Rhodes Chroma Polaris

Hi,

I am the owner of Chroma Polaris serial #01576, which has been sitting
idle for many years now in my basement. It has gotten very little use
and cosmetically it looks pristine, but of course with parts like these
membrane switches you can't really tell if they work just by looking.

I had not been aware that these machines had batteries inside, so of
course the first thing I found when I opened it up was that the
batteries (original equipment, apparently: they are Matsushita D cells
labeled in Japanese) had leaked all over the battery compartment. I
took them out and temporarily wired in a partly used 3V lithium cell
from a camera - if I get the machine working, I'll fix up the battery
compartment later. It still wouldn't boot up, so according to the
instructions in the service manual I tried to adjust the resistors on
the power supply. I don't have a scope, just a handheld tester, but I
thought I'd try. First R17 until the LED came on, which allowed the
machine to boot up but not make any sounds. Then R9 to adjust the
voltage across P2-P3 - it started around 4.7, and with R9 turned all
the way I couldn't get it above 4.85V. The spec is 5.00V +/- 0.01.
Does that mean I need a new power supply? Is it possible to still get
parts for these things? I'm willing to tinker a bit.

I'm reluctant to ship this behemoth across the country hoping that it
might be fixable. I saw at rhodeschroma.com a mention of a repair
shop near Boston that doesn't seem to exist any more. Does anyone
have a lead on whether I might be able to find someone local, or at
least near the northern NJ to Boston corridor, who can fix these?

Thanks in advance for any advice.

> From: d_thumim
>
> I am the owner of Chroma Polaris serial #01576, which has
> been sitting idle for many years now in my basement. It has
> gotten very little use and cosmetically it looks pristine,
> but of course with parts like these membrane switches you
> can't really tell if they work just by looking.
>
> I had not been aware that these machines had batteries
> inside, so of course the first thing I found when I opened it
> up was that the batteries (original equipment, apparently:
> they are Matsushita D cells labeled in Japanese) had leaked
> all over the battery compartment. I took them out and
> temporarily wired in a partly used 3V lithium cell from a
> camera - if I get the machine working, I'll fix up the
> battery compartment later. It still wouldn't boot up, so
> according to the instructions in the service manual I tried
> to adjust the resistors on the power supply. I don't have a
> scope, just a handheld tester, but I thought I'd try. First
> R17 until the LED came on, which allowed the machine to boot
> up but not make any sounds. Then R9 to adjust the voltage
> across P2-P3 - it started around 4.7, and with R9 turned all
> the way I couldn't get it above 4.85V. The spec is 5.00V +/-
> 0.01. Does that mean I need a new power supply? Is it
> possible to still get parts for these things? I'm willing to
> tinker a bit.

If it can't get up to 5V, it either means there's something worn out in the
supply, or that something elsewhere is pulling it down. My bet would be the
filter capacitors in the supply are dried out, and that the 5V rail has lots
of 120Hz ripple on it. If you had a scope, you'd be able to see this easily
enough, but you might also be able to to test this by hooking some
headphones across the 5V through a small capacitor (maybe 1uf to 10uf) to
block the DC. The rail should be quiet, but you'll hear a nasty hum if
there's ripple on it.

It might not be a bad idea just to replace all the large filter caps, even
if you have to hand-wire caps of a different physical form factor. They're
notorious for drying out. It's doubtful that any impossible-to-get part
(like the power transformer) is bad; the rest of the supply is just
garden-variety stuff you can get from places like DigiKey.

Since your memory contains nothing but garbage, you should also do the steps
on page 6-5 of the service manual. You may find this brings things back to
life--that is, if the membrane switches will let you.

--

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

> From: Brinkmann Music
>
> Hope somebody can help me with this. Powered up today and
> noticed that the polaris is out of tune with itself-
> especially upper two octaves. Seems to be every 3 or 4 half
> steps that are out of whack. Otherwise, o.k.
>
> Left it powered on for hour or so- nope.
> Autotune all voices- nope. And all voices are tuning and
> play- so I haven't lost a voice. Tune individual channels-
> after several attempts- sometimes worked, mostly made it
> worse- bumped it too high or too low- the beating got faster
> or slower- but still hear beats.
>
> Last resort- full reset (I know probably an issue that calls
> for replacing components inside, but I'm lazy- and not good
> with a soldering iron). Nope. Well, at least now I can see
> if Soundiver still works and can load back my patches... and
> play them out of tune. . .
>
> So, what can be done to get it back in tune?

That generally means that one channel has some leakage current pulling the
pitch control voltage around. There is a function in the manual that you can
use to disable the bad channel, in a pinch, leaving you with the good five.
Otherwise, you'll just have to get it fixed. It's probably a leaky cap or
CMOS switch in the sample-and-hold, but could also be in the oscillator
circuit itself.

