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ChromaTalk Archives: May 2007

Fender Clip Art

Chris Ryan [21030691]

A couple of years ago I won an eBay auction for some clip art which was sent to Fender dealers. Among the guitars, amps, mixers, and drums were a couple of drawings of the Chroma, with ARP style slider caps.

Ron Joseph [21030042+]


Until you mentioned it I didn't notice but both of mine have the ARP style slider caps. 21030042 has Arp caps except for the Parameter control, which is the thicker variety. Probably a replacement. Another small difference which in retrospect makes sense. Use up as much of your old stock first. Anyone else have the Arp caps or a different set?

John Leimseider [21030434++]

The early Chromas had slidepots with plastic shafts, the later ones had metal shafts... The knobs aren't interchangeable. The knobs for the benders are also different from the pots on the newer ones. I don't know on the older ones...

installed cc+

Michael Salmon [21030155]

got it done. it took me 30 minutes, it wasn't hard though i was nervous. on first boot though it said err 123, which i couldn't find anywhere. the cpu board was still up when i turned it on, so i lowered it down and plugged in the midi cord. it worked thereafter.

AWESOME to have midi finally. wowowowow.

great work guys!!

Michael Salmon [21030155]

installed cc+ - i spoke too soon.

well per my last email, the thing was working. even though i had the "err 123". then today i was just using it for the past 30 minutes, and it started to do some funky things.

  • it autotuned itself a bit too much
  • the foot sustain pedal worked backwards (ie depressed stopped sustain)
  • it would cut out for a blip occasionally (analog audio is what i noticed,maybe midi dropped too)
  • then it just STOPPED working
  • when i power it on, the LEDs blink as usual but for less them. then only the "up 1 oct" and "link lower" LEDs stay lit, everything else goes dark. nothing comes out.

oh crap. ideas? i guess ill open the case back and see if anything got disconnected next.

Jesper Ödemark [21010135]

Re: installed cc+ - i spoke too soon.


The "ERR123" means that the corresponding boards had trouble tuning. The autotuning sounds like the Chroma is struggling to get it right but doesn't manage it good enough. A calibration sounds like a good idea. I _think_ the foot pedal is a software setting. I think mine is like that too and has always been, just like the performance pitch control which is reversed.

If it's no software weirdness that David and Sandro might have an answer to I guess the "sudden death" is some grounding issue. Have you checked all your connections so nothing is loose, bent pins etc...?

Luca Sasdelli [21010226]

Re: installed cc+ - i spoke too soon.

Hi Michael,

in extent to what Jesper suggests, the sudden stop working could be caused by a PSU failure (the same scenario appeared to my Chroma just after CC+ upgrade); therefore, please check PSU voltages as per Hardware Fault Diagnosis & Repair: Checking the Power Supply Board.

David Clarke [21030085++]

Re: installed cc+ - i spoke too soon.

well per my last email, the thing was working. even though i had the "err 123". then todayi was just using it for the past 30 minutes, and it started to do some funky things...

Michael - as suggested by others, the main/first item to check/double check are the voltages coming from the power supply (per the values in the service manual).

A second item would be to make sure that the green ground wire that originally was connected to the rear panel (from the channel motherboard) was replaced and did get connected back up.

Going from there would be to ensure that the ribbon/flat flex cables connecting from the CPU board to the main I/O board are well connected. (Removing them and reseating certainly can't hurt).

Another test would be to place the original CPU back in to confirm that everything appear to be working properly with it present.

  • when i power it on, the LEDs blink as usual but for less them.

Less LEDs blink, or all the LEDs blink, but they blink fewer times than normal? (e.g., all the LEDs blink less than 16 times - or only a few LEDs blink - but those few blink 16 times?)

... then only the "up 1 oct" and "link lower" LEDs stay lit, everything else goes dark.

Does the system appear to otherwise be OK (i.e., does it change the number in the display when you press the panel buttons, etc.), or does it seem 'dead.'?

