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ChromaTalk Archives: February 2005

Hardware Fault Diagnosis & Repair

Chris Ryan [21030691]

Martin Straw, a former Chroma tech from the UK, has kindly contributed detailed information for checking and repairing a malfunctioning instrument in "Hardware Fault Diagnosis & Repair."

Any comments from the technicians on this list would be welcome. Dave has already contributed a note about voltage values on giant capacitor C3.

Werner Schöenenberger [21010114]

Hi Chris,

this is famous information. Thanks a lot to share it with us (and many thanks to Martin Straw, of course)

Erik Vellinga [21010286]

Chris,

The new Chroma site is great ! I feel exclusive owning a Chroma... There are no problems in navigating or missing files. Compliments a lot !

Some music though would be great. But I think it is now one of the best in Synth info sites i have seen. It lookes like all the effort for putting it in to the market back in 1980's is continued, for the love of this instrument!

Thanks Chris !

Jesper Ödemark [21010135]

That's a resource I call worth its name - great work Martin & Chris!

Chroma on eBay Australia

Chris Ryan [21030691]

Looks to be in very good condition. $999 starting bid; no bids yet, ends February 8. Newcastle, New South Wales. Item #3779973673.

This is Chroma 21040006. The seller writes, "This belonged to Ian Hails of Singleton NSW, who sadly passed away about 4 years ago. He bought it new in Sydney about 1983 according to his widow, paid a fortune for it then, about $7500 AUD. It is in great condition, he loved it dearly I was told."

Werner Schöenenberger [21010114]

Lucky Australian guys who might bid on this instrument ;-)

Werner, living far away from Australia

Jesper Ödemark [21010135]

I have a friend who is pesterising me about buying mine - I will tell him about this one.. Might be work the money to get it to Sweden...

Chroma on eBay

Chris Ryan [21030691]

Asking £1100; no bids yet; ends February 28. Sydney, New South Wales, Australia. Has the Hutchings Keyboards logo on the back panel. Could be 21040006, which was for sale earlier this month. Item 7301981902.

One of the pictures:

Jesper Ödemark [21010135]

Aren't those Music store stickers cute and a good historical reference. Mine still bears its "Music City Köln-sticker".

Chroma Problems HELP !!

Larry C [21030864]

Hello all:

I am the owner of Chroma SN 21030864. Been a member of this list for years and watched as many very talented people here helped people with chroma problems. (I only wish I knew more about electronics, since I own a few other synths besides the chroma.) My chroma died a few days ago, and I am asking for your help now.

I opened the chroma to check if the batteries were leaking, I had been meaning to do this for a while but until now I haven't had the chance. The LEFT battery was corroded at the bottom. The corrosion was contained to the battery holder, but I suspected the Vapors might have caused some problems. I removed the Computer board and replaced the battery holder, after I cleaned the PC board. I checked the board as carefully as I could and touched up a few of the suspicious solder joints in the area. Then I put the computer board. back in the chroma. Here is an exact description of what happened next.

I turn on the Chroma, all of the lights flash once very quickly, then the display reads 01234567. IF I press any of the link, parameter, buttons they all cause the tapper to tap, and the lights go on as normal WITH ONE EXCEPTION. The set-split button, the light does not come on, but the tapper taps.

IF I try to perform a Set-split on any of the functions (for example set-split 9, 6, 50) nothing happens.

If I press any of the 50 presets the number of that preset shows up in the large display. I can change any parameter of any patch and store it. Incidentally , I can load patches into the chroma using the cassette interface. I checked the powersupply voltages and they are as follows +12.18 -12.18 +5.07 and the tapper +24. I started to go thru the repair instructions on the website but after measuring the voltages on the power supply I dont know what to do.

Apparently none of the voice cards tune, there is no sound. I pulled all of the voice cards, and put a few back in randomly to try to see if one of the Voice cards was causing the problem with the tuning circuit.

Please let me know what you think,

Best Regards,
Larry

David Clarke [21030085++]

Larry - a couple questions to maybe help us determine what might be going on:

  1. You had noted that the Chroma died a few days ago. What more can you tell us about that (i.e., was it working OK before the battery holder clean-up - or was the battery issue only noted afte the chroma stopped working? If the latter, then when was the last time it was working OK, when it died, what happened. Is/was the behaviour you saw at that time the same as what you're seeing now, or something different?)
  2. If you do a Set-Split 31, (special reset), can you get any sounds out of the Chroma?
  3. If there's a MIDI interface installed, does pressing the keys down generate MIDI out data?
  4. Has it been double-checked that none of the small pins on the CPU cables have accidentially been bent over at the time of re-insertion?
  5. Did the Set-Split LED work OK before the problems started?

