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ChromaTalk Archives: May 2004

Expander on Ebay (again)

David Clarke [21030085++] · Wed, 05 May 2004 19:15:02 -0400

I see the expander (that was mentioned on the list in mid April) is up on Ebay again ... this time with a $995 starting bid (instead of $1,995).

(A little bit more reasonable - but still not a giveaway ...)

Olli [21010284] · Thu, 6 May 2004 20:28:35 +0200

hi david

could't find it.

best wishes

Newbie needs Chroma help

Ron Joseph [21030042+] · Thu, 06 May 2004 19:30:55 +0000

hello list,

I recently purchased a Chroma s/n 21030042 via E-bay. The unit displayed an error message upon start up:036. After reading the entire archive I new this meant that boards 0,3,and 6 failed the diagnostic. I turned off the machine and swapped the voice boards and got an error message with only 2 boards failing the diagnostic. On the third or 4 th power up the machine failed to turn on. I've still got a slight electric hum but no lights on the front panel. I've double checked all the connections I can see but still no go. Does anybody have any ideas? Unfortunately I'm not electonically inclined but I'm more than willing to learn although I think this probably isn't a newbie do it yourself project.I live in the Phila. Pa. area if anybody knows a Tech/store that does quality repair work.

For the record my machine is an older model with the white voice cards.There's a midi retrofit by syntech.It came with a ton off paperwork.(Most of this is probably already available on Chris's site but I'll gladly post it if not).Thanks in advance for the help....Ron Joseph

David Clarke [21030085++] · Thu, 06 May 2004 20:33:57 -0400

ron joseph wrote:

...On the third or 4 th power up the machine failed to turn on.I've still got a slight electric hum but no lights on the front panel. I've double checked all the connections I can see but still no go.Does anybody have any ideas?Unfortunately I'm not electonically inclined but I'm more than willing to learn although I think this probably isn't a newbie do it yourself project.I live in the Phila. Pa. area if anybody knows a Tech/store that does quality repair work.

Ron - welcome to the list (and to Chroma ownership).

Even if you can't find a good Tech/store nearby, if you happen to have a friend who's familiar with a multimeter/osciloscope (your favourite electrical engineering student, technologist or electronic hobbiest, etc.), you may be OK.

The Service Manual for the Chroma is available on-line. It is actually quite good, and insofar as electronics go - the Chroma is not too bad in terms of servicability.

If you happen to have a meter available yourself, the first/best/most likely thing to check first are the voltages coming from the power supply (there's a drawing at the back of the service manual showing what voltages should be available on what connectors).

Ron Joseph [21030042+] · Fri, 07 May 2004 01:50:00 +0000

Thanks David,

Part of the problem is I'm so new to the servicing aspect that I don't know what tools to buy (even to begin). Off to Radioshack tommorrow to buy a multimeter. Any other basic tools for a "Chroma toolbox"?Soldering Iron etc....rj

Chroma Pedal Set For Sale

John B. Rotondi [21030185+] · Sun, 16 May 2004 23:15:24 -0700

Hello Chroma Folks!

I just happened to spot this ad online at www.recycler.com, the online version of our local Recycler weekly trader magazine.

I thought some of you might be interested in this:

05/12 PEDAL set for Rhodes/Arp Chroma Keyboard. Three pedals. $50 OBO

[Ad contact info removed]

Chroma Expander D.O.A.

Wayne Griffin [16330111] · Tue, 18 May 2004 22:30:36 -0400

My Chromies,

I have just received an Expander (No. 111). After very carefully unpacking it, I carried it over to a stand, made the necessary connections (even used a protected AC outlet) and applied power to the machine.

All I got was the vibrating sound of the transformer inside the Expander. None of the LED's lit and neither displays came on- very frustrating after being assured the instrument was in top condition.

I connected the Expander to my mixer and heard from the audio output a buzzy, sawtooth-like wave with very prominent harsh upper harmonic. It didn't sound phasey like when you are playing a unison patch on a polysynth; it just merely sounded like a single, sawtooth with said shrill harmonic. My voltmeter has a freq counter on it and it said that the wave was about 120 cycles. I wonder if this is a harmonic of AC...

The only response from anything on the machine is the three band equalizer. You can hear the effect of the Bass, Mid and Treble sliders on the sawtooth wave that I mentioned. There is no response at all from Volume or Tune.

I am surmising that the Expander's power supply is blown. What are the chances that the power supply may have taken out other things downstream when it failed? I know that this Chroma lied dormant for no less than a year before I turned it on today- have any of you encountered this before?

David Clarke [21030085++] · Wed, 19 May 2004 19:34:55 -0400

I have just received an Expander (No. 111). ... All I got was the vibrating sound of the transformer inside the Expander. None of the LED's lit and neither displays came on- ...

Wayne - the audible hum at least tells you that the power supply is attempting to do something.

The general case of no LEDs/no Display is a general condition that will result if the main CPU didn't wake up properly (for whatever reason - bad power, bad connection, something else preventing the startup from progressing, etc.).

Since you do have a voltmeter I'd suggest:

  1. open the expander up, and inspect all connections (if the unit has been shipped recently, it is possible that a connector has shook loose).
    1. if all looks in place, take a quick peek around the batteries on the CPU board (just to make sure that a battery leak over the last year or so hasn't caused grief.)
    2. (while your hands are hovering over the CPU board, confirm the two ribbon connectors going to the CPU board are firmly attached.)
  3. use the voltmeter (and the service manual from the Chroma site) to confirm the proper output voltages from the power supply (+5V digital, +5V analog, +/-12) as they are seen at the power supply connectors.

