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Chroma Polaris Boot issue - please help!

2018-11-16 by sonicalliance@...

Hello everyone! My name is Jon, my friends call me Fetz.

I was recently gifted one of the beautiful Chroma Polaris synths.

I am having an issue with the synth and I needed some help. When I turn it on, all of the LEDs on the front panel are lit. No sound when I press keys, buttons do not respond. I tried turning it off, waiting and turning it back on. This worked twice over various on/off attempts. When I was getting sound out of it, all sliders worked. I was able to change patches and modify some parameters. Some membrane buttons didn't work, but most did.

My question, is the membrane related to the boot issue? Will a new membrane install solve it? Or is that a separate issue? I have been searching through the manuals for some type of reset function to see if that will fix the problem. I learned about the Warm Reset and Reset functions, but I can't seem to use them while the synth is in the error state.

Any help, tips and feedback are greatly appreciated. The two times I was able to play it have left me in love with the Polaris. Thank you continuing support of this beautiful synth. Your time and help is greatly appreciated.

Best regards,
Fetz

RE: [chromapolaris] Chroma Polaris Boot issue - please help!

2018-11-26 by Paul D. DeRocco

> From: sonicalliance@...
>
> I am having an issue with the synth and I needed some help.
> When I turn it on, all of the LEDs on the front panel are
> lit. No sound when I press keys, buttons do not respond. I
> tried turning it off, waiting and turning it back on. This
> worked twice over various on/off attempts. When I was getting
> sound out of it, all sliders worked. I was able to change
> patches and modify some parameters. Some membrane buttons
> didn't work, but most did.
>
> My question, is the membrane related to the boot issue? Will
> a new membrane install solve it? Or is that a separate issue?
> I have been searching through the manuals for some type of
> reset function to see if that will fix the problem. I learned
> about the Warm Reset and Reset functions, but I can't seem to
> use them while the synth is in the error state.

When the system doesn't respond at all, it means the computer isn't running at all, or has crashed. There are two common causes of this in old Polarises:

1) You have the old version of the power supply, which holds the processor in the reset state until the voltage is above an adjustable threshold, and that adjustment has gone out of whack after a long time. This power supply has a red LED that turns on when the reset signal goes off, so it's easy to see if this is causing the problem, and trivial to fix: you just twist the nearby trimmer (R17) to find the point where the LED turns on or off, and go past that by about 10 or 20 degrees so that it is safely on.

2) The EPROMs holding the software have faded, and occasionally a bit is read incorrectly, crashing the computer. It's hard to know when this is a problem, but you could tweak the +5V supply both upward and downward with power supply trimmer R9 (old board) or R4 (new board without LED) to see if it changes anything. (On the old board, you'd have to readjust R17 to make sure the LED still comes on.) It's best to do this while monitoring the voltage with a meter, to stay within 4.5V to 5.5V. This may not reveal anything, but if some bits are on the "hairy edge", they may be sensitive to supply voltage.

If this is indeed the problem, the solution is simply to erase and reprogram the EPROMs, and then go through the whole initialization and calibration process described in the service manual. The code and all manuals are available on the rhodeschroma.com site (use the latest version). If you don't have a programmer, and can't find anyone who can do it for you, you could buy an eraser and programmer on eBay and do it yourself. For about $50, you can get a Willem programmer on a circuit board without a box, and an eraser, or get a GQ programmer in a nice package for about $100.

Of course, beyond that, there are any number of other things that could cause the problem, which would be more difficult to diagnose, except by someone with some real electronic experience and a decent scope, but those two are the first things to look at.

--

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

RE: [chromapolaris] Chroma Polaris Boot issue - please help!

2018-12-15 by sonicalliance@...

Hello Paul,

Thank you very much for this feedback. I have some work to do on this beauty! I have been swamped in holiday season as work. I have a good friend who is technically inclined and I'm going to see if he can help. I will investigate and report back with update or any questions.

Thanks again for your help!

Happy Holidays!

Fetz

Re: Chroma Polaris Boot issue - please help!

2019-01-20 by sonicalliance@...

Hello Paul - Happy New Year!

I was finally able to work on the Polaris with my computer engineering friend. We were able to solve the power reset issue. We tweaked the R17 trimmer until the red LED went on. It now turns on and off properly, and plays. We also successfully replaced the membrane panels. They function normally.

While we were inside, we replaced the D batteries, which were still holding 3.0 volts.

Unfortunately we now have a new problem to solve. Every note is out of tune - one quart to one half step sharp. The sound of the oscillators appears to be wavering. We attempted the Tune All function, which completed but did not change or fix the tuning.