Larry C [21030864]

Thanks for the questions, I will give you as much detail as I can to the following questions

  1. You had noted that the Chroma died a few days ago. What more can you tell us about that (i.e., was it working OK before the battery holder clean-up - or was the battery issue only noted afte the chroma stopped working? If the latter, then when was the last time it was working OK, when it died, what happened. Is/was the behaviour you saw at that time the same as what you're seeing now, or something different?)

I was reading thru the Chroma Archives and I came across a battery reminder which someone posted. I thought it might be a good Idea. I once had a POLYSIX and had quite a mess cleaning up the battery damage to the board, so I opened my Chroma up BEFORE I even turned it on. Sadly I dont know the state it was in before the battery holder clean-up. The last time I used the chroma was about a month ago and it worked perfectly fine. I only wish I had turned it on before I replaced the battery holder and did the clean up.

  1. If you do a Set-Split 31, (special reset), can you get any sounds out of the Chroma?

The problem is that I cant do a Set-Split anything. IF I press the set-split key the tapper makes the tapping sound, but, lets say I do a Set Split 50, nothing happens it is as if I just called up Patch #50. It kinda ignores the fact that I pressed the set split. If I remember correctly, a few months ago , when I pressed Set-Split the yellow light would blink, then I would press the corresponding number and it would execute that command. Unfortunately it doesn't do that now.

  1. If there's a MIDI interface installed, does pressing the keys down generate MIDI out data?

There is no interface connected to the Chroma. I will connect one and see if it generates MIDI Data and let you know.

  1. Has it been double-checked that none of the small pins on the CPU cables have accidentially been bent over at the time of re-insertion?

I will Double check the small pins on the computer board, I assume you are talking about the (2) flat cables that connect the Computer board to the I/O Board.

  1. Did the Set-Split LED work OK before the problems started?

Yes the Set split worked fine.

David Clarke [21030085++]

I will Double check the small pins on the computer board, I assume you are talking about the (2) flat cables that connect the Computer board to the I/O Board.

Yes - correct.

In addition I'd also look very carefully at all of the electrical connections which go to those cables on the CPU board (the schematic in the service manual should help to trace these back to their source on the CPU board - to make sure all is well).

(The top connector - the one closest to the edge of the board, marked J10 - carries address and data signals to the I/O board, and some of those signals get routed around/under the battery holder. Since work was recently done around there - this would be a prime area to review.)

Larry C [21030864]

I really want to Thank You agclarke for helping me with this problem.

I checked the connectors going to the I/O board and all of the pins are fine. I am going to check all of the connections which you mentioned on the Computer board.

After reading your question about connecting midi to the unit, ( I am using the chromaface). I connected the midi interface and tried to get midi signals out of the Chroma but I could not get any midi data coming from the Chroma.

Thanks again,

Larry

Larry C [21030864]

Chroma Battery Nightmare

A quick update on my beloved Chroma and the attack of the Akalines.

As I stated before, the batteries had oozed their clear liquid all over the left bottom of the CPU board. Upon closer examination I noticed that the clear liquid had run down the rail (angled piece of iron which runs across the Chroma) and dripped into stack switch assembly #18. The Chroma sat in its case (we moved recently), resting on its back, which caused the liquid to flow over the rail and drip on Voice card #5. As it ran down the voice card it deposited a wonderful blob of clear liquid directly on top of CMOS chip 4556. I dont mean to be critical of the synth design but I only wished synth designers who choose to use Akaline batteries would locate them inside the synth in a safer place.

I am beginning the restoration of my chroma SN 21030864. If anyone could please suggest chemicals/cleaners for PC boards which would help, I would be most appreciative. Apparently this stuff is extremely conductive and I would like to remove it in the best way possible. I realize I will probably have to remove and replace severely damaged components. Any suggestions would be appreciated.

Jesper Ödemark [21010135]

Re: Chroma Battery Nightmare

Hi!

Sad to hear, but good you found the reason and could track the course of the liquid. I have a friend who has cleaned a few Polysixes so let me know if you don't get any good answers and I'll check with him...

Not to be an ass, but I guess the builders didn't suspect it to last +20 years and not living in its case...

