> A quick tip...if you 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
> and visa
> 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, suggesting no
> broken circuit
> > path.
> >
> > and
> >
> > 4. Output from the Differential amplifier (either an LM301 or
> SL19988 op
> 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 but if you
> > > are getting a low note and lower when the octave down button is
> on, then
> > > it souds like the osc. and octave button are working but the cv
> from the
> > > kb and tuning knob are not making it to the osc. cv input. If I
> > > remember correctly, there are no "scanning chips...". It is a simple
> > > voltage divider (probably 100 ohm reisistor at each key contact
> with the
> > > high voltage end controlled by the tuning knob) and the output of that
> > > is not making it to the cv in of the osc. or the cv input section
> of the
> > > osc. is blown.
> > >
> > > I've seen various sources for schematic onthe web... the thing to do
> > > would be to find the output of the keyboard voltage and measure it to
> > > see if it changes as you hit different keys and then trace that signal
> > > to the osc. and see where the signal quits. I would bet a broken
> wire.
> > >
> > > Ed
> > >
> > > dshoemaker93 wrote:
> > >
> > > > Hi Ed,
> > > >
> > > > Are you suggesting that the keyboard scanning chips might be 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. I knew it
> would need
> > > > > > repairs when I bought it, and here's what I've discovered so
> far.
> I
> > > > > > would really appreciate any suggestions on the next
> diagnostic/repair
> > > > > > steps. I have a hunch this is not going to be that complicated.
> > > > > > (crossing fingers)
> > > > > >
> > > > > > Here's the problem: It powers up correctly. Every key
> triggers a
> > > > > > sound, but the pitch does not change from key to key. The sound
> it
> > > > > > *does* make is a very low cycle tone, much lower than any
> keyboard
> > > > > > should make. It does not seem to be an LFO, because: The pitch
> > > > > > changes in octaves (roughly) as I move the octave shift lever.
> Of
> > > > > > course, the pitch is so low to start with that the "normal" and
> "low"
> > > > > > octave settings are just clicks. The pitch does NOT change, as
> far as
> > > > > > I can tell, when I adjust the tuning trimpot, nor does it
> respond
> to
> > > > > > the front panel tune "knob".
> > > > > >
> > > > > > The preset switches DO change the timbre of the sound, as if the
> > > > > > filters are working correctly. The volume slider works
> normally.
> The
> > > > > > "touch sensitivity" switches act as they should EXCEPT for the
> pitch
> > > > > > bend, and possibly the vibrato (hard to tell with such a low
> pitch
> > > > > > though). Portamento does NOT seem to work.
> > > > > >
> > > > > > The presets I would expect to be in a lower octave seem 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 off the J-wires and
> the
> > > > > > contact bar. Key triggering is almost perfect as far as I can
> tell.
> > > > > >
> > > > > > Can anyone offer any suggestions? I have a couple sources for
> spare
> > > > > > parts if I need them--I'm just not sure what to test/fix next.
> > > > > >
> > > > > > Thanks very much,
> > > > > > David Shoemaker
> > > > > >
> > > > > >
> > > >
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