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ChromaTalk Archives: November 2001

Service Notes

Chris Ryan [21030691] · Thu, 1 Nov 2001 07:42:47 -0800

I've posted the first set of Chroma Technical Service Bulletins. The eight "Service Notes" cover a variety of topics; several are of historical interest only but are included for the sake of completeness.

Field Change Notices, which are more detailed and include schematics, to come.

Re: Rising Chroma prices

Go to first message in thread (October 2001)

Joakim Uddling [21020003] · Sat, 03 Nov 2001 18:27:49 +0100

I don't think so, because normally Chromas go for between 2000 and 2800 DM (between 1000 and 1400 US$ approximately) here in Germany. I've never seen someone asking that much before.

I fully agree on this. As a first bid it is far too high. And the guy actually have repeated this auction three times without any bids at all...

Request for Pics/Schematics of Aftertouch/Pressure Unit

David Clarke [21030085++] · Sun, 11 Nov 2001 13:05:19 -0500

A while back there was discussion of at least one keyboard owned by a list member that did have an aftertouch/pressure unit installed.

Is there anybody out there who now has this keyboard (or has another unit that does have the aftertouch unit installed)?

If so, it would be nice to have pics/schematics of an actual unit avail. at the site.

Dave later acquired a Chroma with a pressure sensor and wrote and contributed The Chroma Pressure Sensor & Interface.

Calling Mike Maloney

Fred Warren · Thu, 15 Nov 2001 13:46:10 EST

Does anyone know how to contact Mike? I'm trying to follow up on his production of reset boards.

Thanks!

No one ever tracked down Mike. [August 2004]

The long story of my broken Chroma

Sandro Traversi [21010217] · Fri, 16 Nov 2001 13:04:19 +0100

Hi All.

I'm a guitarist tripped in synths since middle '80s, missing a bargain ARP 2600 at $250.

My exploited passion drove me to purchase a Korg MS20 in 1987, then an OB-X and some other digital stuff in the past years.

I've always kept the Chroma in my mind as something unreachable very rare in Italy and a price in 1983 as present $ 8000... but, I got a chance.

I bought my Chroma (serial # 21010217) in Sept 2000 from Stefano Galante (see Chroma Registry) strongly encouraged by the rich infos of your site and mainly by the great entusiasm of the all Chromas maniacs, not the last Luca Sasdelli (see again Registry) who was very generous about tips & tricks in first repairings.

Chromas conditions ? Bad enough. It wasn't played since 8 years, stored in Anvil case .

Opened up, it looks enterely covered on the sides by the Anvil case foam and, mainly, absolutely silent ; no manuals , but a sustain pedal at least (maybe DeArmond).

Then, I began restoration and repairing activities I'm still in.

First, I cleaned the foam on the wood sides spending 2 days of very big work and an oil used to refresh wood. Results were good enough and now I enjoy its very nice cherry sides.

Metal and mylar panels were cleaned using a kitchen spray in Italy marketed as Glassex.

Also the keyboard needed some work, so i pulled out each key one by one and cleaned them by a spirit-water solution.

I also enterely opened the Chroma so to clean it from some small foam pieces inside; i used an air-compressor and then a vacuum.

At last, keyboard has 5-6 keys functioning erratically; so i sprayed a bit of isopropilic spray and passed a piece of paper between the aluminum lamels everything ok.

After all these activities now my Chroma has a pretty good used look.

Few days pushin down keys and buttons and I found out it was absolutely with no patches and that only ONE Dual Channel Board was functioning (#4), as Data Readout was displaying "E0123567" (aaargh !!!).

So, I started cleaning contacts and mainly DCB pins (P5 P6 P7 P8) using isopropylic spray.

This gave me one more DCB (#5) , but I still had to repair the others 6 and I'm NOT an engineer nor an electronics expert , anyway I got an experience in building a guitar effect kit years ago (... I know its not enough ...) .

I found as a really great help both the downloaded Service Manual and the Chromatalk mailing list.