We read in the manual that you can disable the oscillators by setting them to Pulse with the width at 0%. When both oscillators are set this way, the keyboard makes sound. Is that the expected behavior? We tried isolating the issue to the oscillators but we don't understand what the proper behavior is.

We tried isolating the 6 voice channels, but all channels played exactly the same, too sharp. They all wavered and were out of tune.

Using the Pitch Bend lever, we could force it into tune while holding the lever in place.

We found an article online of an Australian Polaris owner who had the same issue. He had to replace all the tuning caps on Channel 1 (C102-C108). Do you think this could be the same problem? If not, how could we debug this? We have an oscilloscope and multimeter and schematics.

The original capacitors are polypropylene and my engineer friend doesn't know what that is. Can we just use ceramic caps?

Any advice you can offer is greatly appreciated.

Thank you for all your time and help. We are excited by the progress we have made, and can't wait to make music with this synth.

Best regards,

Fetz

RE: [chromapolaris] Re: Chroma Polaris Boot issue - please help!

2019-01-21 by Paul D. DeRocco

> From: chromapolaris@yahoogroups.com
>
> Unfortunately we now have a new problem to solve. Every note
> is out of tune - one quart to one half step sharp. The sound
> of the oscillators appears to be wavering. We attempted the
> Tune All function, which completed but did not change or fix
> the tuning.
>
> We read in the manual that you can disable the oscillators by
> setting them to Pulse with the width at 0%. When both
> oscillators are set this way, the keyboard makes sound. Is
> that the expected behavior? We tried isolating the issue to
> the oscillators but we don't understand what the proper behavior is.
>
> We tried isolating the 6 voice channels, but all channels
> played exactly the same, too sharp. They all wavered and were
> out of tune.
>
> Using the Pitch Bend lever, we could force it into tune while
> holding the lever in place.

If the oscillators are all over the place, it may be a problem with the DAC, or with a power supply, in which case the pulse widths would be all over the place too, so setting them to 0 won't necessarily shut them up.

> We found an article online of an Australian Polaris owner who
> had the same issue. He had to replace all the tuning caps on
> Channel 1 (C102-C108). Do you think this could be the same
> problem? If not, how could we debug this? We have an
> oscilloscope and multimeter and schematics.

> The original capacitors are polypropylene and my engineer
> friend doesn't know what that is. Can we just use ceramic caps?

Most ceramic caps have high ESR. The polypropylene have low ESR, and low leakage. Those are the two important characteristics. But I doubt that's the problem, because that would result in only minor tuning issues.

Since you have a scope, you should make sure the power supplies are clean (no 120Hz ripple). And you should look at the control voltages to the oscillators on the sample-and-hold op-amps and see if they're moving around in synchronization with the wavering pitch.

If the pitch is stable, but way off, then it could also be a problem measuring the frequency during auto-tune. But "wavering" sounds like something power supply related.

--

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

Re: [chromapolaris] Re: Chroma Polaris Boot issue - please help!

2019-01-21 by David Clarke

> … Unfortunately we now have a new problem to solve. Every note is out of tune -
> one quart to one half step sharp. The sound of the oscillators appears to be wavering.
> We attempted the Tune All function, which completed but did not change or fix the tuning...
> Using the Pitch Bend lever, we could force it into tune while holding the lever in place...

Further to Paul's recent note (and just to clarify) - is it confirmed that the behaviour occurs on all voice patches and is also seen when using a 'scratch patch'? [e.g., just to rule out the simple case where the currently selected patch is actually programmed to modulate the frequency/shift the tuning)]

David Clarke

Re: Chroma Polaris Boot issue - please help!

2019-01-22 by btmckee9@...

Hi. I'm Fetz's EE friend, Brian. We were able to reproduce the quaver issue with the scratch pad.

I suspect the issue is power related based on what Paul suggested. It makes sense that calibration wouldn't work if there was noise on the power supply.

In fact, one time we calibrated, it seemed to be in key. I thought it was just a fluke since we tried again and again after that and it was off by a similar amount to the previous times. We just happened to calibrate it when the power oscillation was in the right phase.

When we had it apart I noticed that the whole system is powered by a giant AC transformer running into two full wave rectifying diodes which then feed linear regulators bolted to a giant heat sink. Gotta love that 1980's tech.

My guess is, since power measured okay with a meter, that the electrolytic caps in the power supply have gone bad. Since they are 30 years old, I'm not surprised. Are there other caps we should check?

Thanks much for the help. It was great fun to see that old synth come back to life.

Brian