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ChromaTalk Archives: May 2003

A-Z of Analogue Synthesizers (Revised)

Chris Ryan [21030691] · Sat, 3 May 2003 00:29:03 -0700

Peter Forrest has just published a revised edition of his book, "The A-Z of Analogue Synthesizers--Part Two: N-Z." [See the Bibliography for more information.] The Chroma/Expander section is completely revised and expanded, thanks in part to feedback from me and David Clarke (both of us are thanked in the book) and the site in general, which gets several mentions. I've posted the revision: see A-Z of Analogue: Rhodes.

There is tonnes of information in the book, and I'm going to order the A-M volume. I think they're must-haves for any analogue enthusiast.

Doug Terrebonne [21030114] · Sat, 3 May 2003 01:11:11 -0700 (PDT)

They are great books... The Chroma Polaris is listed in the A-M volume. It erroneously states the Polaris II was only planned and not released. I emailed Peter telling him that's incorrect and that I actually have one... I still don't know what the difference to the original really is other than the graphics, however...

Chris Ryan [21030691] · Sat, 3 May 2003 12:35:07 -0700

I'm still not sure exactly what a "Polaris II" is; my understanding (I believe from talking with Tony Williams) was that the models with red and yellow switches were prototypes and were never commercially available; and the blue ones were the production units. Were there other revisions?

David Clarke [21030085++] · Sat, 03 May 2003 20:29:51 -0400

Polaris Rev's

Insofar as I know, all production/commerical units are black with light/dark blue graphics.

The Polaris II is a bit of a mystery. For all intents and purposes it seems to be the same as the original Polaris (i.e., generally looks the same, and seems to have the same specs) BUT it does have a slight modification to the graphics to indicate "II."

I had my Polaris quite a long time before my Chroma and I've always been curious about the Polaris II (so much so that I seriously considered buying a II, just to see if I could tell what the real differences were).

There was a Polaris II for sale on Ebay a while ago (with a pic. showing the different graphic), but I can't seem to see it come up in a 'completed items' search there.

Doug - did you receive any different manuals with the II (that specifically say 'II' on them)?

Doug Terrebonne [21030114] · Sat, 3 May 2003 18:32:56 -0700 (PDT)

Re: Polaris Rev's

I have taken a couple pics of my Polarii (I and II):

Obsolete URLs removed; here are the pictures.

The only diffs on the II that I can tell are the lack of red and blue in the Chroma logo (just plain white), the "II" label, and the handy Lower Functions chart on the front. The SN plate says the II is Model 2123B and is a Japanese 100V unit so perhaps they were only sold in Japan (both are made there). Also interesting is that my II has an older ROM than the I.

Corley Brigman [21030386] · Sun, 4 May 2003 10:41:37 -0700

Re: Polaris Rev's

dunno if this has been mentioned, but in the service manual, the power supply has 'early version' and 'late version' pages. nothing else changes.

i can't see them calling it a 'II' based on this, but maybe that's all that's different?

David Clarke [21030085++] · Sun, 04 May 2003 16:47:25 -0400

This could have been part of the thinking - but I have seen non-II Polaris'/Polarii with both the old and new power supplies.

There are other (potential) differences noted in the service manual - such as a slightly faster CPU, more RAM and more EPROM/code space. Maybe a II ended up being a 'fully expanded I'?

David Gowin [21030611] · Mon, 05 May 2003 09:21:55 -0400

Sorry, but how were the graphics different on the Polaris II? I know there was a project for a Polaris Expander and there were some CPU Upgrades but never heard of the Polaris II though!

Thx!

David Gowin [21030611] · Mon, 05 May 2003 09:26:03 -0400

Good morning. I was lucky enough to have the blessing and support of Fender to run the Chroma Poalris Users Group. While there were plans to build a Polaris Expander and there was at least one CPU upgrade during production, never heard of a Polaris II! Would be interesting to see if it's the Halloween Polaris (like the Halloween Chroma) or a true revision/update.

