Yamaha CS-50 calibration frustration (KAS board) Solved!

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Yamaha CS-50 calibration frustration (KAS board) Solved!

Postby Yekuku » Thu Jun 26, 2014 11:05 pm

this really gives me a headache, I would appreciate some help if possible.
I am experiencing irregular note tracking with a repeating pattern over the octaves and some mild distortion on some voices.
I am stuck on calibrating the KAS board.
What I have done so far:
-I am studying the cs-50/60/80 service manuals and cs servicing guide for months ! :)
-PSU calibrated
-I have replaced all CMOS on the KAS board.
1) adjusted master tuning TU=4.0V ->VR11 Sub Board
2) adjusted Octave ladder network to 250mv ->VR1 Kas board. Checked all the network resistors and they are within specs.
3) Tried to adjust the voltage follower LM310H..... FAILED!
By reading the manuals , I understand that I should adjust VR3 so that pin 6 of the LM310H =125mV while pressing the C1. I am doing this and I am getting 2.11 V. I thought that the lm310H was shot so I replaced it with a LM310N but i still have the same problem.
Can anybody please explain the function of the voltage follower ?
any ideas on how to calibrate it?
Many thanks
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Last edited by Yekuku on Sun Sep 14, 2014 12:27 pm, edited 2 times in total.
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Re: Yamaha CS-50 calibration frustration (KAS board)

Postby hernanbaldi » Fri Jul 18, 2014 6:55 pm

Adjust as follows:

TU=4.000V
IC2 Pin13 = 250.0mV
IC3 pin6 = 2125mV

Check K1 to K4 from 250.0mv (Low C) and 4000mV (Hi C).

Good luck !
Ing. Hernán Baldi
www.sintetizadores.com.ar
Info@sintetizadores.com.ar
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Re: Yamaha CS-50 calibration frustration (KAS board)

Postby Yekuku » Sat Jul 19, 2014 11:20 am

hernanbaldi wrote:IC3 pin6 = 2125mV

:o
I have gone through the whole cs-50/60/80 service manuals and cs servicing guide, and I have seen no mention about this. where exactly is it mentioned ?
Many thanks hernanbaldi, your information was priceless.
I ll check it out and I ll keep you informed about how it goes.
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Re: Yamaha CS-50 calibration frustration (KAS board)

Postby Yekuku » Sun Jul 20, 2014 12:15 pm

Unfortunately it did not go very well...
I have adjusted the KAS board up to specs and I am still having scrambled notes with repeating pattern over the octaves. Some notes are duplicates.
Since I have checked the keyboard note voltages and the note resistor network and they are ok, I am starting to worry that the fault is on the YM26600 ( key data producing circuit) or the YM26700 (key voltage detecting circuit).
Using an oscilloscope , I tried to detect the pulses on N1,N2,N3,N4 coming from YM26600 to the YM26700 but they dont have the pattern that is mentioned in the service manual. Normally by pressing C note, I should see a pulse on N1, and no pulse on N2,N3,N4, but in my case, I am getting pulses on N1 and N3.
Could it be that the YM26600 is shot ? Or could it be that the YM26700 is malfunctioning and it interferes with the operation of the YM26600
I am bit confused... Any ideas about how to check/diagnose the YM26600 and YM26700 properly ?
many thanks
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Re: Yamaha CS-50 calibration frustration (KAS board)

Postby Yekuku » Sun Sep 14, 2014 12:19 pm

Well after 5 months of troubleshooting, problem solved! :)
For future reference the irregular note tracking was caused by a bad Gate/integrator 4016 IC on the KAS board.
I had replaced all cmos IC's with new ones from the start but it seems i got a bad 4016. I really hate when this happens with new parts :evil:
Damn it, I am realizing how rare these YM26600 and YM26700 are becoming...
By the way the aftertouch in the CS-50 is amazing :o
Now lets get back and fix that mild distortion issue!
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