OldSynths

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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