Check those battery synths on a regular basis! Does anyone know where the fluid "hits" if the Chroma is located as it should?

Chroma difficulties

Richard Ardery [21030562]

Hello

I have a Chroma that is having some difficulties powering up and wondered if I could get some technical advice on its probable source.

When initially turning on the Chroma after not having been played for several weeks, none of the lights come on and no sound can be generated. After letting the synth heat up for an 30 minutes to an hour, it fires up the lights, tapper and produces sound after turning the power off and then back on.

It appears that when the Chroma has not been operated for a week or so, turning the power on turns on the lights which do not blink. No sound can be generated until the machine heats up and the switch turned off and then back on.

I am hoping to get a general idea of the problem so that I can lead a technician properly.

Thank you for your kind assistance.

Jesper Ödemark [21010135]

Hi!

Is it the original power supply? Sounds like it can be the bad guy here. They often break down due to underdimensions and that's one of the classic Chroma flaws... (or maybe the only)

David Clarke [21030085++]

... I have a Chroma that is having some difficulties powering up ... When initially turning on the Chroma after not having been played for several weeks, none of the lights come on and no sound can be generated. After letting the synth heat up for an 30 minutes to an hour, it fires up the lights, tapper and produces sound after turning the power off and then back on.

The 30 minute+ timeframe is a bit of a nice failure mode, as it will give a technician a reasonable amount of time to poke around while the failure mode is present.

Given that the keyboard seem generally dead for the 'warmup period', I would certainly direct my initial attention to the voltages being produced by the power supply - as well as the general behaviour of the RESET/Power OK signal going from the Power Supply to the CPU.

I am hoping to get a general idea of the problem so that I can lead a technician properly.

I'd expect that tech (with service manual in hand, which includes a discussion on the general voltages expected to be seen in and around the power supply) should be able to quickly narrow down the area of the problem.

It would certainly be best to take some measurements and start from a position of knowledge - but If I had take a wild guess, and wanted to go the brute force approach, I'd probably change the large, main capacitor in the Power Supply as a first step (followed by the small cap right beside it that controls the time delay for the CPU reset circuit).

Good luck, and let us know how you make out.

Richard Ardery [21030562]

Thanks David!

Parts for Sale

Chris Ryan [21030691]

Martin Straw [21010093+], author of the recently posted "Hardware Fault Diagnosis & Repair," has a number of Chroma parts for sale. Check out the Classified Ads page for details.

I fixed it!!!

Stu Ervin

Alas my dear od chroma had died. After reading all the helpful info on this list, I was able to zoom in on the L6OV6 7.4 volt Zener Clamp, Z4. Which was pretty hot with the main +5 sagged down to 1.8 volts.... I cut Z4 loose and now all is well. Should I worry about replacing it?? They appear to be obsolete.

Could I use i higher voltage capacitor for the 47000 UF 7.5VDC Sprague unit? What if this cap were rated at 40 VDC instead of 7.5 . Then Z4 is not required.

Also, alas, I have lost some patches in the CMOS program memory. 3, and 50, are both dead; others seem to have changed...... Helllpp..!.!.. Does anyone have a backup cassette of the basic factory preset sounds?

Jesper Ödemark [21010135]

Alas my dear od chroma had died. After reading all the helpful info on this list, I was able to zoom in on the L6OV6 7.4 volt Zener Clamp, Z4. Which was pretty hot with the main +5 sagged down to 1.8 volts.... I cut Z4 loose and now all is well. Should I worry about replacing it?? They appear to be obsolete.

I could've guessed, but substitues then?

Could I use i higher voltage capacitor for the 47000 UF 7.5VDC Sprague unit? What if this cap were rated at 40 VDC instead of 7.5 . Then Z4 is not required.

That's too techie for me. :(

Also, alas, I have lost some patches in the CMOS program memory. 3, and 50, are both dead; others seem to have changed...... Helllpp..!.!.. Does anyone have a backup cassette of the basic factory preset sounds?

They can be found on the site in different formats. I'm sure there is something you can use. Good luck!

David Clarke [21030085++]

I fixed it!!! & Replacement PSU Parts (Zener/Cap)

... Alas my dear od chroma had died. After reading all the helpful info on this list, I was able to zoom in on the L6OV6 7.4 volt Zener Clamp, Z4. Which was pretty hot with the main +5 sagged down to 1.8 volts.... I cut Z4 loose and now all is well. Should I worry about replacing it?? They appear to be obsolete.

