Without seeing the circuit, I don't have much to offer... it could be that op 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...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 > > > > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Sponsor > > > > ADVERTISEMENT > > > > Click Here! > > > > <http://rd.yahoo.com/M=244522.3707890.4968055.1261774/D=egroupweb/ > > S=1705032144:HM/A=1595055/R=0/SIG=124j83ehr/*http://ashnin.com/clk/ > > muryutaitakenattogyo?YH=3707890&yhad=1595055> > > > > > > > > > > > > > > > > To unsubscribe from this group, send an email to: > > > > oldsynths-unsubscribe@yahoogroups.com > > > > > > > > > > > > > > > > Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service > > > > <http://docs.yahoo.com/info/terms/>. > > > > > > > > To unsubscribe from this group, send an email to: > > oldsynths-unsubscribe@yahoogroups.com > > > > > > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > > > > > > > > > > > > > To unsubscribe from this group, send an email to: > oldsynths-unsubscribe@yahoogroups.com > > > > Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service > <http://docs.yahoo.com/info/terms/>.
Message
Re: [oldsynths] Re: ARP Pro Soloist tech question
2003-10-29 by Ed Edelenbos