Vintage Synth Repair

hi all,

i was wondering if anyone had any hints about diagnosing some remaining
problems on my omni mk1...the problems are (in order of importance):

-long release on notes 22-28 (A-Eb) even when release slider is at 0...i
get short release on all other notes except these, which release as if the
slider were at about 50%...

-violin/viola switching is messed up: when viola is on and violin is off,
i get violin+viola from key 21-29, viola only from 30-39, and nothing from
40-49; when violin is on and viola off, i get nothing from 21-29, violin
from 30-39, and both from 40-49...(of course, the same holds true
for 4'/8' synth voices...)

-problems in bass section: 16' voice not working...when 8' bass (or cello)
is selected, it sounds like all pitches are gating all at once when i
press any key on the bass end of the kbd...

what i have done so far:

-replaced all cmos 4000-series chips on upper & lower voicing boards (but
not on synth/phaser/control boards)

-replaced all tantalum caps on upper/lower voicing bds

-cleaned/reassembled release slider

-replaced 22 uF tantalum caps on string control board (this fixed long
release problem which existed for all notes on kbd, not just 22-28)

thanks, PB>>

-- 
Peter Brown                 Senior Software Engineer
Dept. of Computer Science        140 Governors Drive
University of Massachusetts   Amherst, MA 01003-4610
Phone: (413) 577-2505            Fax: (413) 545-1249
pbrown@...  http://www.cs.umass.edu/~pbrown
----------------------------------------------------
               ARP Omni Resource Page
       http://parsley.cs.umass.edu/pbrown/arp
----------------------------------------------------

Hello  All

> replaced all cmos 4000-series chips on upper & lower voicing boards (but
> not on synth/phaser/control boards)

I'd replace these as well, not so much on the phaser PCB.
The control pcb's do a lot of switching using 4016's or 4066's I think.
If you have a scope you can look at the phasor pcb to make sure all audio
signals are getting through.
On my omni, one of the MN 3002's was defective and only 2 audio paths were
getting through.

I also will wash all PCB's with very warm, lightly soaped water.
I even put in a minute amount of orange glow as well.
Then I rinse off very well with water.
I also clean and spray water into the slidepots as well.
Some folks  will rinse with alcohol to further evaporate the water.
I usually don't.
Instead I'll put the pcb's in a sunny window to dry or put them in my gas
oven.
The pilot keeps it warm but not hot..
I put the boards in component side up and alternate with component side
down.
I'll let it dry as long as it takes.
You can speed it along with a hair dryer on low heat.

After all this, the sliders are usually stiff.
I apply cramolin red, then blue to further clean then lube the sliders.
www.caig.com  is where you'll find good cleaning solutions.
I have 2 more Omni's to fix and if I run across the same problems you are
having, I'll
try to fix and post here.
By the way, your Omni site looks good.
Most of the info about changing the tantalum caps and IC's is right on.

Thanks
Kim S

-- Original Message -----

From: "Peter Brown" <pbrown@...>
To: <oldsynth@yahoogroups.com>; <vintagesynthrepair@yahoogroups.com>
Sent: Tuesday, February 19, 2002 12:39 PM
Subject: [vintagesynthrepair] remaining omni problems


> hi all,
>
> i was wondering if anyone had any hints about diagnosing some remaining
> problems on my omni mk1...the problems are (in order of importance):
>
> -long release on notes 22-28 (A-Eb) even when release slider is at 0...i
> get short release on all other notes except these, which release as if the
> slider were at about 50%...
>
> -violin/viola switching is messed up: when viola is on and violin is off,
> i get violin+viola from key 21-29, viola only from 30-39, and nothing from
> 40-49; when violin is on and viola off, i get nothing from 21-29, violin
> from 30-39, and both from 40-49...(of course, the same holds true
> for 4'/8' synth voices...)
>
> -problems in bass section: 16' voice not working...when 8' bass (or cello)
> is selected, it sounds like all pitches are gating all at once when i
> press any key on the bass end of the kbd...
>
> what i have done so far:
>
> -replaced all cmos 4000-series chips on upper & lower voicing boards (but
> not on synth/phaser/control boards)
>
> -replaced all tantalum caps on upper/lower voicing bds
>
> -cleaned/reassembled release slider
>
> -replaced 22 uF tantalum caps on string control board (this fixed long
> release problem which existed for all notes on kbd, not just 22-28)
>
> thanks, PB>>
>
> --
> Peter Brown                 Senior Software Engineer
> Dept. of Computer Science        140 Governors Drive
> University of Massachusetts   Amherst, MA 01003-4610
> Phone: (413) 577-2505            Fax: (413) 545-1249
> pbrown@...  http://www.cs.umass.edu/~pbrown
> ----------------------------------------------------
>                ARP Omni Resource Page
>        http://parsley.cs.umass.edu/pbrown/arp
> ----------------------------------------------------
>
>
>
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