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Thread

VCF pot + MG to VCF not working

2017-02-03 by space4box@hotmail.com

Hello all,

My polysix Cutoff knob started not to work as it should.The knob does not working and MG to VCF is not working too.I can control the VCF with KBRD TRACK knob.Some times after one hour turned on,the VCF and MG to VCF start to work again as should.But lately i see it less and less.

Thanks for reading and your help!

Steve

Re: VCF pot + MG to VCF not working

2017-02-04 by a_cornish_2000@yahoo.com

IIRC the pots run on a +/-5v signal, which is multiplexed through IC1 & 2 (14051) to a data line. The control signal turns up again at the output pins of IC18 & IC19 on the KLM-367. Anywhere in that chain may be the problem.
In my case, the KLM-370 had corroded so control signals were not getting through. A lot of repairing traces had to be done.

Your first step would be to check the voltage swings between +/-5v going in to IC1 on pin 14.
To check it is on the data line, you'll need an oscilloscope.
Then check pin 14 on IC18 on the KML-367, as it should be the same as pin 14 on IC1

Anthony,