Chris Ryan [21030691] · Mon, 5 May 2003 08:23:23 -0700

On Monday, May 5, 2003, at 06:21 AM, David Gowin wrote:

Sorry, but how were the graphics different on the Polaris II?

See Doug's pictures, sent to the list a couple of days ago.

Woodwork on a Prophet T-8

David Clarke [21030085++] · Sat, 03 May 2003 20:47:02 -0400

I've never seen one up close - but from the pictures I've seen, the layout of the woodwork on a Prophet T-8 seems to be nearly identical to the Chroma (single piece end-cheek, strip of wood along the front under the keys, another at the front of the top panel, etc.).

Is there anyone on the list that has seen both, and can comment on how close they really are (or aren't)?

Jack Colburne [21030142+] · Sun, 4 May 2003 01:14:57 -0400 (EDT)

Not sure what kind of feedback you're looking for but, in my old age, I remember the T8 being quite a bit thinner than the Chroma. Maybe 4-4.5 inches to the Chroma's about 6 inches. I also remember it being a little less deep than the Chroma. (One of those keyboardist "Remembering carrying one and putting it on the stand by yourself" memories). Not sure about the color, but I remember the Prophets as being a lighter brown stain than the Chroma sort-of-darkcherry. Could be wrong. The T8 was longer than the Chroma (more keys) so the front pieces would have been longer. The end panels were also shaped a bit differently. I thought they helped make the thinner T8 look even more sleek.

Murray Macdonald [21030276+] · Sat, 3 May 2003 23:15:29 -0700

I can help here. I have two Chromas, Two Polarii and two T-8s. The T-8 is much thinner and has a longer keyboard. Like the chroma, the T-8 has an angled panel, and a flat top. The T-8 is covered in knobs. Every parameter is immediately accessible. The T-8 is an incredible synth. Buy one, or two. I'll take some quick pictures and post them early next week.

Csaba Zvekan [21030495] · Sun, 4 May 2003 10:48:50 +0200

RE: Chroma: Woodwork on a Prophet T-8I was wondering how many Chromas were made ? And while were at it how many Chroma Polaris /Polaris II and Prophet T8s.

It is true the T8 is lighter in color and the woodwork is much thinner. Also the way they treated the on the chroma seems not quite the same.It changes over time. The varnish I mean !

Chris Ryan [21030691] · Sun, 4 May 2003 10:04:11 -0700

I was wondering how many Chromas were made ?

There have been a couple of discussions on this topic previously on the mailing list:

Also, Peter Forrest addresses the issue in his revised version of "A-Z of Analogue [Rhodes]," which I posted a couple of days ago.

The general consensus seems to be that the number is significantly lower than Philips Dodds' estimate of 3000 in the "Synth That Survived ARP's Fall" article.

Murray Macdonald [21030276+] · Wed, 7 May 2003 22:13:32 -0700

Hi ,

For those of you interested in the size of the T8 vs the Chroma, I have taken a few quick and dirty T-8, Polaris and Chroma pictures to provide a quick visual reference. Due to file size limitations an 11 picture collection of full-sized images (500K-700K per image) is available online at http://macdonald.tv/t8 [archive.org]

Here's one of the pictures comparing the Polaris to the T8.

Enjoy,

--Murray

Mirko Lüthge [21010245+] · Sat, 17 May 2003 15:00:20 +0200

Hi,

I am owner of a Chroma [21010245] + expander [16330046], and also of a T-8, Pro 10, Pro 5. I like them all. Buy them if possible. I have another Chroma which has to be repaired. After repairing I will sell it. [Obsolete URL removed.]

greetings Mirko - ex-Synthesizer-Cooperation

David Clarke [21030085++] · Sat, 17 May 2003 18:09:15 -0400

Hello Mirko - I can see the Chroma & Expander on the registry list - but not the second Chroma. If you have the details for it, it would be nice to also have it in the registry.

