Vintage Synth Repair

----- Original Message -----

From: jammie

To: vintagesynthrepair@yahoogroups.com

Sent: Sunday, November 11, 2012 7:13 AM

Subject: Re: [vintagesynthrepair] ARP Omni MK1 - no sound, must be something stupid

he said he replaced all the tantalum caps

----- Original Message -----

From: Paulo Palmieri

To: vintagesynthrepair@yahoogroups.com

Sent: Sunday, November 11, 2012 9:07 AM

Subject: Re: [vintagesynthrepair] ARP Omni MK1 - no sound, must be something stupid

There is a tantalum cap there in the oscillator around the MK5024 that kills the oscillator. It´s common issue finding this cap shorted.

----- Original Message -----

From: jammie

To: vintagesynthrepair@yahoogroups.com

Sent: Sunday, November 11, 2012 6:26 AM

Subject: Re: [vintagesynthrepair] ARP Omni MK1 - no sound, must be something stupid

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

----- Original Message -----

From: Mark

To: vintagesynthrepair@yahoogroups.com

Sent: Sunday, November 11, 2012 5:00 AM

Subject: [vintagesynthrepair] ARP Omni MK1 - no sound, must be something stupid

I 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!!!