Michael Salmon [21030155]

Re: installed cc+ - i spoke too soon.

not sure if i have the skills to check the psu, i have a multimeter but im not skilled in it.

ill double check cable connects tomorrow to the cc+. ive heard lots about the psu dying so it seems like a strong possiblity, i guess ive just been too cautious about replacing it.

all blink for less time than normal, then only the two stay lit. the display is off the whole time.

ill get back tomorrow with more info..

Michael Salmon [21030155]

got it working

sorry forgot to report that i got mine working. i disconnected and reconnected everything. its been back to its old state, but with a working cc+ !


Jesper Ödemark [21010135]

Re: got it working

Congrat's and welcome to the club! :)

Power supply problems

Riku-Sakari Kujanen [21030858]

Hi group,

I'm new owner of Croma SN 21030858.

So far I have made all modifications to power supply by instructions of Martin Straw. I recapped it too. It had also some failed ICs in DCB and Stack Switch Board. (I mailed longer repair history to Chris Ryan few days ago [see registry entry for 21030858].)

Just when I tought everything was ok Chroma had its second opinion.

Supply runs ok without load, but under full load of output drops under 2.5 volts. I have tried to remove all DCBs and CPU Board, but the +5V Digital doesn't go any higher than 4.2 volts. Under full load (all boards attached) output is under 3 volts. Though the repairing supply has needed re-adjusting of R46 - always more and more. It did reached it's maximum before this. Before the readjust supply started to sag heavily. Sagging was slow random 1-2 volts pumpingand it was easy to see on scope.

I have looked all around but I don't see what is wrong. Before going the switching supply way have You any good ideas? I prefer to keep the old PSU because earlier investments to it (the big C3). Getting new Molex-connectors and suitable switching unit is bit hard and expensive here in Finland. And is this supply problem at all or is there something else failing?

Few measurements / facts:

  • Analog voltages are all ok.
  • Output from transformer is 18,25Vac / output. MR750 diodes are fine and rectified output is about 25 volts.
  • There is no Zener top of C3. (New cap is 47000u / 25V)
  • When supply was working everthing was ok. No random blinking or tapping etc.

How about bypassing the pre-regulator?

With suitable transformer analog circuitry is feeded by 2x 18Vac (or 36V CT) and +5V digital by 6Vac (or more) windings. This type tranformer is quite easy to find. I have proper hardware to mound about 100VA torroid to exactly same mounting holes of current transformer. Any comments about maximun voltage allowed to digital regulator? With pre-regulator maximum voltage in C3 is 7 volts. One volt causes about 3 watts of heat, so thermal stress wouldn't be so big issue. And there is one spare IRF531 device from the pre-regulator if more current is needed. Additional overvoltage protection cold be made crowbar style with SRC and zener.

Luca Sasdelli [21010226]

Hi Riku,

I suggest at first to measure the DC current on +5 dig, just to check if the voltage drop is due to an overcurrent or to PSU failure. About switching PSU, you can check some on-line resellers, because the average unit cost is quite low (here in Italy I've bought my MeanWell T-60 at around 30 euros + shipping).

Riku-Sakari Kujanen [21030858]

Stupid me - didn't measure analog voltages fully loaded: +5Va is low (about 3V) when under load. As reference to whole supply it caused the digital supply to fail. Noticed that The TIP29A has failed on analog supply. (No volts on emitter.) Seems like the usual suspect, "famous" digital regulator, distracted my attention totally.

Talking about bad luck. TIP29 was only transistor which I couldn't swap because none of local component supplyers didn't have it.

Thanks for feedback and good advice!

21010104 for sale

Totte K [21010104]

Have been playing the synth from new year, but now I allready have to sell it as I move and need money. I thought to ask from the list first. It seems very sturdy example. I thought something went wrong once but it was only fuse blown. So no issues with it, except one line of the LED display has dimmed, but it doesn't affect programming ease. I was thinking 2500e including insured shipping in europe, and packing by professional. The synth is in Helsinki. The flightcase is as heavy as the synth, so I don't think that's good idea to send. Very good packing sounds better to me. check the pictures from registry list. All selling ads have used the picture of my chroma but this is the real one :)

All the Best

Probing failed TTL chips and filter caps

Riku-Sakari Kujanen [21030858]

My quest to bring my Chroma back alive continues...