Then I spent about 3-4 months attending to few some principles about electronics (very few) and mainly working on a very deep analisys about Dual Channel Boards functioning as reported in the Service Manual. Its the first and the only one Ive read, but I value it as a basic course in synth electronics.

I tried to fix the first DCB with such an instrumentation like a solder , a solder-pump and a cheap DVM no scope.

I also layed down a flow chart about standard voltages and audio signal paths inside DCBICs, looking at functioning DCB as a reference. In fact I found that its possible to hear audio signals just from early ICs in the DCB i.e. both Z2 and Z3 put out an audio signal at pin 3 listeneable by a headphone (a head on the pin and the other pulled to ground).

So, following the DCB circuit, you can hear at which point audio signal stops and then find a maybe broken IC !

I fixed 5 (!) DCBs by a such empiric (but gratifying) method, checking every DCB , finding broken ICs and doing substitutions with new ICs on sockets .

Now I also got an IC cemetery, mainly populated by CMOS switch (4051 , 4052) expecially which used in the Sample&Hold DCB circuit (Z19 & Z20).

Im really proud about this work and I really enjoyed 14 voices for a while , but unfortunately, not too long...

Just some weeks. In fact, during my trying to fix DCB #7 (still not fixed) I suddenly found my Chroma again broken and silent , so repairing became neverending.

All above happened about March 2001. Months after Ive been sinked by my job and ... a home moving and ending of my new house building ! But now I have restarted fixing, as I dont want to give up.

First new repairings in October regarded some oxided traces on PCB and Ill avoid to detail it here.

On 1st November 2001 I finally re-booted my Chroma, and here below ive reported the actual working conditions of my Chroma at the present time.

BOOT 1 (1st Nov 2001)

At the boot , its leds blink just one time & data readout displays <Err01234567>

Immediately you hear no sound playing keyb gets no sounds

After 5-10 secs (not touching keys) you can listen a very slow attack sounds grewing up in volume in a big mess , I call it microtonal choir just like all oscillators whistling randomly or auto-oscillating all at a fixed hi-frequency after a slight pitch ramp.

  • Autotune has no effect - no leds multiple blinking and everything going on as above.
  • Set split 50 does not restart this microtonal choir - it goes on.
  • Set Split 6 is ok showing CELL 3,18
  • Set Split 30 light every leds (after SS30, display remains showing 88 - its ok ?)
  • Tapper works and Set Split 9 well dis/activate tapper.
  • Panel buttons work
  • CPU seems to be working as it changes Parameters and Patches (almost as I can see by the leds and the display...)
  • Parameters ranges are correct (i.e. P33 goes 0-3 , P37 0-1 , P1 0-15 , P41 63+64 , P50 0-7 , P19 0-31)
  • Trying Standard Parameter Value Procedure (holding Parameter button and #1 , #2 , ... ) it seems to work
Checking voltages (but my DVM is a cheap one... ) I found :
  • GND = 0,00
  • +5Va = +5,09
  • +12V = +12,23
  • -12V = -12,18
  • Dgnd= +0.08

I also measured +5V digital in several point along I/O and CPU boards, with such values ...

  • I/O (centre board) = + 5,05
  • I/O (right side) = + 5,01
  • CPU (left side) = + 4,97
  • CPU (right side Z5 pin) = + 4,85

Ok, my DVM is cheap , but this descending curve must mean anything , or not ?

Turned off the Chroma.

Boot 2 after 15 seconds.

Fuse blows.

Boot 3 after 5 minutes

Ok , no fuse blowing...but same stuff as 1st boot

now I check on DCB #3, using a headphone (-pin on GND)

  • +pin on Z3 pin3 (vco out) = i hear a very hi freq ... as some hi freq on AM radios ...
  • +pin on Z2 pin3 = just like Z3 above
  • if do Autotune , both Z2 Z3 gets outs a fixed audio frequency interesting !
  • if Set Split 31 I hear that audio frequency just for sec , then I hear hi AM freq. again

On Z8 (wave selector IC) pin 2 and pin 4 give WHITE and PINK Noise as feeded from Channel M/b so this seems ok

Boot 4 (2nd Nov 2001)

Fuse blows.

