----- Original Message -----From: MarkSent: Sunday, November 11, 2012 5:00 AMSubject: [vintagesynthrepair] ARP Omni MK1 - no sound, must be something stupidI am in desperate need of some direction! I picked up a broken ARP Omni MK1 last year on craigslist as a project, because of the success I had read about online of people bringing them back from the grave.
There is no sound at all coming from this synth! I am a DIY hobbyist, but not much of a schematic jockey, so I have tried to restore and overhaul the Omni. The lights light up and the switches turn the lights on and off. The power supply is spitting out -15 and +15 like it should, just no output from the main out, synthesizer out, or any other out.
You guys are going to laugh.
I replaced the following:
-All tantalum caps, decoupling and envelope
-All CD4XXX ICs, on every board (yes, I have WAY too much time)
-LM1458s on string control board
-LM301 on filter board
Now I am at an impasse. I really want this thing working with a passion, and getting rid of it this far in the game would be a big mistake. Is there any part of the synth I should be looking at? I have an oscilloscope, should I be probing a certain place? I've worked on smaller, less complicated synths in the past, but the Omni is damn near confusing.
One last question: The phaser board connector was upside down when I received it. Is there anything that could fail on the phaser board that would cause it not to make any sound?
I truly appreciate your help, thank you so much for your time!!!
Message
Re: [vintagesynthrepair] ARP Omni MK1 - no sound, must be something stupid
2012-11-11 by jammie
first thing set you oscilloscope to the master
oscilator
and make sure your getting a square
wave
put it on pin 12 of the cd4007
this then goes to the top octave devider
chip
mk5024
if you have no square wave generated here you will
not get any output at all
if you have a square wave
then test the top octave devider chip pins
4/5/6/7/8/9/10/11/12/13/14/15/16
these are the square wave signals for the each key
note
if you dont have square waves at these pins then
the top octave chip is crapped
these are the first 2 places to look as seeing you
have changed so many items on this synth