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Moog MG-1 fall time sustain problem
Posted: Wed Feb 13, 2013 11:18 pm
by gtivr6fan
Picked up two of these recently and other than the black "goo" they are in good shape other than a few dirty sliders which have been desoldered and cleaned and resoldered again. The one remaining issue is that when one of the MG-1's is switched to "contour" the "fall time" slider acts as a volume for a sustain, which is not on. The "rise time" works as it should. As mentioned already I have cleaned the sliders and that particular switch. I have checked it with the other one I have and that is not how it should work...obviously.
Any ideas?
Re: Moog MG-1 fall time sustain problem
Posted: Thu Feb 14, 2013 2:37 am
by thealien666
Possibly defective U14 (CD4007) maybe ?
Re: Moog MG-1 fall time sustain problem
Posted: Thu Feb 14, 2013 1:41 pm
by gtivr6fan
thealien666 wrote:Possibly defective U14 (CD4007) maybe ?
Would that be the case if the "rise time" still functions correctly?
Re: Moog MG-1 fall time sustain problem
Posted: Thu Feb 14, 2013 2:34 pm
by thealien666
The 4007 consists of three complementary pairs of MOS transistors. It's possible that only one pair is damaged or malfunctioning inside the chip.
It could also be the Sustain IN - OUT switch that isn't making proper contact. Check for proper operation on all pins with a multimeter.
If the switch is working correctly, then it could also be a defective (U13) 4558 (prone to failure).
When in doubt, replace. Very inexpensive.