Without seeing the circuit, I don't have much to offer... it could be thatop amp (in's are right, out is wrong) or something connected to it, a cap, transistor, the next opamp, or...
Ed
Bob Weigel wrote:
A quick tip...ifyou simply probe all outputs of op amps in the general area
of a problem, you will often find one that has slid to rail voltage. Look
at the diagram and see if this might be an appropriate state for that one
and/or check the inputs to see if their voltage state supports the rail
state you see (ie. non-inverting higher than inverting gives + rail andvisa
versa..) Sometimes you'll find a bad op amp this way. I don't know that
circuit at all so good luck. -Bob
----- Original Message -----
From: "dshoemaker93" <dgsaa@...>
To: <oldsynths@yahoogroups.com>
Sent: Wednesday, October 29, 2003 10:47 AM
Subject: [oldsynths] Re: ARP Pro Soloist tech question
> Hi,
>
> Checking my schematics, I see that this is indeed a "scanned' keyboard.
The key and
> octave codes are sent to the d/a converter, and then through a
differential
> amplifier to the VCO circuit.
>
> Here's what I found:
>
> 1. Output from keyboard produces the correct voltages at the correct
keys.
> 2. Output from d/a converter shows same correct voltages
> 3. Input into differential amplifier shows same voltages, suggestingno
broken circuit
> path.
>
> and
>
> 4. Output from the Differential amplifier (either an LM301 or SL19988op
amp) is a
> CONSTANT 15 volts or so.
>
> Seems to me this suggests that particular op amp is dead. Yes?
>
> Thanks,
> David
>
>
> --- In oldsynths@yahoogroups.com, Ed Edelenbos <eded@s...> wrote:
> > I don't have any Soloist info... not even a block diagram butif you
> > are getting a low note and lower when the octave down button ison, then
> > it souds like the osc. and octave button are working but the cvfrom the
> > kb and tuning knob are not making it to the osc. cv input. IfI
> > remember correctly, there are no "scanning chips...". It is asimple
> > voltage divider (probably 100 ohm reisistor at each key contactwith the
> > high voltage end controlled by the tuning knob) and the outputof that
> > is not making it to the cv in of the osc. or the cv input sectionof the
> > osc. is blown.
> >
> > I've seen various sources for schematic onthe web... the thingto do
> > would be to find the output of the keyboard voltage and measureit to
> > see if it changes as you hit different keys and then trace thatsignal
> > to the osc. and see where the signal quits. I would bet a brokenwire.
> >
> > Ed
> >
> > dshoemaker93 wrote:
> >
> > > Hi Ed,
> > >
> > > Are you suggesting that the keyboard scanning chips mightbe the
> > > culprit? Sending
> > > no note/octave information? Or do you mean that no voltage∗at all∗
> > > is reaching the
> > > oscillator?
> > >
> > > Thanks,
> > > David
> > >
> > > --- In oldsynths@yahoogroups.com, Ed Edelenbos <eded@s...>wrote:
> > > > Sounds to me like the V into the osc. isn't making it...
> > > >
> > > > Ed
> > > >
> > > > David Shoemaker wrote:
> > > >
> > > > > Hi everyone,
> > > > >
> > > > > I took delivery on my ARP Pro Soloist today. Iknew it would need
> > > > > repairs when I bought it, and here's what I'vediscovered so far.
I
> > > > > would really appreciate any suggestions on thenext
diagnostic/repair
> > > > > steps. I have a hunch this is not going to bethat complicated.
> > > > > (crossing fingers)
> > > > >
> > > > > Here's the problem: It powers up correctly. Everykey triggers a
> > > > > sound, but the pitch does not change from key tokey. The sound
it
> > > > > ∗does∗ make is a very low cycle tone, much lowerthan any keyboard
> > > > > should make. It does not seem to be an LFO, because: The pitch
> > > > > changes in octaves (roughly) as I move the octaveshift lever.
Of
> > > > > course, the pitch is so low to start with thatthe "normal" and
"low"
> > > > > octave settings are just clicks. The pitch doesNOT change, as
far as
> > > > > I can tell, when I adjust the tuning trimpot, nordoes it respond
to
> > > > > the front panel tune "knob".
> > > > >
> > > > > The preset switches DO change the timbre of thesound, as if the
> > > > > filters are working correctly. The volume sliderworks normally.
The
> > > > > "touch sensitivity" switches act as they shouldEXCEPT for the
pitch
> > > > > bend, and possibly the vibrato (hard to tell withsuch a low pitch
> > > > > though). Portamento does NOT seem to work.
> > > > >
> > > > > The presets I would expect to be in a lower octaveseem to be so,
e.g.
> > > > > "Bass", "Tuba".
> > > > >
> > > > > What I've done so far:
> > > > >
> > > > > --I replaced the aluminum caps in the power supply,and the output
> > > from
> > > > > the power supply is normal.
> > > > > --I very carefully cleaned all the oxidation offthe J-wires and
the
> > > > > contact bar. Key triggering is almost perfectas far as I can
tell.
> > > > >
> > > > > Can anyone offer any suggestions? I have a couplesources for
spare
> > > > > parts if I need them--I'm just not sure what totest/fix next.
> > > > >
> > > > > Thanks very much,
> > > > > David Shoemaker
> > > > >
> > > > >
> > >
> > >
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