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ChromaTalk Archives: February 2020

Chroma for sale - 21030058

Joe Porter [21030058]

Hi all,

I'm thinking of selling my Chroma, I just don't use it enough anymore.

It's 21030058, in UK. It was fully serviced by Ben at CyberWave a few years ago (Cyberwave EMS: Our Clients), who is the guy to service them in UK. He also sorted out two extra voicecards I have, so you'll have two spare as back up. He did a great job, background hum is non-existent, you plug it in and think you haven't until you hit a note.

Also, comes with the original pedal. CC+ and SPSU, so all the required upgrades are in.

It's an early one, so quite a lot of the boards are white Arp ones and has been in my smoke-free studio since I bought it in 2009.

I'm selling for £8,500 (GBP) + shipping, which is a couple 1,000 cheaper than the last I saw go like this.

Any questions, let me know.

Paul Hackett-Evans [21010094]

Hi Joe, I've emailed you off group. Please let me know if you receive my email, it will have my Gmail address not the one.

almost healthy chroma

ulfur hansson

dear list,

been a while since i did any work on my chroma - i spent about 9 hours socketing and replacing all logic chips on i/o board. it now boots up and sounds amazing again!!

i learned that the ribbon cable connecting the i/o board to the keystack boards had gone bad and shorted 5v to ground (what bad luck!) i replaced the ribbon and also replaced all ic’s on switchstacks with sockets/new ic’s.

now the left side of the keyboard plays beautifully, but the right side does not - if i play a key on the right side of middle C, the entire switchstack bucket will fire at once and the keyboard scanner locks up/stops working.

i am at my wits end here, so close to the finish line. is there anything that could cause an issue strange like this only on the right keystack switch board? maybe the keystacks themselves?

i have checked for shorts on all ic’s on keystack boards, and each individual keystack switch as well....

any help would be greatly appreciated!

all the best,


ulfur hansson

since left keystack is being properly interfaced with by Z34 and Z35 on the IO board - would it be reasonable to think that nothing on the IO could be causing problems with the right keystack board?

Paul DeRocco [21030230]

Probably. What tools do you have? And what did you mean by "the entire switchstack bucket will fire at once"?

ulfur hansson

hello paul,

apart from soldering i have an oscilloscope, multimeter, and a hakko desoldering gun..

by switchstack “buckets” i mean the last switch on each group of eight switches will fire all of the eight notes in that group. but only the last switch in the group will fire, the others are dead silent.

what kind of logic error would cause thia behaviour?

i really appreciate your help.

all the best,


Marc Pomeroy [21030419]

Same thing happened to me. Check all the resnets, especially Z6 and Z9 for shorting across resistor paths in-chip. Each resistor should be completely isolated. I found some continuity between resistors. Swapped out all the resnets and solved it.

Technician Larry [21030198]

Symptom reminds me of a keyboard problem on some synth decades ago where a broken contact wire was shorting out a couple of scanning bits when a certain key or keys were depressed. Don't remember much about it other than a thorough visual inspection would have revealed the issue and saved a bunch of scope probing and circuity analysis.

Paul DeRocco [21030230]

If you mean that note 63 (high G, if numbered from 0) causes notes 7, 15, 23, 31, 39, 47, 55, and 63 to play, then Z1 is dead, and its pin 9 is permanently pulling down. If you mean that playing note 63 causes notes 56, 57, 58, 59, 60, 61, 62, and 63 to play, then I haven't a clue.

RIP Lyle Mays

Brian McCully [21030361]

Lyle Mays, jazz keyboardist with Pat Metheny Group, dies at 66 - The Washington Post

15 seconds into the video there's a picture of a Chroma under the Oberheim...

I had a chance to speak with him backstage at a show and he said that he used the Chroma like for 95% of his solo album. I remember seeing him flashing the Chroma's auto-tune throughout that show.

One of the absolute greatest shows I ever saw was his trio at the Berklee Performance Center with Marc Johnson and Peter Erskine. He was a phenomenal - like a musical cross between a grand chess master and an octopus, always many steps ahead.

Saw the PMG many many times...

Thanks for your contributions, Lyle !