fuses that sit on the back board. One replacing the fuses, all Oscillator were drastically out of tune and seemed to be out of phase as well (not all triggering together regardless of any control tests). After this had happened I decided to take it to a tech to get checked out. So far so good, Midi, pitch/mod wheels and tuning are all on point. EXCEPT for oscillator 4. For some reason he has not been able to get OSC4 up to par with the other 3. He seems to know what he is doing, but the workload in diagnosing the origin of the problem is racking up hours. I was hoping that someone could guide us in the proper direction. I would really greatly appreciate it any and all help. Thanks

Jarrett

Re: [korg_mono-poly] Mono/Poly Tuning Problems - OSC4

2015-09-14 by Anwander, Florian

Hello Jarrett

Did your tech realign the powersupply and the Key-Assigner (=D/A
converter)? This has to be done first. The order is important. See
http://fa.utfs.org/diy/korg_monopoly/mp_20_adjustment_1.gif

Also it is important how the Detune-knob and the individual Tune-knobs
are set while the tuning procedure. The official adjustment description
for the VCOs does not mention this clearly. I recommend my procedure:
http://fa.utfs.org/diy/korg_monopoly/vco_adjustment.html

Regards
Florian

RE: [korg_mono-poly] Mono/Poly Tuning Problems - OSC4

2015-09-14 by <alanmdicker@yahoo.co.uk>

If the voices are changing in pitch even after a warm up period then maybe also check the integrity of KLM 357 the heat compensation board. This can have a massive effect on the VCO pitches. Also does hard sync still work on voice 4?

Sent from Mail for Windows 10

From: voltagegrove@yahoo.com [korg_mono-poly]
Sent: 14 September 2015 04:27
To: korg_mono-poly@yahoogroups.com
Subject: [korg_mono-poly] Mono/Poly Tuning Problems - OSC4

Hey Guys,

So its a bit of a long story to give you all the details but here is the abridged version. I went to install the MidiPoly kit and there were many issues right off the bat. When troubleshooting I had accidentally shorted the + and - 5v coming from the pitch and mod wheels. It blew the two fuses that sit on the back board. One replacing the fuses, all Oscillator were drastically out of tune and seemed to be out of phase as well (not all triggering together regardless of any control tests). After this had happened I decided to take it to a tech to get checked out. So far so good, Midi, pitch/mod wheels and tuning are all on point. EXCEPT for oscillator 4. For some reason he has not been able to get OSC4 up to par with the other 3. He seems to know what he is doing, but the workload in diagnosing the origin of the problem is racking up hours. I was hoping that someone could guide us in the proper direction. I would really greatly appreciate it any and all help. Thanks

Jarrett

Re: Mono/Poly Tuning Problems - OSC4

2015-09-14 by voltagegrove@yahoo.com

So I spoke to him briefly this morning. He of course knew of all the nuggets that you guys had sent. Apparently it is beyond basic calibration, he doesn't say its out of tune (which it is), but that its unstable. Not quite sure of the exact differences are. He also said that his next step was to venture into the boards fastened to the top panel.

Is there anyway it could be a bad cap? I am assuming its not an IC because full functionality is there...

What would be the problem if OSC4 didn't sync?

Re: Mono/Poly Tuning Problems - OSC4

2015-09-15 by voltagegrove@yahoo.com

Is there any chance that it could be one of the SSM2033 chips? The Oscillator functions beautifully minus the whole being unstable and drastically out of tune. There are some up for sale on ebay. Not sure if I should pull the trigger on those... Any ideas with the latest info I posted earlier?

Re: [korg_mono-poly] Re: Mono/Poly Tuning Problems - OSC4

2015-09-15 by Florian Anwander

Hello,

to be honest. I think it does not make sense to talk about it, if we do not have a reliable technical description of the real facts. I don't want to sound unpolite, but though you have some technical knowledge, everything you are writing is a second hand information.

You technician should write here. We even do not know whether the VCO in question is flat, or sharp. He could provide detailed data of the control voltages at the four VCOs.

And before he replaces the 2033, he should swap VCO-chips first between the voices (that is the usual procedure in such a case - even if it is a bit cumbersome due to the thermistor on the 2033).

Florian

15.09.15 04:37 , voltagegrove@yahoo.com [korg_mono-poly] wrote:

Is there any chance that it could be one of the SSM2033 chips? The Oscillator functions beautifully minus the whole being unstable and drastically out of tune. There are some up for sale on ebay. Not sure if I should pull the trigger on those... Any ideas with the latest info I posted earlier?