Boot 5 (after 2 minutes)

Fuse blows again.

Boot 6 (after 2 minutes)

Everything as reported in Boot 1.

Turn off Chroma.

Boot 7 /(after 30 minutes)

Fuse blows.

Now I must say about some strange episodes happened in March 2001 during first repairings , when anyway Chroma WAS functioning.

  1. 1 after 3-4 fuses blowed at boot , I changed the fuse not with a 500mA type BUT with a 1 A type - how bad I did ?
  2. 2 in Parameter mode on Patch #3 , after varied a value and without saving , I select a new Patch just played a key, Chroma had a crash
    • doing the same a 2nd time, it crashes again and activate the tapper (?)
    • doing the same a 3rd time , it crashes again and losted all the patch in memory

Why that strange things ?

Boot 8 (8th Nov 2001)

Everything as reported in Boot 1, microtonal choir , patching & editing mode seem to work, ... but in this

boot I discovered something interesting using Set Split 31 mode (special reset).

After doing SS31in fact Parameter changes seem to have effect, but Ill be fair :

Chroma doesnt play real notes, but noise , fixed frequency , whistle or very random notes, absolutely not chromatically related to the keyboard.

Yes, in Set Split 31 mode it answers to keyb calls.

  • P33 works
  • P37 works
  • P38 works
  • P1 works
  • P34 works
  • P8 til P25 works
  • P26 P27 seems to work
  • P46-P50 seems to work
    When I say work it means I hear a direct effect on that odd sound played by the Chroma
  • P39 also seems to work. but I hear a lot of sub-noise (current in audio path ?)
  • P3 is very strange if it has a value > 5 Chroma plays microtonal choir
  • If it has a value < 5 Chroma plays very strange random notes or delays or arpeggios ...

and more , every time I pull down a key I also see Display and DataReadout leds as turning off and on as a great current consumption.... (???)

At last I tried also Set Split 29 (Osc muting) , and it also well works muting all the oscillators from that nightmare !

Thats all folks!

Now , I m a bit gived up and i dont know how go on fixing.

I have some suspects about the KEYB SCAN CPU or maybe BAD RAM or . dont know.

I also suspect that the power supply could had broken or altered funtioning, maybe also in past times, maybe before I bought it !

Anyone in the list would be so kind to help me in diagnosticing all that mess or show me the right way ?

Sandro Traversi
Italy

Jerry Leonard [21030100++] · Fri, 16 Nov 2001 20:08:21 -0800

Reference your November 1st boot. I had exactly the same symptoms, but at no time ever blew a fuse. I don't remember exactly what I did to get past that, but I do know for sure that the problem was on the I/O board, not the power supply or reset circuit, since I had both of those (power sup and reset circuit) replaced / built and they work perfectly. I think that the problem ended up being in the circuit on the I/O board that was an interface to the computer board. Sorry I'm not much help. Dave Clarke is pretty good electronically, I'll bet he would have a pretty good idea for you.

David Clarke [21030085++] · Sun, 18 Nov 2001 10:46:29 -0500

Based on the tests you did, it appears that the power supply voltages are generally OK (both at the power supply and on the boards that will need the power). Further, it looks like the Chroma will respond to panel key-presses (set-split 31, etc.) That tells me that the CPU and ROM are probably OK.

The Err01234567 can be caused by a single bad voice-board.

To diagnose further I would recommend removing ALL the voice boards.

I would then put 1 voice board back, and restart the Chroma. See if the display now has one less Error number (i.e., Err 1234567).

If it does, repeatedly try each of the voice boards in turn as the 'only' voice board in the system.

You can then try a known-working board in each of the voice board slots.

By doing these tests you can hopefully narrow down whether the problem is related to a specific board or a specific board location (or both).