Error Messages/ Power Supply

Csaba Zvekan [21030495] · Tue, 6 May 2003 09:34:59 +0200

HI Everybody,

I'm trying to get my Chroma up and running. So far I have replaced the 10uF, 4.7uF and will Replace the 1000uF in the Power Supply. The Voltages seem fine . But still it only boots up properly 1 time out of 20 maybe. Then giving me the Error codes:

Errr 0123, Errr 013 most of the time, Errr 01 had that a few time and lately even Errr 014. I have downloaded the Service Manual but don't seem to find a list with the Error Codes. I understand this has to do with the Voice Cards Failing. I will replace the LM358 OPAMPS and all the CMOS 4016,4013,4071 and might as well replace the 4175/4174 plus the capacitors on that board.

What do you guys think of replacing the whole Power Supply with a self made 7812,7912,7805 based power supply. I ve done that for my ARP 2600 and never had problems again. People were saying it is noisy... but it isn't. Or at least I can't hear any noise.

Any Feedback would be appreciated

David Clarke [21030085++] · Wed, 07 May 2003 21:32:12 -0400

... Errr 0123, Errr 013 most of the time, Errr 01 had that a few time and lately even Errr 014. I have downloaded the Service Manual but don't seem to find a list with the Error Codes.

It is best not to think of the numbers as actual error codes; rather, they're board numbers. So Errr 0123 means voice cards 0, 1, 2 and 3 failed.

Similarly, Err 014 means that voice cards 0, 1 and 4 failed.

When I say 'fail' I really mean that the boards failed the auto-tune routine. This could be due to a faulty component on the voice board, on the channel mother board, on the I/O board, bad settings on the voice boards, a DAC out of whack - or back power supply voltages (among other things).

What do you guys think of replacing the whole Power Supply with a self made 7812,7912,7805 based power supply. I ve done that for my ARP 2600 and never had problems again.

I'm not sure of the design you might have in mind - but the Chroma will want to draw 2.5+ amps on the 5V rail, so it might be tough to do this with a straight 7805.

I certainly won't dissuade you from swapping out the Chroma's power supply - but I would recommend that you convince yourself as the source of the problems prior to going that route (i.e., you might find that the power supply is perfectly OK - but some other component is causing the problem). Troubleshooting failed voice cards is really not that bad, assuming you have a set of schematics and a 'scope/multimeter.

Luca Sasdelli [21010226] · Thu, 8 May 2003 09:02:39 +0200

I'm not sure of the design you might have in mind - but the Chroma will want to draw 2.5+ amps on the 5V rail, so it might be tough to do this with a straight 7805.

Moreover, the Chroma power supply features a +5V for digital logic and a separate a +5V for analog electronics, and a /RESET line is provided by the PSU in order to preserve non-volatile RAM from being corrupted at power-up transition. It's a quite critical item, indeed.

Therefore, I agree with David recommendations to investigate in the voice boards themselves; the first step is to annotate the failed board numbers, and then to swap boards from 0 to 3 with boards from 4 to 7, and see if the error code changes accordingly.

If it does, try to check the test point waveform on the failed voice boards, that should exhibit a 50% duty cycle, by adjusting the respective trimmer on top of the board; alternately, you can connect a headphone to the waveform output on the board itself, and adjust the relevant trimmer in order to obtain the sound as "hollow" as possible, i.e. with the less apparent amount of harmonics.

In order to re-test the boards after an adjustment, press [SET SPLIT] [50] in order to reset the logic.

A channel mother board contact cleaning, during the board swap process, is highly recommended.

Csaba Zvekan [21030495] · Thu, 8 May 2003 09:05:08 +0200

Thanks David,

I meant to say that if it boots up it shows theese Error Messages. But most the time it just stays there with all the leds lit on no Patch number or message displayed. I replaced all the capacitors in the PS. Still don wanna boot up. Pretty frustrating so far !

