hi guys, wondering if you may be able to help.upon further research into am M-board VCF envelope issue both myself and scott are sharing, i found that the problem is the once the envelope opens, it NEVER closes. i realized that when first powered up, the problem voice card envelope opens properly. it just stays open. so when the voice rotation comes back to it, its still open, hence it sounding like the sustain level is set to an astronomical amount. more specs:-almost definitely not IG00152. tried with new working chip, and same problem.-almost definitely not VR 15,18, or 19. replaced VR18(sustain level), and checked impedance of VR 15 and 19. both working.this leads me to believe that there is failure of another part on the m-board. does anyone know these well enough to take an educated guess here? thanks guys!
I don't see any obvious cause. The sustain level on the filter EG is always zero - the pin is tied to ground - so I don't know how how the EG could be stuck open. Since this is a static/stuck problem, you should be able to trace this with just a voltmeter. I'd pop out the bad board and the same voice card in the other set of eight, set the panel to the same settings and compare voltages. I'd check the control inputs to the EG (AF, DF, RF, AL, IL), the output off the EG (IC 12, pin 3 = TP1). See
http://www.therogoffs.com/cs80/pics/page%2041%20-%20M%20Circuit%20Diagram.jpg and
http://www.therogoffs.com/cs80/pics/page%2044%20-%20M11-12%20Circuit%20Board%20&%20Wiring.jpg).
It would also be handy if you and Scott could record an audio sample of a good and bad note and put them up in the Files section of the website.
David
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