Once you know what boards/slots are OK, you can put them back and see if the system now boots OK.

Note: be careful when putting boards in/out - it is very easy to accidentally 'miss' the connector with the pins (or to bend the connector back).

Hopefully this will work - if it doesn't, then the best way to go further would be to find someone with an oscilloscope who can help narrow down what is going wrong.

Jimmy Moyer [21030184] · Mon, 19 Nov 2001 02:03:43 EST

I'd add that since it is so easy to mis-seat the dual channel boards, it is a good idea to closely examine where those connectors meet the boards for hairline (or worse) breaks.

Sandro Traversi [21010217] · Tue, 20 Nov 2001 14:47:50 +0100

Based on the tests you did, it appears that the power supply voltages are generally OK (both at the power supply and on the boards that will need the power).

Just last days I read Service Bulletin # SN3-008 and #SN3-006. I also think PSU is OK , BTW I executed procedure in SN3-006 , setting R22 so that +5v Analog was +5,05 (before it measured +5,09) and also setting offset null between TP0 and TP1 = 0,000 in the I/O board.

Did it bad ? Anyway no effects on my Chroma.

Soon I'll change also fuse with Slo Blo type.

Further, it looks like the Chroma will respond to panel key-presses (set-split 31, etc.) That tells me that the CPU and ROM are probably OK.

I agree.

The Err01234567 can be caused by a single bad voice-board.

(!) that's a news for me.

To diagnose further I would recommend removing ALL the voice boards.

I would then put 1 voice board back, and restart the Chroma. See if the display now has one less Error number (i.e., Err 1234567).

If it does, repeatedly try each of the voice boards in turn as the 'only' voice board in the system.

You can then try a known-working board in each of the voice board slots.

By doing these tests you can hopefully narrow down whether the problem is related to a specific board or a specific board location (or both).

Once you know what boards/slots are OK, you can put them back and see if the system now boots OK.

Done last evening.

I used for this test DCB #4 , maybe the best I got, having all original parts , never needed fix and more stable than others.

I swapped it in each slot from #0 to #7, rebooting each time with such these results :

  1. No fuse blowed on 7 boot
  2. On slots # 0-2-3-4-5-6-7 it showed the same sympthoms - no sound no noise
    • Just a very tiny whistle very very low in volume.
    • Set Split 50 and Autotune do had no effect.
    • Set Split 31 too, but changing P33 (waveshape) on values 3-2 I listened to White and Pink Noise , always on very very low volume
  3. On slot # 1 , just booted you can hear a great double whistle - very big in volume
    • Set Split 50 and Autotune do had no effect
    • In Set Split 31 mode also changing P33 on values 3-2 I listened to White and Pink Noise , now on very very high volume

So it seems to be something wrong on slot # 1.

Looking at the Channel M Board and DCB schematics , I noted that almost every signals (DAC, SHA, DATA, NOISE, OSC EN, Voltages) share common paths towards Dual Channel Boards.

Except for Data Strobe Decoder which gives individual signals for each single Channel.

So now I have a big suspect on Z13a on Channel M board, the only one IC dedicated to give Strobes to DCB # 1 (please, slot) .

Am I thinking right ?

If so , it's possible that Z13b still works well ? It's the same IC !

Anyway , I think to buy a 4556 as soon as possible to change it - it's not a big deal .

What's your opinion , Dave ?

Note: be careful when putting boards in/out - it is very easy to accidentally 'miss' the connector with the pins (or to bend the connector back).

Yep, sure I am ! ;-)

Hopefully this will work - if it doesn't, then the best way to go further would be to find someone with an oscilloscope who can help narrow down what is going wrong.

Where do you narrow down exacly ?

I got a old tube scope , but I don't know how manage it . Could it be useful ?

Maybe I'll got a friend electronic tech to kidnapp to examine my Chroma. In that case which & where I 'd to check ?

Many thanks.