Csaba Zvekan [21030495] · Thu, 8 May 2003 09:31:25 +0200

O.K

You guys got me convinced regarding the PS with the 79xx,79xx -If I have to I go for the Pro One MAP-80-4000 as described by Donald Tillman. I did pull one Voice Board after another ending up with no board to see if the voice boards create the problem .Still all Leds are on but no funcions are possible. Maybe I didn't express myself right. If it boots up it happend twice in a week then I get the error messages other than that the leds are on and that it no display no sound.

David Clarke [21030085++] · Thu, 8 May 2003 07:33:52 US/Eastern

Maybe I didn't express myself right. If it boots up it happend twice in a week then I get the error messages other than that the leds are on and that it no display no sound.

When the Chroma fails to boot (and leaves the LEDS on), do all the LEDs come on - or just some of them (in a more or less random pattern)?

Here are some general troubleshooting ideas:

Power up the Chroma. Leave it powered in the state where the LEDS are on. While in this state, measure the voltages seen on the individual boards themselves (i.e., CPU board, I/O board, channel mother board). If one or more of the voltages look bad, try tracing back to the PSU to see where it became bad. If the voltage looks bad at the PSU and on a board, disconnect the power connector to that board, and see if the power rail then recovers.

Assuming the voltages all look good, take a look at the RESET signal seen on the CPU board (the signal that comes from the PSU). (i.e., confirm that the CPU does come out of reset.)

Take a look at the clock signals being generated on the I/O board and the CPU board - and confirm they're as expected.

Look at the INT line to the processor and confirm that it is not permanently asserted (if it is, trace this back to see why).

((You can try to restart the CPU manually, by reasserting the reset signal while everything else is powered up. If this works then we might be looking at a power on/power up issue)).

In summary - when the board is failing to boot, go around the system and look for any unexpected behaviour/any behaviour that might prevent further booting.

Csaba Zvekan [21030495] · Thu, 8 May 2003 14:46:36 +0200

All the Leds are on . Always ! How do I check the if the processor is out of reset ?

David Clarke [21030085++] · Thu, 08 May 2003 20:26:07 -0400

RESET is an active low signal on pin 37 of the 6809 (Z1) on the CPU board. Look at this pin. If the voltage is 5V or so, then reset has been de-asserted. If the voltage is 0v or so, the processor is being held in reset (use the schematic and start to trace back towards where the signal is generated on the power supply).

If reset is OK, then quickly look at Z1 pin 38 (main CPU clock)and then dig in from there.

Csaba Zvekan [21030495] · Fri, 9 May 2003 09:37:41 +0200

Here are my results :

RESET is an active low signal on pin 37 of the 6809 (Z1) on the CPU board. Look at this pin. If the voltage is 5V or so, then reset has been de-asserted. If the voltage is 0v or so, the processor is being held in reset (use the schematic and start to trace back towards where the signal is generated on the power supply).

I have 5.110v on pin 37 on (

If reset is OK, then quickly look at Z1 pin 38 (main CPU clock)and then dig in from there.

On pin 38 I have a nice sine curve of 1.562v of maybe 100-150 ns of width

This is a mystery Chroma

Serial No

Csaba Zvekan [21030495] · Tue, 6 May 2003 23:25:44 +0200

Hi,

I'm trying to find out the serial number to my unit.I have 21010261 on the Plate in the back. But on the Wood inside the Machine I have 21030495. Perhaps the Power Supply was Swapped at one point ?

David Clarke [21030085++] · Wed, 07 May 2003 21:05:54 -0400

That's most likely what occurred. I would refer to the unit by the S/N inside, and then just note that it has the other S/N marked on the outside (I have a Chroma Expander that actually has a Rhodes Chroma S/N tag on it - and I know for sure that it was the result of a power-supply swap at a repair shop).