--

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

I did notice that SYNC stopped the "beats" on each individual note- the note
was in tune. But, the entire keyboard was still NOT in tune with itself.

Let me know if replacing the sample-and-hold caps solves the problem.

Thanks

-----Original Message-----
From: chromapolaris@yahoogroups.com [mailto:chromapolaris@yahoogroups.com]On
Behalf Of STEVEN PISTRICH
Sent: Monday, September 03, 2007 6:51 PM
To: chromapolaris@yahoogroups.com
Subject: Re: [chromapolaris] Out of Tune


Funny, I was almost ready to write in with virtually your same exact
question....but I had the same problem 4 months ago , but right before i
took it apart I seemed to temporarily solve it with the "retune procedure''
in the manual. Now the detune is back but a little different and the
retuning wont solve it, (sometimes the SYNC button realigns the oscilators
on some sounds) .. the answer I believe has to be surgery.

I must finally replace the orange Sample-and-Hold capacitors that keep the
sounds 'stable' . they are very visible on the motherboard ,They dont cost
a lot and are available through Digikey. All the info about this surgery
is posted on this polaris site if you research further back. I was
reluctant to dive in with the soldering iron, but others have written in
that it is the only answer to the 'odd detuning' problem, Im trying to get
psyched up to do it now. at least you dont have to touch those ribbon
wires.

Paul D. DeRocco wrote:

> > From: d_thumim
> > ...adjust the resistors on the power supply. I don't have a
> > scope, just a handheld tester, but I thought I'd try. First
> > R17 until the LED came on, which allowed the machine to boot
> > up but not make any sounds. Then R9 to adjust the voltage
> > across P2-P3 - it started around 4.7, and with R9 turned all
> > the way I couldn't get it above 4.85V. The spec is 5.00V +/-
> > 0.01. Does that mean I need a new power supply? Is it
> > possible to still get parts for these things? I'm willing to
> > tinker a bit.
>
> If it can't get up to 5V, it either means there's something worn out in the
> supply, or that something elsewhere is pulling it down. My bet would be the
> filter capacitors in the supply are dried out, and that the 5V rail has lots
> of 120Hz ripple on it. If you had a scope, you'd be able to see this easily
> enough, but you might also be able to to test this by hooking some
> headphones across the 5V through a small capacitor (maybe 1uf to 10uf) to
> block the DC. The rail should be quiet, but you'll hear a nasty hum if
> there's ripple on it.
>
> It might not be a bad idea just to replace all the large filter caps, even
> if you have to hand-wire caps of a different physical form factor. They're
> notorious for drying out. It's doubtful that any impossible-to-get part
> (like the power transformer) is bad; the rest of the supply is just
> garden-variety stuff you can get from places like DigiKey.

Actually, the transformer itself does look a bit rusty... what is so
unique about this one that it can't be replaced?

> Since your memory contains nothing but garbage, you should also do the steps
> on page 6-5 of the service manual. You may find this brings things back to
> life--that is, if the membrane switches will let you.

Most of the membrane switches do seem to work, but alas STOP is not
among them which prevents me from getting past step 1. *sigh*
Replacing those switches looks like a major headache. This is
starting to look more like a long term project than a little
tinkering.

Thanks for your help.

-- |)aniel

> From: Daniel Thumim
>
> Actually, the transformer itself does look a bit rusty...
> what is so unique about this one that it can't be replaced?

All transformers are "unique" in that there isn't a simple list of standard
transformers that everyone uses, like resistors. You could certainly find a
substitute that would work okay (although I doubt you need one), but I doubt
it would have the same mounting hole spacing, or be exactly the same rating.
The other parts, including the ICs, are things you can easily get exact
replacements for.

> Most of the membrane switches do seem to work, but alas STOP
> is not among them which prevents me from getting past step 1.
> *sigh* Replacing those switches looks like a major headache.
> This is starting to look more like a long term project than a
> little tinkering.

Yup. I wish someone with access to silkscreening equipment would make some
replacement membrane switches. A lot of people around here seem to need
them.

--

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

I disabled channels 3,4 and 5. Then was able to play 3 notes at a time in
tune. Sometimes I get a quick "portamento" when playing the bad channels-
scoops up in pitch on first playing.


********

That generally means that one channel has some leakage current pulling the
pitch control voltage around. There is a function in the manual that you can
use to disable the bad channel, in a pinch, leaving you with the good five.
Otherwise, you'll just have to get it fixed. It's probably a leaky cap or
CMOS switch in the sample-and-hold, but could also be in the oscillator
circuit itself.

