cs40m acts weird

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radek tymecki
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cs40m acts weird

Post by radek tymecki » Mon Mar 22, 2010 8:55 pm

i've managed to fix some things in cs40m but it still acts weird.

the knobs are not corresponding - i move em and still i can hear weird sounds comming out of it

keyboard works, pitch knobs also, modwheel too

the thing that is not working: vco, vcf, vca, eg sections

what can cause problems? psu is fine. zener diodes?... i've changed most of 4xxx cmos chips
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rikusk
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Re: cs40m acts weird

Post by rikusk » Wed Mar 24, 2010 7:21 pm

Hi,

I had same problem and the reason was failed uPC271C / LM311 comparator (IC8) on PGM-board.
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Steve Jones
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Re: cs40m acts weird

Post by Steve Jones » Thu Mar 25, 2010 1:20 pm

rikusk wrote:Hi,

I had same problem and the reason was failed uPC271C / LM311 comparator (IC8) on PGM-board.
That sounds like a very good place to start looking. A-D converter S/H section on the PGM board.
Synthesizer service tech since 1982.
Synth parts and service, Sydney Australia.
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Re: cs40m acts weird

Post by radek tymecki » Sat Mar 27, 2010 12:47 am

ok :) i'll try to replace it and see what will happen then :)
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Re: cs40m acts weird

Post by radek tymecki » Sun Mar 28, 2010 7:50 pm

ok i've exchanged lm311. knobs are now reacting! :D

but still, sound is crunchy/gritty and when i touch keyboard keys it doesn't change pitch
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Steve Jones
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Re: cs40m acts weird

Post by Steve Jones » Sun Mar 28, 2010 9:24 pm

Check the CV output jacks (JK1 and JK2) with a meter and see if there are sensible control voltages coming out as you play up and down the keys, if not the problem will be on the SK board.
Synthesizer service tech since 1982.
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radek tymecki
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Re: cs40m acts weird

Post by radek tymecki » Mon Mar 29, 2010 9:21 pm

what components could be faulty?
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Re: cs40m acts weird

Post by radek tymecki » Thu Apr 22, 2010 8:02 pm

any ideas?
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Re: cs40m acts weird

Post by radek tymecki » Fri May 14, 2010 6:03 pm

ok i've noticed few things. there are some bugs on boards which are connected to C2 and C3 on DC.

so there's:
- 1 V drop on VCO board
- 0.5 V drop on MOD board
- 0.7 V drop on DM board
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