About week ago I mailed about powersupply problems which was after all caused "partial" short on i/o board. Do you have any ideas where to start?

Does TTL-chips fail to full short or just partially? Same goes for supply filtering caps? I measured resistance on between the supply lines DMM gives about 130R load. (about the same as CPU.) +5V digital goes down to 4.2 volts when all other boards are disconnected both i/o board and supply. The failure started gradually: Chroma did work for a while but then it started to draw more current and finally the supply went down. Is this symptom more cap or semiconductor kind or something else?



BTW: While reading all over again those schematics I started to think audio in mod trough noise circuitry. This seems so obvious it might already invented...?

It would be quite easy to remove other end of capacitor C14 or C15 on channel mother board, depending which type noise (white/pink) is more needed simultaneously with external audio. Noise signal from CMB is routed to input jack with switch which without plug connects noise signal back or audio signal to CMB and from there to all voice boards. It's possible to reuse the low level output jack which happens to be just right kind for this mod.

Before burning any DCBs etc, does this need somekind of extra circuirty, bufferig op amp perhaps?

David Clarke [21030085++]

... Does TTL-chips fail to full short or just partially? Same goes for supply filtering caps? ...

It is certainly possible for parts to get 'weak', and to draw different amounts of current - but that wouldn't necessarily be my first guess. Before going that route I'd perhaps suggest to see if you can measure the actual current draw to see if the boards are demanding more than the PSU should be able to supply (e.g., the ratings in the service manual), or if perhaps the draw is about correct, and that the PSU just can't keep up with the load...

Riku-Sakari Kujanen [21030858]

Thanks, David!

You were right about this - digital supply can't take the load. I measured current draw 0.51A (0.071V across 0.12R). It's way under 2,5A.

I noticed the diode pair CR24,25 on i/o board pulled the +5 analog down which pulls rest of supply voltages down. It might better to continue with dummy load so rest of the voltages are not loaded? When disconnecting CPU the analog voltage goes back up, but digital supply is still down around 4 volts but voltage on big C3 goes up to 6 volts. So pre regulator works ok?

Sorry about my silly diagnostics: I'm bit confused what is failing because all the electrolytics, transistors and opamps are replaced with new ones. Feels like I've made something wrong during first repair. I'm still hoping to fix up original PSU rather than swapping it because all the money and effort invested on this one. After all this problem can't be more than few parts.

David Clarke [21030085++]

... digital supply can't take the load. ...but voltage on big C3 goes up to 6 volts. So pre regulator works ok?

Do have an oscilloscope to see the waveform on the top of C3 under load? (the key item of interest will be not so much the average DC value - but the actual high/low points of the waveform .)

... I'm still hoping to fix up original PSU rather than swapping it because all the money and effort invested on this one. After all this problem can't be more than few parts.

I agree. There isn't that much in the circuit, so I would suggest that it is certainly worth-while to get the original supply running again.

Riku-Sakari Kujanen [21030858]

Plot thikens: I made simple 3 ohm load for testing PSU. Current draw is bit low 1.67 amps, but I'll think it's enough for testing purposes. The 5v analog supply is unloaded and it stays steady 5.05V. Same goes for both 12V rails.

On 30.5.2007, at 2.37, David Clarke wrote:

Do have an oscilloscope to see the waveform on the top of C3 under load? (the key item of interest will be not so much the average DC value - but the actual high/low points of the waveform .)

The pre regulator voltage collapses after all (due the low output). The waveform is shaped as is supposed, but it's kind of miniature of the normal. High point is 2.4 volts and low point 2.2 volts. Here's photo (5ms/div - 1V/div):

I loaded the pre regulator with same dummy load fitted on C3. Voltage on C3 raised up to normal level (appox 6 Volts) and the good old buzzing noise is back.

