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Poly800 DCO 1 does not play the right notes

Poly800 DCO 1 does not play the right notes

2015-11-25 by bagaeta@...

Hello, I'm a new member here, general synth geek and collector. I recently took delivery of a Poly800 but when I tried it I noticed some strange behavior, with some notes out of tune. After a bit of fiddling I think this is happening only with DCO1: when in double mode with DCO1 level turned down to 0 the notes are in tune. 

With DCO1 it looks like the DCO is not responding to notes (from the keyboard or MIDI) in the right fashion. So for example if I play C D E F it sounds kind of like C D Eb E (or something to that effect)

Any idea what could be causing this and how to fix it?

Thank you!

Bruno

Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

2015-11-25 by Michael Hawkins

That is extremely odd behavior because both DCO1 and DCO2 operate from  the same master oscillator but DCO2 has an interval and detune arrangement (parameters 31 and 32) that will offset DCO2 from DCO1. Other than that, all of the mechanics of DCO1 and DCO2 are inside of the tone generator chip - the MSM5232.
So first of all, make sure that parameters 31 and 32 are both set to zero (0) and see if the behavior is still seen.
Have you uploaded the default patches using audio "tape" load? Because sometimes bad patch data from a dead backup battery can cause unexpected effects.

/Mike
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      From: "bagaeta@... [korgpolyex]" <korgpolyex@yahoogroups.com>
 To: korgpolyex@yahoogroups.com 
 Sent: Wednesday, November 25, 2015 5:35 AM
 Subject: [korgpolyex] Poly800 DCO 1 does not play the right notes
   
    Hello, I'm a new member here, general synth geek and collector. I recently took delivery of a Poly800 but when I tried it I noticed some strange behavior, with some notes out of tune. After a bit of fiddling I think this is happening only with DCO1: when in double mode with DCO1 level turned down to 0 the notes are in tune. 

With DCO1 it looks like the DCO is not responding to notes (from the keyboard or MIDI) in the right fashion. So for example if I play C D E F it sounds kind of like C D Eb E (or something to that effect)

Any idea what could be causing this and how to fix it?

Thank you!

Bruno  #yiv3371858456 #yiv3371858456 -- #yiv3371858456ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv3371858456 #yiv3371858456ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv3371858456 #yiv3371858456ygrp-mkp #yiv3371858456hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv3371858456 #yiv3371858456ygrp-mkp #yiv3371858456ads {margin-bottom:10px;}#yiv3371858456 #yiv3371858456ygrp-mkp .yiv3371858456ad {padding:0 0;}#yiv3371858456 #yiv3371858456ygrp-mkp .yiv3371858456ad p {margin:0;}#yiv3371858456 #yiv3371858456ygrp-mkp .yiv3371858456ad a {color:#0000ff;text-decoration:none;}#yiv3371858456 #yiv3371858456ygrp-sponsor #yiv3371858456ygrp-lc {font-family:Arial;}#yiv3371858456 #yiv3371858456ygrp-sponsor #yiv3371858456ygrp-lc #yiv3371858456hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv3371858456 #yiv3371858456ygrp-sponsor #yiv3371858456ygrp-lc .yiv3371858456ad {margin-bottom:10px;padding:0 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Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

2015-11-26 by bagaeta@...

Thank you Mike. I changed the batteries, uploaded the factory presets in the unit, turned the detune off and tested the unit with a tuner, varying the levels of DCOs 1 and 2.

It turns out the problem is DCO2 which is slightly flat (around -10 cents) and whose pitch fluctuates a bit (-10 to -20 cents). With a very sensitive tuner it can be seen that the DCO2 pitch is quite unstable when that of DCO1 is nice and steady. This happens with detune off, and all modulation turned off. This is enough to make the unit sound weird with double patches, and with single patches, the weird "scale" is the result of different notes being allocated between the two DCOs which are slightly out of tune with each other.

I don't know much about electronics but after downloading the service manual and peering at the schematics it looks like the problem may be somewhere in the detune circuit (22) which affects CLK2 even when detune is off. With detune on the difference between the two DCOs gets worse, never better.

Do you know whether that can be fixed easily without changing the main board?

