Rhodes Chroma Polaris

i finally did the memory upgrade on my polaris--- it was very easy. but upon doing all sorts of tests to prove its ok i noticed that the touch sensitivity was out on voice #1 -- It played fine but every sixth note would NOT play with a soft touch... just a harder one. I did the voice isolation test and indeed voice 1 would not play softly. would this be an issue with a chip or connection in Voice #1? or in the keyboard? I had cleaned all the contacts, all notes do play.

> From: wasteking1
>
> i finally did the memory upgrade on my polaris--- it was very
> easy. but upon doing all sorts of tests to prove its ok i noticed
> that the touch sensitivity was out on voice #1 -- It played
> fine but every sixth note would NOT play with a soft touch...
> just a harder one. I did the voice isolation test and indeed
> voice 1 would not play softly. would this be an issue with a
> chip or connection in Voice #1? or in the keyboard? I had
> cleaned all the contacts, all notes do play.

My guess would be something around the volume sample-and-hold circuit,
causing its output to have a negative bias on it. You could test this by
selecting a steady (non-decaying) sound, and turning the volume parameter
down, and note if that particular voice disappears before the slider gets to
the bottom. I've seen excessive leakage in the 4051 switches (Zx01 or Zx02),
as well as failures in the capacitors (Cx35). Could even be the FET buffer
(Zx03) or the Curtis chip (Zx09), but that's less likely. You could check
the volume control voltage (Zx03B output) with a voltmeter, although a scope
might reveal a negative-going sawtooth wave at the sample-and-hold update
rate, if there's leakage.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:

>
> > From: wasteking1
> >
> > i finally did the memory upgrade on my polaris--- it was very
> > easy. but upon doing all sorts of tests to prove its ok i noticed
> > that the touch sensitivity was out on voice #1 -- It played
> > fine but every sixth note would NOT play with a soft touch...
> > just a harder one. I did the voice isolation test and indeed
> > voice 1 would not play softly. would this be an issue with a
> > chip or connection in Voice #1? or in the keyboard? I had
> > cleaned all the contacts, all notes do play.
>
> My guess would be something around the volume sample-and-hold circuit,
> causing its output to have a negative bias on it. You could test this by
> selecting a steady (non-decaying) sound, and turning the volume parameter
> down, and note if that particular voice disappears before the slider gets to
> the bottom. I've seen excessive leakage in the 4051 switches (Zx01 or Zx02),
> as well as failures in the capacitors (Cx35). Could even be the FET buffer
> (Zx03) or the Curtis chip (Zx09), but that's less likely. You could check
> the volume control voltage (Zx03B output) with a voltmeter, although a scope
> might reveal a negative-going sawtooth wave at the sample-and-hold update
> rate, if there's leakage.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...


>I tried your suggested volume test with a long sustained sound and the volume slider --it seemed to attenuate in a normal way-- no early cut out. and i repeat, the non-touch sensitive playing is fine

I was wondering if each of the 6 voices had a seperate chip(?) that dealt with interpereting the volume of the touch sensitivity signal that wouldnt affect the normal full signal. [would that be the Zx09?] is this touch /volume located in the sample/hold area? I have the schematics, but that doesnt really descrbe the function of the various parts. [ I also have a dead polaris to scavenge chips from if that would be helpful ] sorry, but i have no scope, just a meter.

> From: wasteking1
>
> I tried your suggested volume test with a long sustained sound
> and the volume slider --it seemed to attenuate in a normal way--
> no early cut out. and i repeat, the non-touch sensitive playing is fine
> I was wondering if each of the 6 voices had a seperate chip(?)
> that dealt with interpereting the volume of the touch sensitivity
> signal that wouldnt affect the normal full signal. [would that
> be the Zx09?] is this touch /volume located in the sample/hold
> area? I have the schematics, but that doesnt really descrbe the
> function of the various parts. [ I also have a dead polaris to
> scavenge chips from if that would be helpful ] sorry, but i have
> no scope, just a meter.

When you say "volume slider", I wonder if you're talking about the Master
Volume. I was talking about the Volume parameter in the Assignable Control
section. The Master Volume manipulates the gain of the single amplifier on
the output board, and has nothing to do with the sample-and-holds or the
individual channels.

All interpretation of touch sensitivity is done inside the CPU; it merely
delivers a single control voltage to each channel for Pitch A, Pitch B,
Width A, Width B, Cutoff and Volume. I can't imagine any mechanism that
would allow these to function normally for non-touch-sensitive sounds, but
function unevenly on touch-sensitive sounds in a way that correlates with
the voice number as opposed to the key number.