There is 12.5V on gate Q4 when output is under load, 9V when not loaded. This can't be right with voltage follower or is it? Failed Q4 perhaps or something else? Does the op amp drive higher voltages to gate of Q4 when output is low or is the current sensing circuitry acting too strong?

PSU connectors

Luca Sasdelli [21010226]

Hi all,

does anybody have the correct Brand and Part# of male power plugs soldered on the PSU board? I think they are manufactured by Molex, but I'm not sure about the product code.

Thanks for any help

David Clarke [21030085++]

The parts are from Molex.

The family of PCB-side connectors appears to be shown at: [URL has since become obsolete]

A 6-position connector, with all male pins appears as P/N 10-18-1061.

These are available on-line from Digikey and Mouser, and have a picture like:

If you didn't want/need a circuit-board mount version, then there are also panel-mount versions of similar connectors.

Luca Sasdelli [21010226]

Many thanks David,

quick and detailed ;-)

Manuals on eBay

Chris Ryan [21030691]

Performance Manual and Programming Manual in "very good condition." No bids yet. Ends May 31. Item #110131208997.

Picture from the auction:

midi moron report

Jesper Ödemark [21010135]

Hi List!

I guess noone has missed my attempts to control the Chroma via the CC+ and a Doepfer Drehbank. I had a hell of a time just getting the Drehbank programmed as I wanted since my own computer lacks midi out. A cheap joystick-port cable and my daughters old 166 MHz-machine helped out.

Now it's programmed like I want it too (behaving like it should from what I can sort out from the manual) and after some fiddling around with the setting inside the Chroma I get responses, not as intended necessarily, but still...

My conclusions is that I either programmed the Drehbank wrong or the Chroma isn't accepting the commands 'cause it only seems to recognise it's normal "realtime controllers", i e pitchbend, volume, hold etc. I also manage to send an autotune message from time to time though I cannot seem to repeat it intentionally.

I've read the CC+ manual again and again but I'm a real midi moron who is used to looking at knobs and seldom fiddles around with digital settings.

When I used the Pocket Dial it worked as it should on other controls so I guess this is a Drehbank issue/setting, but just in case it's not - Is there a setting the the Chroma which enables/disables CC-change messages other than the realtime controllers?

I hope I made sense...

David Clarke [21030085++]

...Is there a setting the the Chroma which enables/disables CC-change messages other than the realtime controllers?

Jesper - there are a couple settings which will make sense to check.

First, check the configuration setting for "Parameter Changes". Enter configuration mode by selecting [Set Split][36], and then select "6." You will want this setting "On."

Second, check that there is a mapping in effect. While in configuration mode, select P19 (Edit MCM) and confirm if you see parameters assigned. If no parameters are assigned, you may need to 'init' them. To do that, select "P20", and then move the data entry slider. You can then go back to P19 to confirm that the settings have been updated.

Jesper Ödemark [21010135]

Thanks for the heads-up...

I'll re-programmed the Drehbank yesterday and just _might_ have missed one thing last time. I had no time checking the new (?) programming though but will today. I'll also check the mentioned stuff below. I know I loaded the MCM 'cause I've configured the Drehbank to work with that.

Apart from the unintentional auto tune I performed a few times during the session I managed to "crash" the Chroma once. Everything went dead except the larger screen which just showed a big "4". I tried to re-do that again after a power off and on and never managed to do it again so I cannot explain the phenomenon. But I wanted to mention it if it means anything to you programmers. I know "four" and "death" is basically the same word in japanese but I don't think that's it. ;)

Jesper Ödemark [21010135]

Millions of thanks David!

