Hi - I hope it’s ok to post technical questions here. If not, please let me know if you know of any forums that would be better.
My MultiMoog doesn’t make sound. I followed these instructions from the service manual:
Set controls to troubleshooting settings. Output is a very low level squeal, some warbling in it.
Step D: Shorted IC304 pin 2 to ground and oscillator runs.
Step G:
Vo at P2 pin 3 = 14.69V
IC301 pin 1 = -10.6V
IC306 shorted each pin to ground:
1 - arc, short
2 - unchanged
3 - unchanged
4 - unchanged
5 - unchanged
6 - yes signal
7 - yes signal, frequency halved
8 - output killed
9 - unchanged
10 - unchanged
Is the IC306 resistor network the culprit? I can’t find it available anywhere. Could I fabricate the same thing from discrete resistors?
I’d appreciate any help and thank you for reading this.
Sorry if I don’t replicate all of your troubleshooting here by the book, but I would like to say that the CTS ceramic resistor arrays used in Micros, Multis and others like the last rev of Mini D VCO boards, I have started to notice are failing more often.
Years ago, it was rare to ever encounter a bad one.
In the past few years, I’ve seen about 4 or 5 die.
I have been fortunate enough to have had other boards I could take them from, but you might have to make your own from separate resistors.
If you do, use very precise resistors.
0.1% is not overkill.
Resistor arrays are usually very, very precise, even the ones made 30 years ago.
Also analyze the circuit to see if what Moog was desiring was precision or matching.
Sometimes it makes sense to buy one $1.00 0.1% resistor and sometime it’s wiser to buy 200 1% ones for $4.00
Thanks for your advice Kevin. I looked at mouser.com and the only 1% resistors with the necessary resistances are metal film. I assume that’s ok. What power rating do you recommend?