Rhodes Chroma Polaris

Hi folks,

i've got a problem with the master volume slider
it doesn't work when i try to regulate the volume.
but it looks like the physical fader is ok,
the "tune one" works. i did this LF D4 check
and the LED lits when i turn the slider up.
(even though i don't know exactly whta this checks? that there is an amount of 256 volume steps available?)
any ideas for that issue, cause changing the fader seems to
be a bit complicate..?

cheers Harald

> From: karmakater
>
> i've got a problem with the master volume slider
> it doesn't work when i try to regulate the volume.
> but it looks like the physical fader is ok,
> the "tune one" works. i did this LF D4 check
> and the LED lits when i turn the slider up.
> (even though i don't know exactly whta this checks? that
> there is an amount of 256 volume steps available?)
> any ideas for that issue, cause changing the fader seems to
> be a bit complicate..?

When you say Tune One works, are you referring to the auto-tune function, or
to the slider function when the LED is on? If you can turn on the TUNE LED
and get plus-or-minus one semitone of master tuning range with the slider,
then the slider is fine.

If the slider itself still works, the only failure I can imagine which would
leave the volume on at a fixed level is a failure on the output board, such
as a short in transistor Q1. Is the volume at maximum, normal, or soft? Did
the master volume work properly before, or is this a unit you just bought,
and it's never worked for you? Or are you fixing someone else's Polaris?

--

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

Hi Paul,

> From: karmakater
>
> this Polaris is mine, i already changed the panels & this works fine.
> and yea, i can turn on the TUNE LED and get plus-or-minus, so
> i think the slider is fine.
> The volume is always on maximum, i change it now through the
> assignable volume control,
> this works. The master volume didn't work even before i
> changed the panels, i hoped that
> this panel change might fix it.
>
> If the problem is the transistor Q1, is it "easy" to change?
> I got a little experience in soldering.

Yes, it's pretty easy. If you can't find a 2SA1029, any small PNP transistor
should work, like a 2N3906, as long as you figure out which leads are which.
However, since answering you, I realize there are other failures that could
cause the same problem, but they should be easy to check.

First, open the unit up and unplug the three-wire cable that runs from the
output board and plugs into the main board, which has an 8-position
connector at the end. If the volume remains high, then the problem is on the
output board, probably the transistor. If the volume drops to zero, then
there is a problem in the sample-and-hold circuit that drives the master
voltage control line.

This line comes from Z603-8, one of the op-amps in the fifth channel. (The
service manual is available at rhodeschroma.com.) You'd have to remove the
keyboard to get at this, but that's only a few screws. Fortunately, these
parts are socketed, so you could tell if the op-amp is bad by swapping the
part with the analogous part in a different channel, say, Z503. If that
fixes it, you're all done, because that op-amp section isn't used for
anything in the other channels. If not, then it's probably one of the CMOS
switches in the sample-and-hold circuit, which would be either Z601 or Z602.
Again, you could swap those with, say, Z501 and Z502, and if everything
works, you're done. This would mean that only that op-amp in Z603, or that
particular switch channel in Z601 or Z602, had burned out.

Ideally, you would diagnose these things by reading voltages with a meter
while moving the master volume slider. If the above doesn't fix it, then
you'd have to delve deeper and do a real diagnosis. Not every electronic
failure can be solved by swapping a few socketed parts. But you might get
lucky.

--

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

Thanks for the information Paul,
i will check this out these days as far as i can
and hope to be lucky.

cheers Harald

>
> Yes, it's pretty easy. If you can't find a 2SA1029, any small PNP transistor
> should work, like a 2N3906, as long as you figure out which leads are which.
> However, since answering you, I realize there are other failures that could
> cause the same problem, but they should be easy to check.
>
> First, open the unit up and unplug the three-wire cable that runs from the
> output board and plugs into the main board, which has an 8-position
> connector at the end. If the volume remains high, then the problem is on the
> output board, probably the transistor. If the volume drops to zero, then
> there is a problem in the sample-and-hold circuit that drives the master
> voltage control line.
>
> This line comes from Z603-8, one of the op-amps in the fifth channel. (The
> service manual is available at rhodeschroma.com.) You'd have to remove the
> keyboard to get at this, but that's only a few screws. Fortunately, these
> parts are socketed, so you could tell if the op-amp is bad by swapping the
> part with the analogous part in a different channel, say, Z503. If that
> fixes it, you're all done, because that op-amp section isn't used for
> anything in the other channels. If not, then it's probably one of the CMOS
> switches in the sample-and-hold circuit, which would be either Z601 or Z602.
> Again, you could swap those with, say, Z501 and Z502, and if everything
> works, you're done. This would mean that only that op-amp in Z603, or that
> particular switch channel in Z601 or Z602, had burned out.
>
> Ideally, you would diagnose these things by reading voltages with a meter
> while moving the master volume slider. If the above doesn't fix it, then
> you'd have to delve deeper and do a real diagnosis. Not every electronic
> failure can be solved by swapping a few socketed parts. But you might get
> lucky.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>