It wasn't _just_ me being a midi moron, but yes, I had managed to fiddle with P6 in EP-mode too while trying out different settings. I have some filter in my master keyboard or maybe even a crappy midi lead that wasn't doing the job right. Now it kicks the famous butt! :-)

Some setting (like patch for example) sweep from 0-15 four times during a knob twist but there are settings in the Drehbank editor to fix that. Also, the writer of the drehbank program is a tech wiz but no pedagogic wiz. If anyone decide to go down the same road, do notice the differencies between save and store. It's not as obvious as you might think.

I thought loading my pre-prepared Chroma settings (yes, Chris, I'll gladly share if you want it) into the Drehbank via "save" was good since the midi indicator flashed etc. No luck... I tried loading them there via "store" instead. Same result... I re-read the read me file and realised that "save" puts a program in the RAM which is lost on power down (no PC in the studio so that sure was lost). "Store" didn't mean "saving and storing", it just meant taking whatever is in RAM and saving it on ROM. So my on/off-ing between sessions didn't help.

Now I've exposed my stupidity when it comes to these things, but it works. Off to some knob fiddling!

BTW - Chroma with kentonmidi for sale in Finland, 22000 SEK (circa 3000 USD/2400 EUR) here; I _think_ Totte (the seller) is on this list too?!

Chris Ryan [21030691]

BTW - Chroma with kentonmidi for sale in Finland, 22000 SEK (circa 3000 USD/2400 EUR) here; I _think_ Totte (the seller) is on this list too?!

Yes, he sent a message to the list on May 20; it is his 21010104 for sale.

Apple II Card on eBay

Chris Ryan [21030691]

For auction on eBay is an interface card for the Apple II. This is for use with the Fender Music System (see Playing the Rhodes Chroma with the Apple II Sequencer, Apple II Editors & Librarians: Fender Music System, and Syntech/Chroma Cult MIDI Kit: Manual: Using the Converter with the Fender Music System). I used to have one of these but it was stolen along with my Apple II+ in 1987.

From the description: "I have never tested it but all the components are there and it is in great condition. Sold as is." 1 bid, currently at US$10. Ends June 5. Item #130119425476.

Picture from the auction:

font used on chroma?

Jesper Ödemark [21010135]

Anyone knows? Chris maybe, who did the site?

Chris Ryan [21030691]

The font used on the Chroma is almost certainly Helvetica. The Rhodes logo is, I believe, a custom (or rare) variant of Bodoni.

On the site, I use a variety of fonts. The body is Lucida Grande, which is the default font on Mac OS X but not installed on most Windows systems (at least by default) so they get Verdana, Lucida, Arial, Helvetica in that order of preference. The left side navigation is Helvetica. See the main CSS file (chroma.css).

Chroma brass sound

Rob Belcher [16330123]


I remember reading that the brass sound at the beginning of Spandau Ballet's "True" was recorded with a Rhodes Chroma, is that right? I always thought it sounded like an Oberheim 4 voice or something! I always thought it was a great sound, is it a factory preset or something?

Paul Hackett-Evans [21010094]

Yes, it's true, Rob, it was a Chroma.

Roy Paynter did all their keyboard maintenance at the time. He was the UK's official Chroma engineer, he worked for Fender's distributor here. I read that Spandau Ballet had used the Chroma on their "True" and "Gold" albums and Roy confirmed this to me some time ago.

The only keyboards they used on the "True" album were a Chroma, a Fender Rhodes and an acoustic piano. There was a Prophet 5 in the studio control room whilst they were working on the album, but it was only used in working out arrangements. The band wanted a distinctive sound for their keyboards when recording "True". Everyone who was big in the UK pop scene at the time was using sounds from Prophet-5 (Orchestral Manoeuvres In The Dark, China Crisis, Japan), Jupiter 8 (Duran Duran, The Human League, Thomas Dolby) CS80 (Ultravox, John Foxx) and OB-Xa (Simple Minds, Re-Flex, Gary Numan). Spandau Ballet wanted something different. The Chroma was very new then and sounded like nothing else. It was just what Spandau Ballet wanted. Their use of the Chroma gave them a unique sound signature that set them apart from their contemporaries.