Sandro

David Clarke [21030085++] · Fri, 23 Nov 2001 21:10:28 -0500

  1. On slots # 0-2-3-4-5-6-7 it showed the same sympthoms - no sound no noise
    • Just a very tiny whistle very very low in volume.
    • Set Split 50 and Autotune do had no effect.
    • Set Split 31 too, but changing P33 (waveshape) on values 3-2 I listened to White and Pink Noise , always on very very low volume

It would be good to create a "scratch" patch by (by holding down the parameter button while pressing each of the parameter buttons). I suggest doing this once and then storing it in patch location 1 (to help with your debugging).

So it seems to be something wrong on slot # 1.

If you put cards back in slots 0, 2, 3, 4, 5, 6 and 7 (i.e., only skipping #1) can you get it so the display only shows Err 1 ?

So now I have a big suspect on Z13a on Channel M board, the only one IC dedicated to give Strobes to DCB # 1 (please, slot) .

...

If so , it's possible that Z13b still works well ? It's the same IC !

It is certainly possible that you can loose a single gate in an IC. If all other slots work, then you may have identified the bad part.

Anyway , I think to buy a 4556 as soon as possible to change it - it's not a big deal .

What's your opinion , Dave ?

Yep - sounds good. I'd buy a couple 4556's (just to have).

Maybe I'll got a friend electronic tech to kidnapp to examine my Chroma. In that case which & where I 'd to check ?

If you can get a couple boards that work fine, then the easiest way to proceed is to trace the signal coming in on a 'good' board and a 'bad' board and see where the 'bad' board starts to go bad (using the schematic to guide you).

See follow-up discussion in the December archives: New troubles on broken Chroma.

Eprom types / Bad voices

Josue Arias [21010162] · Mon, 19 Nov 2001 11:47:29 +0100

Hi People,

I'm in the process of changing the software revision for my chroma, from 1.2 to 1.4. just downloaded the eprom files and I found a guy that can burn them. Now my question:

At the chroma eprom code page, it says that chroma rev 1.2 and 1.4 eprom are intel-2716 and chroma expander eproms are AMD-9716DC for rev 1.2 and MM2716Q for rev 1.4... Looking at my eproms they are rev 1.2 and the chips are AMD-9716DC. Can I burn the 1.4 code over the AMDs or I need to get new intel-2716? may be all off these chips are the same chip for different brands and I can burn the eproms in all 2716 compatible eproms??

Thanks!

Josue Arias.

PS. Finally I'm trying to fix my bad board for myself. As Till said, is easy to track the problem. I'm a newbie at electronics, I just built some modules for my modular and repaired some synths with minor problems but is still easy.

Now I've found the filter, VCOs and VCA seems to work and the problem is in the pitch info. The problem is at the voice board, not main board so I think is a bad CD4051. I'll go today to the electronics shop to get a couple and try it...

I'll keep you informed.

Sandro Traversi [21010217] · Mon, 19 Nov 2001 16:38:24 +0100

Hi Josue,

if you take a look to my previous mail (long story...) I reported CD4051 not working as a frequently featured malfunction in DCBs.

I changed a lot of them and swapped with HCF4051, as RCA type are too hard to find.

Buy and change them with no worries - they will not affect sound and ... are very cheap !

Josue Arias [21010162] · Mon, 19 Nov 2001 21:24:20 +0100

Hi Sandro,

I just desoldered the ic19 & 20 i'll try the new ones in a few minutes ...;-) About your chroma love-hate story, yes I've readed the complete history, keep us informes when you try the vince advice. I apologize for your problems regarding the chroma, but in the other side, you'll get a Master in electronics for FREE!

David Clarke [21030085++] · Tue, 20 Nov 2001 19:40:26 -0500

Josue Arias said:

Hi People,

I m in the process of changing the software revision for my chroma, from 1.2 to 1.4. just downloaded the eprom files and I found a guy that can burn them. Now my question:

At the chroma eprom code page, it says that chroma rev 1.2 and 1.4 eprom are intel-2716 and chroma expander eproms are AMD-9716DC for rev 1.2 and MM2716Q for rev 1.4... Looking at my eproms they are rev 1.2 and the chips are AMD-9716DC. Can I burn the 1.4 code over the AMDs or I need to get new intel-2716?

