Vintage Synth Repair

Well I am certainly not impressed with your local tech! ARP's are (apart
from the sliders) some of the easiest vintage synths to fix. Just about all
of the parts are still easy to find. Even the top-octave divider in the Omni
can still be found.

 

Oberheims are probably a little easier since they generally socket all of
the IC's :-)

 

I've tried looking for the schematics on-line and the site where I found
them previously seems to be dead. Can you or someone e-mail me the power
supply schematic? I'll take a look and let you know if there are any issues
with parts. I'll try and give you a source for them as well. 

 

By the way, if the transformer is OK, an adequate power supply for this
beast could be designed and built by a half-competent tech in about an hour
and for less than $20 parts cost.

 

However, the most likely problem causing the power supply to fail is bad
tantalum decoupling caps on the other boards. This is a typical problem on
many pieces of electronics from this era. The timing caps on the voicing
boards can also fail and drag down the power supply. If we can get the power
supply working I can try and talk you through finding problems on the other
boards.

 

mw

-----Original Message-----
From: Ed Hallborg [mailto:] 
Sent: Friday, September 12, 2003 6:11 AM
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Digest Number 508

 

Thanks Massada  for  your input on this.  This has been an ongoing
problem...I got this thing probably a year ago it looks great but gets no
sound at all.  I did some checking on it, got the schematics and found that
it appears to have a bad - 15 voltage regulator.  So I try and order the
part, it has to cross to this and than cross to this and etc.  Finally I get
a pair of regulators that should work, I put one in and it works momentarily
and fails toasting a resistor on the way.  I take it to a local tech...They
keep it two months and return it unrepaired, they cant find the -15 voltage
regulator and suggest designing a new power supply for it - but don't seem
eager to do it.  Mainly they tell me not to come back unless "I bring in
something from after 1970".  So now I'm back where I started with the damn
thing sitting in the corner of the studio collecting dust.  At this point
I'm looking for anything and 

Regards,

Ed

 

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Message: 2
Date: Thu, 11 Sep 2003 10:14:39 -0700
From: "masada wilmot" 
Subject: RE: OMni 2 Powersupply repair cont...

Hello all,



I'm a fairly new lurker on here but I feel the need to pipe in on this
thread. As I recall, the power supplies on the Omni are a simple standard
design with no exotic components. If the transformer is still OK, replacing
the active components would not cost more than $5 and you would not have to
install a mechanically different subsystem.



I've just repaired a Quadra supply that was just a standard
723/op-amp/TIP110-115 circuit. I haven't looked at the Omni for quite some
time but I expect that it is the same. Am I missing something here that went
before?



mw



PS, a supply that is capable of putting out more amps than you need is
normally not a problem. However, beware the supplies that require a minimum
load on one rail to maintain regulation - usually switchers.







-----Original Message-----
From: Ed Hallborg [mailto:ehallborg@...] 
Sent: Thursday, September 11, 2003 7:35 AM
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] OMni 2 Powersupply repair cont...



Robert,



Here's the only thing I found so far that meets your specs.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem
0> &item=2556349463&category=32720



Is this or something like it usable? I have done some google searches and
found the whole power supply boards but they seem like they are putting out
too many amps. I don't know if thats a problem or not---also the ones I
found on mouser.com are about 100$ apiece. That's fine if it will work.



Regards,

Ed

Message: 1
Date: Sat, 6 Sep 2003 08:36:27 -0700 (PDT)
From: Robert Benchic 
Subject: Re: Subject: Re: another broken omni 2

Ed, 

You would be replacing the entire power supply
eliminating the need to repair the regulator in the
original. The connections would be easy, positive and
negative 15 volts DC with a common ground and 115
volts AC. I can find you a supplier and appropriate
model if you like. 

-Bob


--- Ed Hallborg wrote:
> Thanks Robert,
> 
> Can you tell me anymore about these? I'm a bit
> confused as too whether they will take care of the
> -15 voltage regulator problem in the omni 2. Do
> they bypass the regulator or something. Is their a
> special procedure to hook them up?
> 
> Thanks,
> Ed
>
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