Their producers gave an interview when the album had hit big, in the now defunct UK-based magazine "International Musician", in which they said that the Chroma had a warmth and lushness to the sounds that matched the white soul of Spandau Ballet's song writing perfectly. The Chroma was the first synth to feature velocity sensitivity with a responsive, weighted keyboard. The expression this gave the synth was another big factor in Spandau's choice of the Chroma for their keyboard style.

The sound in the song "True" that you refer to is not a factory preset, it's something that Spandau's keyboard player and producers came up with themselves.

I've tried to reproduce it but haven't got it right yet. If I do, I'll post the sound to Chris to put on the site.

Incidentally, one of Roy's favourite stories from those days is of the time that Spandau Ballet returned from the European leg of their "True" tour in the mid-80s. They had asked Roy to meet their crew at the Airport to collect their stage keyboards (a couple of Chromas and a Moog of some type). He was to take them to his workshop to perform any maintenance that may have been necessary in the break before the band set off for the American leg of the tour.

Even though he was a big, strong Rugby player himself, Roy didn't relish having to move Chromas, as they are so heavy. But it was all part of the job.

Roy met the crew as arranged and an absolutely enormous, heavily-built roadie said he would get the Chromas for Roy. They went to the cargo area, where the roadie picked up a Chroma in its flight case as easily as if he were lifting a small briefcase. He swung the Chroma up in the air with one hand, balanced it on his shoulder and walked casually 400 metres to Roy's van, chatting to Roy as if there was no weight there at all, and gently lowered the Chroma into the van with one hand. Then he did the same with the other Chroma in its flight case. He didn't even break a sweat. Even now, Roy remembers this guy as the strongest man he'd ever seen.

Tom Klepacki [21030025]

Hi all, Good story about the weight of the Chroma with case.

My band and I flew from Tampa, Florida to New York in 1983 to record a song with producer/ engineer Don Casale (Iron Butterfly, Vanilla Fudge, etc.). I took my Chroma. I paid almost as much for air cargo for the Chroma, as I paid for my own ticket! THEN, I had to find a limo-van to take us all to Westbury, Long Island, to his studio. A taxi wouldn't have enough room.

I used my Chroma to track bass, strings, piano, pads, celeste, ...almost everything. Except for live drums and Strat. And vocals. The final mix, though almost all Chroma, sounded quite 'acoustic', and natural, for electronic circuits.

It's funny, though, that my Chroma seems to weigh twice as much now, as it did in 1983!

Mal Meehan [21010182++]

In fact, I own THE Spandau Ballet Chroma they used on the Live Aid gig, I'm guessing it's one of the two that Paul mentions below.

One thing that is strange about it is that there are 4 holes drilled each side of the vents in the top panel, probably to screw in a fan at some point... perhaps Roy might know something about this? It's currently at KSR restoration having an overhaul as she dies on me in a very big way, the PSU blew and took at the computer board and several voice cards. Depending on repair cost it may end up on the RLMusic website for sale shortly!

I bought it with all the patches intact and played it for about 8 months before she blew... sure wished I had dumped those patches just in case they were the original SB patches (it had been sitting in it's flight case for 20 years so they probably were the original Spandau Ballet patches).

This is the one in the registry that has had all serial numbers removed?

Go to next message in thread, June 2007

Factory sounds in wav format?

Heath Finnie [21030175]

Is there anyone who can send me some sound banks in wav format? (Doesn't have to be factory)

Thanks so much!

Chris Ryan [21030691]

You could use the Patch Conversion Tools to convert the sysex files (available on the Patch Downloads page) to .snd and go from there.

Heath Finnie [21030175]

Hi Chris,

The only issue is that I am very unfamiliar with terminal in MAC OSX...

Chris Ryan [21030691]

OK. Can anyone do a few conversions? If someone sends me the factory banks in audio format, I'll add them to the site.

I've actually been working on a Mac OS X GUI version of these; stay tuned.

Heath Finnie [21030175]

Thanks so much Chris!

Go to next message in thread, June 2007