With no notes sounding, the voltage on pin 7 of all six Zx03 chips should be
slightly negative; if it's much more negative on the voice in question, then
you've narrowed the problem considerably. This can be tested with a
voltmeter.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:

>
> > From: wasteking1
> >
> > I tried your suggested volume test with a long sustained sound
> > and the volume slider --it seemed to attenuate in a normal way--
> > no early cut out. and i repeat, the non-touch sensitive playing is fine
> > I was wondering if each of the 6 voices had a seperate chip(?)
> > that dealt with interpereting the volume of the touch sensitivity
> > signal that wouldnt affect the normal full signal. [would that
> > be the Zx09?] is this touch /volume located in the sample/hold
> > area? I have the schematics, but that doesnt really descrbe the
> > function of the various parts. [ I also have a dead polaris to
> > scavenge chips from if that would be helpful ] sorry, but i have
> > no scope, just a meter.
>
> When you say "volume slider", I wonder if you're talking about the Master
> Volume. I was talking about the Volume parameter in the Assignable Control
> section. The Master Volume manipulates the gain of the single amplifier on
> the output board, and has nothing to do with the sample-and-holds or the
> individual channels.
>
> All interpretation of touch sensitivity is done inside the CPU; it merely
> delivers a single control voltage to each channel for Pitch A, Pitch B,
> Width A, Width B, Cutoff and Volume. I can't imagine any mechanism that
> would allow these to function normally for non-touch-sensitive sounds, but
> function unevenly on touch-sensitive sounds in a way that correlates with
> the voice number as opposed to the key number.
>
> With no notes sounding, the voltage on pin 7 of all six Zx03 chips should be
> slightly negative; if it's much more negative on the voice in question, then
> you've narrowed the problem considerably. This can be tested with a
> voltmeter.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>

you were right--i was testing with the master volume slider--- using the
assignable volume it cuts out at about 40% of the way up . At the risk of
sounding even more stupid-- i was wondering how i would check for negative
voltage --crossing pin 7 with what? ground? and my simple anaolg needle
radioshak meter showed +3 volts when i crossed from the battery to pin 7 on all zx03 chips. [ but i could try swapping Zxo3 chips if they are the likely source] ..i assume
that voices 1-6 correspond to chips numbered z2o3-z703 in the 'X' place . of
course that places chip Z203 under the output board requiring unscrewing the
whole main circuitboard.

> From: wasteking1
>
> you were right--i was testing with the master volume slider--- using the
> assignable volume it cuts out at about 40% of the way up . At the risk of
> sounding even more stupid-- i was wondering how i would check for negative
> voltage --crossing pin 7 with what? ground? and my simple anaolg needle
> radioshak meter showed +3 volts when i crossed from the battery
> to pin 7 on all zx03 chips. [ but i could try swapping Zxo3
> chips if they are the likely source] ..i assume
> that voices 1-6 correspond to chips numbered z2o3-z703 in the 'X'
> place . of
> course that places chip Z203 under the output board requiring
> unscrewing the
> whole main circuitboard.

To measure negative voltages with an analog meter, just connect the positive
input to the meter to ground somewhere, and use the negative input to probe
the op-amp outputs; the negative voltages will show up as positive values on
the meter. If you have a digital meter, then it'll have a minus sign.

If the chips are socketed, then, yes, swapping them is a good way to find
bad chips. It's unlikely to be the capacitors, because leaky capacitors pull
the voltage toward ground, not toward the minus rail.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:

>
> > From: wasteking1
> >
> > you were right--i was testing with the master volume slider--- using the
> > assignable volume it cuts out at about 40% of the way up . At the risk of
> > sounding even more stupid-- i was wondering how i would check for negative
> > voltage --crossing pin 7 with what? ground? and my simple anaolg needle
> > radioshak meter showed +3 volts when i crossed from the battery
> > to pin 7 on all zx03 chips. [ but i could try swapping Zxo3
> > chips if they are the likely source] ..i assume
> > that voices 1-6 correspond to chips numbered z2o3-z703 in the 'X'
> > place . of
> > course that places chip Z203 under the output board requiring
> > unscrewing the
> > whole main circuitboard.
>
> To measure negative voltages with an analog meter, just connect the positive
> input to the meter to ground somewhere, and use the negative input to probe
> the op-amp outputs; the negative voltages will show up as positive values on
> the meter. If you have a digital meter, then it'll have a minus sign.
>
> If the chips are socketed, then, yes, swapping them is a good way to find
> bad chips. It's unlikely to be the capacitors, because leaky capacitors pull
> the voltage toward ground, not toward the minus rail.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>