You can certainly use the exact same chips over again, if you like (i.e., take the AMDs you have, erase them and put the code in them).

may be all off these chips are the same chip for different brands and I can burn the eproms in all 2716 compatible eproms??

Yes - as long as you have an equivalent part, you can really use whatever manufacturer's part is available.

xls parameter chart

Sandro Traversi [21010217] · Mon, 19 Nov 2001 17:11:30 +0100

Hi list.

Chris has been so kind to add in Parameter Chart Page a link to an Excel file [111K] I enjoyed to make.

Is has no ambition to be perfect, but I think it could be useful and easily customizable.

Chroma for auction on eBay

Dave Bradley [16330135] · Mon, 19 Nov 2001 21:33:37 -0600

With Syntech MIDI, pic looks pretty darn clean, location is Minneapolis... [item 1485914536]

Here's the picture:

Chroma Spotting

David Clarke [21030085++] · Sat, 24 Nov 2001 21:22:21 -0500

In case anyone is keeping track, a Chroma can clearly be seen in the video for the song "Live is Life" by the group "Opus" (circa 1984).

Paul Hackett-Evans [21010094] · Sun, 25 Nov 2001 11:31:47 -0000

Chroma and Polaris spotting

To add to David's thread (good idea!) -

Spandau Ballet used a Piano (Yamaha stage piano, I think) and a Chroma as the only keyboards on their 1983 album "True" and its 1984 follow-up, Parade. You can often see a Chroma in the videos accompanying the singles and in their live video. An amusing aside here - Roy Paynter, the UK's best Chroma engineer told me he was asked to service their Chroma at the end of a tour in the 80s. He met their road crewto take the Chroma to his workshop. Their keyboard roadie was a very big guy. Once Roy had made himself known, the roadie asked him to wait while he fetched the Chroma. A few minutes later, the roadie returned, carrying the Chroma in its Anvil flightcase, hoisted up on one shoulder, walking along as if it weighed nothing at all! Yowch, most of us can barely pick the things up at all on our own, never mind on a shoulder with one hand! Now that was some roadie!

In the 1980s movie "He-Man And The Masters Of The Universe" starring Dolph Lundgren, the high-school band's keyboard rig features a Polaris which gets a lot of screen time, including a scene where Skeletor's evil minions set fire to the building, You can clearly see the Polaris going up in flames. Dammit!!

There is also a pop musicpanel game show on TV here in the UK called "Never Mind The Buzzcocks". The background of the studio set for the show is a dark area behind the panel, with a variety of instruments picked out with blue spotlights. A Polaris is one of them.

Anyone have any more "spots"??

David Gowin [21030611] · Mon, 26 Nov 2001 09:11:23 -0500

Re: Chroma and Polaris spotting

Another Polaris on a modern show (not sure if you guys in the US can get it) is Open Mike with Mike Bullard, a Canadiab late night talk show. The keyboardist in the band uses a Polaris as part of his rig.

Jeff Bova [21030407++] · Sun, 25 Nov 2001 09:46:13 -0500

Chroma Sightings

I vaguely recollect a video where Garth Hudson(The Band) is using a Chroma. Has anybody else seen it?

Chris Ryan [21030691] · Sun, 25 Nov 2001 09:35:25 -0800

Re: Chroma Sightings

There's a Keyboard Magazine interview with Garth Hudson, with a few mentions and a couple of pictures of the Chroma, here:

http://theband.hiof.no/articles/keyboard_magazine_garth_1983.html

Robert Shanks [21030301] · Sun, 25 Nov 2001 22:47:44 -0400

Re: Chroma Sightings

Not a bad litlle rig... A Chroma & a CS-80. Yeeha!