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I would be pretty sure that the regulator wouldbe the standard 723 adjustable type. ARP used this on a lot of their synths andused the same circuit configuration. If you pull up the 723 pin-out you shouldbe able to compare with the schematic. If only the negative rail is bad then it’slikely that the associated op-amp (probably a 301!) is what needs replacing.
I would also take the opportunity to replaceany tantalum polarized caps in the regulator circuit – use electrolytictypes or heavily de-rated new tantalums
mw
-----Original Message-----
From: Bob Weigel[mailto:sounddoctorin@...]
Sent: Saturday, November 01, 200312:35 PM
To: oldsynths@yahoogroups.com
Subject: Re: [oldsynths] Re: ARPPro Soloist problems, part 2
Hmm. Not likely. It's probably theregulator. The trim pot could have
some effect in certain types of circuits eventhough the regulator is blown.
If you know what the voltage is supposed to be, Ithink you said -15V...you
could just replace with a 7915 while cutting out all related parts of that
circuit except the input capacitance and an outputcapacitance of at least
a.1uF to kill oscillation. Usually thosecircuits use a local .1cap and
then nearer the components being driven put a 10uFelectrolytic or like
that. Anyway, your other regulator MAY haveassociated components like a
resistance and maybe a diode in a leg that goes toground. You direct
ground the 7915. Remember it's a negativeregulator so put the negative of
any cap towards it's output rather than ground!
Anyway working renditions of that numberthrough Sam's software, I get no
cross ref. It's some oem number it soundslike. Nothing I've ever seen.
78xx and 79xx chips are rated for a little over anamp usually if they have
a great heat sink. So usually one has plentyof current capacity to feed 50
chips or like that doing 10 to 20ma each. -Bob
----- Original Message -----
From: "dshoemaker93"<dgsaa@...>
To: <oldsynths@yahoogroups.com>
Sent: Saturday, November 01, 2003 10:54 AM
Subject: [oldsynths] Re: ARP Pro Soloist problems,part 2
> Hi,
>
> Thanks for the tips, Bob. Concerning the regulator--which I'm assuming I
need to
> replace--I've been trying to find a modernreplacement--is there a easy
way to do
> that? It's listed in the schematic as aFairchild U5R 7723393, and it's
an IC. I can't
> find that part number at Digikey or NTE oreven the Fairchild website.
Any tips?
>
> Also, the trim pot for the negative voltageonly trims it down to
about -18.5. Does
> this mean it could be the ∗trimpot∗ that'sblown and not the regulator
itself?
>
> --David
>
>
> --- In oldsynths@yahoogroups.com, "BobWeigel" <sounddoctorin@m...> wrote:
> > Yow, I'ddouble check that -19V! BE CAREFUL THOUGH! Some of those
> > chips may be rated for 15V...I can'trecall...surely a 301 isn't rated
for
> > more than 18V I don't think. Pretty old chip. My farfisa organ got a
> > couple tos chips knocked out and I hadto buy retro modules for it which
> > were expensive...due to a badregulator. But before you turn it on get
> > ready to turn the powersupply adjustmentand slowly turn it to make sure
you
> > don't go the wrong way immediately onturn on and get that set right.
> >
>
>
>
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