Stu - glad to hear that the Chroma seems to be generally humming along.

Conventional wisdom from the list tends to indicate that you can live without the part - but personally I feel happier with it in place.

While the part is generally now only available through parts brokers, one of the list member did buy some and has offered to make them available (see Source for L60V6, August 2004)

Could I use i higher voltage capacitor for the 47000 UF 7.5VDC Sprague unit?

Even if you want to run with a replacement Z4 installed, I'd recommend running a main cap with a slightly higher rated working voltage (higher than 7.5V).

When I've replaced these caps in the past, I've used Panasonic GAA series items (47000uF, 25VDC, computer grade - approx. $20ea) - readily avail. through digikey.com under P/N P10074-ND.

Also, alas, I have lost some patches in the CMOS program memory. 3, and 50, are both dead; others seem to have changed...... Helllpp..!.!.. Does anyone have a backup cassette of the basic factory preset sounds?

You can get the patches from the site (and, if need be, the conversion routines can be used to create formats that you can use with the cassette interface).

Jimmy Moyer [21030184]

Re: I fixed it!!! & Replacement PSU Parts (Zener/Cap)

I also felt better with this in place. I do still have 8 of these on the shelf. If anyone needs one, I'll let them go for my cost, $16 each, plus shipping.

mystery box

Stu Ervin

Hello fellow Chromies ... Thanks for all your help getting my power supply back up and running. Its good now with 40 volt capacitors and no L6OV6.

I have a dead key I am working on now....

Can anyone identify my "Mystery Box", which is a thin black aluminum MIDI interface with 2 midi connectors in back and a ribbon cable coming out from under the case. Inside is an 80C31 in the old 48-pin DIP package and an EPROM with a penciled label that might say " 2.1 " .... I have no information for this box, don't know if it works, or what....

Would very much appreciate any wisdom you guys might share, thanks!!!

Mark Morton [21030526]

Sounds like the "chromacult " box, info is on site

David Clarke [21030085++]

Stu - based on your description citing the 80C31 and the "2.1 EPROM" you've likely managed to end up with a Chroma Cult/KMX/Syntech interface. (The JL Coooper/Chromaface is Z80 based).

You can take a peek at the pictures and see if this matches the hardware you have (there are versions of the box both with and without the "Syntech" lettering).

If this is the interface you have, you're in luck - as it is the best external MIDI interface available for the Chroma. The user's manual (and other notes) for this itnerface are also available at the link above.

The patches available from the Patch Downloads page of the Chroma site are generally also available in sysex format - that makes for a very quick and easy way to restore your voices via MIDI.

3 Chromas For Sale

Chris Ryan [21030691]

All need work; sold "as is." 1 may have MIDI. See Classified Ads for contact information.

Doug Terrebonne [21030114]

Are these the same 3 "as-is" ones posted last June?

Doug Terrebonne [21030114]

By the way, polyfusion@aol.com is synth dealer/broker Chris Youdell of AMS [site disappeared some time in 2010]... Lots of posts in the AH archives about him pro and con...

Chris Ryan [21030691]

Are these the same 3 "as-is" ones posted last June?

I asked him and, yes, they are the same ones. He writes, "All I can assume that as Julie is a tech she does no want to spend hours testing them to give a report when she is as ever totally overworked! So the deal is that they are 100% AS IS - no idea if they work 1% or 100% hence the low price. Of course anyone can come to LA to test them for themselves." I've asked him to clarify on price ($1500 vs. best offer); individual availability; and whom to contact.

David Clarke [21030085++]

$1500 for 3 keyboards. In my eyes, that's a pretty good deal.

Someone please buy these so I don't give into temptation (to buy them, fix them up and resell ...)

Jesper Ödemark [21010135]

If he was located over here he'd have a buyer!!!

de-foaming the Chroma

Robert Shanks [21030301]

Hi all,

Time to de-foam my Chroma. Has anyone come up with a good way to get the foam off the wood and metal. I've read about some attempts, but I've not heard anything like, OK, this is how you really do it. TIA

Doug Wellington [21030300]

I don't know about the metal, but the citrus stripper from Home Depot is what I used on the wood. Of course, you'll need to completely refinish the wood afterwards...

Chris Ryan [21030691]

Several of us have had some success with Goo Gone. However, it's a big job; I had CAE Sound refinish my Chroma; I'm not sure what they used to remove the foam, but they did a nice job of refinishing it using "tung oil."

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