Thank you

Bruno


Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

2015-11-26 by Michael Hawkins

Yes, this can be definitely be fixed with swapping out the main board. But, the detune circuit uses IC17, IC18, IC19 and IC20.
I would definitely be checking the power supply and making sure that the +5 rail is close to exactly +5 volts and that it is smooth. You need electronics skills or someone that has them, at this point.
/Mike
Show quoted textHide quoted text
      From: "bagaeta@... [korgpolyex]" <korgpolyex@yahoogroups.com>
 To: korgpolyex@yahoogroups.com 
 Sent: Thursday, November 26, 2015 4:41 AM
 Subject: Re: [korgpolyex] Poly800 DCO 1 does not play the right notes
   
    Thank you Mike. I changed the batteries, uploaded the factory presets in the unit, turned the detune off and tested the unit with a tuner, varying the levels of DCOs 1 and 2.
It turns out the problem is DCO2 which is slightly flat (around -10 cents) and whose pitch fluctuates a bit (-10 to -20 cents). With a very sensitive tuner it can be seen that the DCO2 pitch is quite unstable when that of DCO1 is nice and steady. This happens with detune off, and all modulation turned off.  This is enough to make the unit sound weird with double patches, and with single patches, the weird "scale" is the result of different notes being allocated between the two DCOs which are slightly out of tune with each other.
I don't know much about electronics but after downloading the service manual and peering at the schematics it looks like the problem may be somewhere in the detune circuit (22) which affects CLK2 even when detune is off. With detune on the difference between the two DCOs gets worse, never better. 
Do you know whether that can be fixed easily without changing the main board?
Thank you
Bruno

Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

2015-11-27 by bagaeta@...

Thank you! I'm not sure my multimeter is accurate enough to measure the voltage that precisely. But in a fit of desperation I attacked the board with a Q-tip and contact cleaner and sure enough rubbing the bottom right pins of IC18 (right under the coin battery) and R65 fixes the problem, at least temporarily. I'll see how it goes before seeking a more permanent fix (fingers crossed).

BTW the coin battery is not shown on the diagrams in the service manual. Is this because I have a newer board revision? My main board version is KLM-596-8

Bruno


Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

2015-11-27 by <backshall1@...>

Yes, version 8 has a lithium coin cell soldered in. I don’t think I’ve ever seen a schematic with this revision. I’ve seen KLM-596-2,6,7 and 8 boards and the only schematic I’ve seen was for version 2, with no battery and no solder tabs where the battery would eventually be added. Versions 6 an 7 had the solder tabs but no battery, and R1 and D1 had to be removed from the board when adding a battery. Version 8 had no R1 or D1 on the board. This resistor and zener diode used to be over near the 9V input.
Don B.
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From: mailto:korgpolyex@yahoogroups.com 
Sent: Thursday, November 26, 2015 8:18 PM
To: korgpolyex@yahoogroups.com 
Subject: Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

  
Thank you! I'm not sure my multimeter is accurate enough to measure the voltage that precisely. But in a fit of desperation I attacked the board with a Q-tip and contact cleaner and sure enough rubbing the bottom right pins of IC18 (right under the coin battery) and R65 fixes the problem, at least temporarily. I'll see how it goes before seeking a more permanent fix (fingers crossed). 


BTW the coin battery is not shown on the diagrams in the service manual. Is this because I have a newer board revision? My main board version is KLM-596-8


Bruno

Re: [korgpolyex] Poly800 DCO 1 does not play the right notes

2015-11-27 by Michael Hawkins

If your patches are still intact after you power off and you have no C cells in the synth, then the battery is good.
If you lose your patches after you power off and back on and you have no C cells in the poly, then the battery needs to be replaced.

/Mike
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      From: "bagaeta@... [korgpolyex]" <korgpolyex@yahoogroups.com>
 To: korgpolyex@yahoogroups.com 
 Sent: Thursday, November 26, 2015 10:57 PM
 Subject: Re: [korgpolyex] Poly800 DCO 1 does not play the right notes
   
    Thank you. Is there any value in replacing that battery with a fresh one? It must be dead by now...
Bruno  #yiv4013564334 #yiv4013564334 -- #yiv4013564334ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv4013564334 #yiv4013564334ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv4013564334 #yiv4013564334ygrp-mkp #yiv4013564334hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv4013564334 #yiv4013564334ygrp-mkp #yiv4013564334ads {margin-bottom:10px;}#yiv4013564334 #yiv4013564334ygrp-mkp .yiv4013564334ad {padding:0 0;}#yiv4013564334 #yiv4013564334ygrp-mkp .yiv4013564334ad p {margin:0;}#yiv4013564334 #yiv4013564334ygrp-mkp .yiv4013564334ad a {color:#0000ff;text-decoration:none;}#yiv4013564334 #yiv4013564334ygrp-sponsor #yiv4013564334ygrp-lc {font-family:Arial;}#yiv4013564334 #yiv4013564334ygrp-sponsor #yiv4013564334ygrp-lc #yiv4013564334hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv4013564334 #yiv4013564334ygrp-sponsor #yiv4013564334ygrp-lc .yiv4013564334ad {margin-bottom:10px;padding:0 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