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ChromaTalk Archives: September 2000

advice on Chroma problem sought

Michael Frishkopf


I purchased a used Rhodes Chroma around 1985, and used it extensively until 1989 when I put it in storage while travelling and living elsewhere. Finally, this year I had my stored possessions shipped to me, including the Chroma. Unfortunately, it no longer plays. When I first turned it on it produced a continuous sound (without any key having been pressed) while the program number lights flickered slightly. At this point it was possible to press various buttons and hear the tapper functioning.

When I turned it off and on again, the Program Number lights did not illuminate, the Data Readout displayed the single letter "P", and it was not possible to change anything by pressing any buttons, although some of the panel LEDs were on. Nor did the tapper function.

I remembered that there are AA batteries inside, opened it up, and changed them. The old ones had leaked a bit, but not badly. When I turned it on again, I obtained the same result as before: no sound, Program Number blank, Data readout = "P", can't change anything by pressing buttons. [Can anyone confirm the correct orientation of these AA batteries in the holder?]

While in storage the instrument was not subjected to temperature extremes, though the temperature might have fallen into the 50s. I did notice that the foam liner to the Anvil case has lost its resiliency, and stuck to the wood, though it doesn't seem to have gotten inside the unit.

Can anyone suggest what might be wrong, and how it could be fixed?

Many thanks for any advice.

with best regards,

Michael Frishkopf
Department of Music
Faculty of Arts
University of Alberta

Don Tillman

Well, you have evidence that *parts* of the Chroma are working.

I would recommend...

First mechanical: A thorough cleaning and vacuuming, cleaning and checking all the contacts and connectors, reseating all the boards, making sure there's no corrsion, dust or anything like that.

Then the power supply voltages: If the +5 volt digital supply is off you'll get pretty useless behavior, like what you've described. Adjust this with an accurate meter so it's exactly 5.00 volts. Actually the manual recommends 5.05 volts. But if you're hovering around 4.6 volts things will be bad.

David Clarke [21030085++]

I'll 2nd Don Tillman's recommendations.

Further, if you get to the point that the 5v power rail is OK but the Chroma is still being cranky, then I'd first double check that there was no battery/acid damage to the traces on the CPU PCB and/or to the components nearby the battery holder.

If that looks OK, then my attention would go to the reset circuitry (i.e., the signal that tells the main processor that the power is OK and that it should start running code).

You had also asked for someone to "...confirm the correct orientation of these AA batteries in the holder?..."

If you're looking at the chroma from the front (i.e., keys in front of you, power supply to the back) and with the panel flipped up (so you can see the batteries) they'd go in like this (please forgive the poor ASCII drawing :-> )


     -      -----
+  _|_|_    |   |  -
   |   |    |   |
   |   |    |   |
   |   |    |   |
   |   |    |   |
   |   |    |___|
   |   |     | |
-  -----      -    +

You can always double check to see if everything is OK by placing a voltmeter across the battery-backed RAM chips (with the power off). If you see +3V or so, then you've got the batteries in correctly.

(BTW, you can run the Chroma successfully without batteries installed, other than the fact that the Chroma will forget its patches every time it is turned off.)



Windows/Chroma interface

Mark R. David [21030170+]

I've completed my initial chunk of design work on my Windows/Chroma interface project. Rather than bore you all with the details here, I've put it up on the Web at: [URL removed, as the site is now gone].

See Windows Editors & Librarians: Windows Interface for Chroma for links to related threads.

Comments are solicited, especially because I am trodding in territory very unfamiliar to me here.

I've refrained from putting a mailto link on the site which sends to the entire list, because I don't know the protocol on this list. I have no plans to advertise the existence of this stuff outside this list. It would be easy enough to add one; let me know whether I should/shouldn't.

Thanks, Mark David

Mark R. David

Windows/Chroma interface circuit design - first pass completed.

I've posted here my first pass at the circuit design: [outdated URL removed]

In case the warnings there aren't big and red enough, I haven't prototyped or debugged this circuit yet, so I wouldn't recommend building it yet. I'll send another message when the circuit is final, and I begin working on the Windows Server Object Library.

Till then, all comments and criticisms are solicited and welcome.

Mark David

Broken Chroma

Werner Schöenenberger [21010114]

Hi list,

I just joined this tech-list due to a problem, I have with a Chroma. Currently I have a Chroma from a friend of mine in my home and was asked by my friend to repair it. I downloaded the schematics and I am ready to go. Since I never had to do a lot with the Chroma before, I kindly ask you to give me some hints that might help to solve the problem the Chroma has.

When turning the chroma up, ALL voice boards are disabled. I basically checked the voltages, everything is ok. The panel also works 100%. I think it must be a small fault because it affects all of the eight voice cards.

If you can give me some hints how to start with searching for the solution of the problem, this would be VERY helpful.

THANK YOU YERY MUCH and best wishes

Werner Schönenberger

David Clarke [21030085++]

Here are a few things you could try:

Remove all 8 voice cards.

  1. Looks to see if any of the cards might have one or more of the connectors on the bottom 'folded back' so that the pins do not get inserted correctly.
  2. Ensure that that none of the pins (which mate with the voice boards) are bent such that they are touching one another
  3. Take one of the eight cards and reinsert it. Power on the keyboard and see if 7 or 8 boards have failed.
    1. If it reports only 7 failed boards, then successively power down the keyboard, add more boards and confirm that each passes the auto-tune properly.
    2. If it still reports that 8 boards have failed, then confirm the cables going to the channel motherboard are correctly connected.

If you're not lucky enough to get things working with the steps above, then the next place I'd start to look is with the power supply rails - making sure that +12, -12 and +5 are all within spec - both at the power supply and on the channel mother board.

Christopher Now


It's possible that _all_ your voices are out of calibration, especially if the unit was stored for a long time, or you had an "event" that necessitated a repair and/or resetting of voltages in the supply. You may have already tried, but by doing a set-split 31, you'll re-enable (unmute) the voices. If they are simply all out of calibration, you'll be able to quickly hear this when you play some notes. If this is the case, the voice calibration procedure in the manual is fairly straight forward.

Otherwise, check voltages on the channel mother board.

Good luck

Werner Schöenenberger [21010114]

Hallo David,

THANK YOU VERY MUCH for your hints. I will test it out and send some feedback.