Vintage Synth Repair

Hi Ed, 

You most likely have a dead short on either the pos or
neg 15 volt bus. You can verify this with an ohmmeter.
Disconnect the supply and measure from each bus to
ground. If it's less than a few hundred ohms you have
a shorted bypass capacitor across the bus. Where the
PS voltage connects to each of the boards in the Omni
you will find a silver dipped tantalum capacitor from
each bus to ground. Change every one of them to an
electrolytic of the same value. As for the power
supply you can substitute the power transistors that
you can't cross with a different package. It's not
important to use an exact match. If you want to just
replace the entire supply Digi-Key has new linear
supplies for around $40. I can find you a suitable
replacement and get back to you with the part number. 

Good Luck, 
Bob



--- Ed Hallborg <ehallborg@...> wrote:
> 
> 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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>
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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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> 
> 
> 
> 
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