--

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

*************

> From: Brinkmann Music
>
> I disabled channels 3,4 and 5. Then was able to play 3 notes
> at a time in tune. Sometimes I get a quick "portamento" when
> playing the bad channels- scoops up in pitch on first playing.

That sounds like problems in the sample-and-hold circuits. It's not a really
hard fix, but it does involve taking the board out (which disconnects the
battery and loses the memory), desoldering and replacing a bunch of parts.
I'd start with the pitch-related caps (Cx00, Cx01, Cx04, Cx05), then perhaps
the two 4051 switches (Zx01 and Zx02) on the affected channels. A scope
would make it easier to tell exactly what's bad, so you wouldn't have to
waste time changing things that aren't broken.

--

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

Search the posts on this one.
I had the exact same problem a year or two ago. You can change the
capacitors from the top of the board if your are carefull. You add
extra solder to help remove w/o damaging the traces, and then insert
replacements from the top.

-Ben

Today, it is other channels that stay in tune, so that seems to change. I
have a manual, I assume the schematics are on the chroma webpage somewhere.
Maybe I'll be brave and try, but I don't have a scope. I also don't have a
desolder bulb thing, don't I need one? Thanks.

> From: Brinkmann Music
>
> I disabled channels 3,4 and 5. Then was able to play 3 notes
> at a time in tune. Sometimes I get a quick "portamento" when
> playing the bad channels- scoops up in pitch on first playing.

That sounds like problems in the sample-and-hold circuits. It's not a really
hard fix, but it does involve taking the board out (which disconnects the
battery and loses the memory), desoldering and replacing a bunch of parts.
I'd start with the pitch-related caps (Cx00, Cx01, Cx04, Cx05), then perhaps
the two 4051 switches (Zx01 and Zx02) on the affected channels. A scope
would make it easier to tell exactly what's bad, so you wouldn't have to
waste time changing things that aren't broken.

--

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

> From: Brinkmann Music
>
> Today, it is other channels that stay in tune, so that seems
> to change. I have a manual, I assume the schematics are on
> the chroma webpage somewhere. Maybe I'll be brave and try,
> but I don't have a scope. I also don't have a desolder bulb
> thing, don't I need one? Thanks.

It would help, and they're not expensive. I prefer the spring-loaded-plunger
type solder sucker. Fortunately, it's an ancient board with giant thru-hole
parts, unlike today's surface mounted specks.

--

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

> From: Chris Ryan
>
> Sorry for the delayed response. I had an e-mail exchange with
> Richard Lawson of RL Music (rlmusic.co.uk) a couple of months
> ago about the possibility of making replacement membranes for
> the Chroma. He wrote, "The Membrane manufacturing is going to
> be too expensive it seems after discussing this with my tech.
> The design of the micro-switches into the membrane itself
> means this is a complex manufacturing process that would
> require specialist tooling. Having some experience with
> restoration work, I know without even a detailed
> investigation that this is not going to be cost effective
> unless we were to sell hundreds of them and I doubt that is
> ever going to happen." I'm not sure how similar the Polaris
> membrane mechanism is to the original Chroma.

Well, they work on the same principle, but that's about the only similarity.
The reason the Polaris ones fail and the Chroma ones don't is that Fender
Japan decided to make the Polaris ones out of something other than plain
Mylar, for reasons that are as lost in the mists of history as the tooling
they used to make them. (On the other hand, has anyone actually tried to
contact FJ to see if someone there has the tooling sitting in a dusty
closet?)

Without the original tooling, the actual screen printing would probably be
fairly cheap, but the expensive part would be the knife-edged dies that cut
all the holes in each piece. In such small quantities, it would probably be
easier to make a few individual punches, and then punch all the holes by
hand. In addition to the single size of LED hole and slider slot, the
switches themselves need a dime-sized hole in the spacer layer, so that
makes three small punches that would have to be fabricated. The outline,
including the tails, could probably be cut with scissors. Not fun, but not
impossible.

Given the passion some users have for their Polarises, it wouldn't surprise
me if some people would be willing to cut all the holes and slots by hand
for their own instrument, using an X-acto knife.

--

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

Yes it would be expensive for sure!
The large size of the Polaris panels would mean extra expense since
area strongly drives costs for board/flex manufacturing. In general
flex is 1.5x the tooling charge of a rigid PCB.

For now, manual panel drilling and replacement is far more economical
(~2.5hrs labor and $70 in switches). With a hot tweezer, I was able
to speed up the process. I don't have access to a $2000 wire
cutting/stripping machine, but with one it could be even faster.

-Ben