well i made a mess now
i first tried swapping all 5 chips (01.02,03,04,05) in the sample and hold area betwwen the Z2 (voice 1) and Z6 (voice 5)-- no change in the touch sensitivity problem. so i had this great fear that the voices were inverted and maybe voice 1 was actually the Z7 row(actually voice 6)...so i pulled out a chip to see if voice 6 would or wouldnt work-- it didnt sound so i put the chip back having confirmed that it was indeed voice 6... but now voice 6 is all messed up-- it plays only a click on all keys till the c sharp in the 4th octave then itplays a loud tone (but not the patch) then above this i get just a quiet high pitch tone on all notes above. I tried switching ALL chips between voice 5 and 6 but no change -- i seem to have killed voice 6 and still have the problem with voice 1-- any great ideas here??

good news---i got my voice 6 to operate normally again ultimately by just doing a 'tune all' ... i have NO idea what happenned, but im glad its back all i knew was that NO chips were bad . anyhow, i still have no idea what controls the touch sensitivity on each voice. it does NOT appear to be the 4 socketed chips in the sample hold area. but that problem is minimal compared to loosing a whole voice.

--- In chromapolaris@yahoogroups.com, "wasteking1" <wasteking1@...> wrote:
>
>
>
> --- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@> wrote:
> >
> > > From: wasteking1
> > >
> > > you were right--i was testing with the master volume slider--- using the
> > > assignable volume it cuts out at about 40% of the way up . At the risk of
> > > sounding even more stupid-- i was wondering how i would check for negative
> > > voltage --crossing pin 7 with what? ground? and my simple anaolg needle
> > > radioshak meter showed +3 volts when i crossed from the battery
> > > to pin 7 on all zx03 chips. [ but i could try swapping Zxo3
> > > chips if they are the likely source] ..i assume
> > > that voices 1-6 correspond to chips numbered z2o3-z703 in the 'X'
> > > place . of
> > > course that places chip Z203 under the output board requiring
> > > unscrewing the
> > > whole main circuitboard.
> >
> > To measure negative voltages with an analog meter, just connect the positive
> > input to the meter to ground somewhere, and use the negative input to probe
> > the op-amp outputs; the negative voltages will show up as positive values on
> > the meter. If you have a digital meter, then it'll have a minus sign.
> >
> > If the chips are socketed, then, yes, swapping them is a good way to find
> > bad chips. It's unlikely to be the capacitors, because leaky capacitors pull
> > the voltage toward ground, not toward the minus rail.
> >
> > --
> >
> > Ciao, Paul D. DeRocco
> > Paul mailto:pderocco@
> >
> well i made a mess now
> i first tried swapping all 5 chips (01.02,03,04,05) in the sample and hold area betwwen the Z2 (voice 1) and Z6 (voice 5)-- no change in the touch sensitivity problem. so i had this great fear that the voices were inverted and maybe voice 1 was actually the Z7 row(actually voice 6)...so i pulled out a chip to see if voice 6 would or wouldnt work-- it didnt sound so i put the chip back having confirmed that it was indeed voice 6... but now voice 6 is all messed up-- it plays only a click on all keys till the c sharp in the 4th octave then itplays a loud tone (but not the patch) then above this i get just a quiet high pitch tone on all notes above. I tried switching ALL chips between voice 5 and 6 but no change -- i seem to have killed voice 6 and still have the problem with voice 1-- any great ideas here??
>

> From: wasteking1
>
> good news---i got my voice 6 to operate normally again ultimately
> by just doing a 'tune all' ... i have NO idea what happenned, but
> im glad its back all i knew was that NO chips were bad . anyhow,
> i still have no idea what controls the touch sensitivity on each
> voice. it does NOT appear to be the 4 socketed chips in the
> sample hold area. but that problem is minimal compared to loosing
> a whole voice.

Now that I look into it, I recall that there is a volume offset calibration
that is stored in CMOS RAM for each channel. Not sure why this should have
gotten corrupted (or why Tune All should affect it), but LOWER FUNCTION,
ADJUSTMENTS, 9 allows it to be adjusted, as described on p108 of the manual.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...