I have a “mostly working” Moog Source with a glitch. On most patches it keeps playing a “drone” sound.
I just got my Moog Source back from my Tech who
Volume pot cleaned, now is fine.
Replaced 5V regulators instead of just cleaning as I read they are a problem
Battery tested and determined OK not changed.
What I discovered is that the issue I have still is somehow tied to the Keyboard Tracking section. KB tracking can be OFF, 1/2 or Full.
On some of the patches, when I turn KB tracking off, the synth acts normally. And the continuous drone goes away.
Both OSC 1 and 2 and noise work and are fully adjustable, i can choose wave etc…ADSR works, arp works etc…
Any advice on what to check next that is I guess part of the KB tracking would be greatly appreciated.
If the memory back-up lithium battery is the original one (remember this synth dates back to 1981-82), even though it might still show close to 3.0 Volts that doesn’t mean it’s necessarily okay. It might not have sufficient power (milliamps) to sustain RAM content correctly when the synth is powered off.
Anyway, any tech who stumbles across a synth that has an over 30 years old Lithium battery shouldn’t take any chances and replace it. Because it could also eventually leak and wreak havoc on the PCB.
Unless, of course, the battery had already been replaced ? But the question remains: when was it done last ?
As for the keyboard problem, it could all be caused by corrupted RAM content if the problem is only on some patches. Looking at the schematics, the pitch CV (and filter keyboard tracking) seems to be generated by a DAC controlled by the CPU and ROM in the Moog The Source. Since the keyboard behaves normally on some patches and not others, I doubt that there’s anything wrong with the keyboard contacts, or keyboard circuit. It might be a defective quad switch CD4016 or CD4051 multiplexer in there somewhere (maybe U5 on the analog board ?), but I doubt it. I would strongly suggest taking it to a qualified tech, who has experience in fixing hybrid analog/digital 30 year old Moog synths.
You really need a new tech, because frankly he didn’t do sh!t.
If the RAM contents are corrupt, a corrupt patch can result in weird behavior. And those batteries are LONG past their expiration date - get it replaced!
It is also possible that one of the RAM ICs is bad. I uncovered a bad one in my OBSX, seems to be a common failure in other synths.
This requires science…