Good luck in your mission!

(let us know how you make out)

Ron Joseph [21030042+] · Thu, 20 May 2004 02:24:03 +0000

Wayne,

I too had my Chroma die on arrival recently. I didn't plug in the Audio outs as I was trying to check error messages first. I received help from the list (Thank you everyone) and I'm now trying to learn enough about electronics to fix the power supply. There was a great article on a different power supply project entitled "Nuclear powered Chroma". Does the expander have the same power supply as the keyboard version? If so,maybe that would help. good luck....Ron Joseph

Wayne Griffin [16330111] · Thu, 20 May 2004 2:56:27 -0400

Wayne - the audible hum at least tells you that the power supply is attempting to do something.

As an experiment, I removed all the voice cards and the power connection to the EQ boards. As a result I got some more visible flickering from the LED's and a few dim squigglies from the data readouts.

Are there any problems with applying power to the various boards, even with the voltage out of spec?

Upon disconnecting P1, P2 and P3 from the power supply the very prominent 60 Hz hum/vibration went away. I began to read some voltages out on the connectors, but my tired hand slipped and I blew out the fuse as I shorted something though before that happened, I did get some interesting readings. I found 5.05V, +12 and -12- but I also found voltages like 25V and 2.1V...are those normal? Mind ye that none of these are with any of the 4-5 boards connected.

As a general electronics question- can one measure any voltage on the supply accurately even if a board or boards aren't connected to it? Doesn't that affect the load on the power supply?

I have a small board of some sort with a chip marked F7412PC that is wired into 4 different places on the I/O board (there is one rather long lead that goes to the ADC0809CCN, Z3) I was wondering what this board might be. I found a hideously cold solder joint on this wire that fell off Z3 when I touched it gently. I will resolder that connection no doubt before powering back up again.

I verified the ribbons between I/O and CPU and most I was able to trace out. On P9 of the CPU board, are there supposed to be punctures through any of the traces inside the ribbon?

Is there any chance of stressing the boards (in particular the I/O board) when trying to detach these Molex bits?

Though there were some old corroded Energizer AA's in there that were so old there was no year stamp on them I saw no damage fortunately to the PCB.

How are the EPROM's for the Expander different from the Chroma? Mine are labeled Expand C0 R14 (Z29), Expand C8 R14 (Z30), Expand D0 R14 (Z31), Expand D8 R14 (Z32), Expand E0 R14 (Z33), Expand E8 R14 (Z34), Expand F0 R14 (Z35), Expand F8 R14 (Z36)... are these the most current versions of the Rom?

I just want to say that without this site and those who chromatalk, I would never have sought to own one of these machines, thanks. [w]

Doug Terrebonne [21030114] · Thu, 20 May 2004 00:19:44 -0700 (PDT)

--- Wayne Griffin wrote:

Though there were some old corroded Energizer AA's in there that were so old there was no year stamp on them I saw no damage fortunately to the PCB.

This could be really bad news I'm afraid since you can't just tell by looking. Battery acid is nasty stuff... I spent over 2 years trying in vain to repair a Chroma CPU board where the batteries leaked all over damaging lots of chips, circuit traces, etc...

Olli [21010284] · Thu, 20 May 2004 09:44:32 +0200

hi wayne! wellcome. i went through some probs as well when i got my chroma and got them fixed with the help of list members. so odds are in your favour!

As an experiment, I removed all the voice cards and the power connection to the EQ boards. As a result I got some more visible flickering from the LED's and a few dim squigglies from the data readouts.

well, if you got some flickering, maybe thethe main condensator needs replacement as it may indicate a lack of stability of the voltage, which could explain partly some of the hum.

Are there any problems with applying power to the various boards, even with the voltage out of spec?

if voltage too low, don't think so.

Upon disconnecting P1, P2 and P3 from the power supply the very prominent 60 Hz hum/vibration went away. I began to read some voltages out on the connectors, but my tired hand slipped and I blew out the fuse as I shorted something though before that happened, I did get some interesting readings. I found 5.05V, +12 and -12- but I also found voltages like 25V and 2.1V...

that is strange. i don't think these are normal. where did you measure them?

are those normal? Mind ye that none of these are with any of the 4-5 boards connected.

As a general electronics question- can one measure any voltage on the supply accurately even if a board or boards aren't connected to it? Doesn't that affect the load on the power supply?

it does but i don't think that is does influence the voltage in a measurable way. other than that you might blow parts of the circuit if you remove some or all of the DCBs.

I have a small board of some sort with a chip marked F7412PC that is wired into 4 different places on the I/O board (there is one rather long lead that goes to the ADC0809CCN, Z3) I was wondering what this board might be. I found a hideously cold solder joint on this wire that fell off Z3 when I touched it gently. I will resolder that connection no doubt before powering back up again.

if i recall correctly that was some sort of a bug-fix on the board. it should definately be connected properly.

I verified the ribbons between I/O and CPU and most I was able to trace out. On P9 of the CPU board, are there supposed to be punctures through any of the traces inside the ribbon?

punctures? i don't think so. of what kind?

Is there any chance of stressing the boards (in particular the I/O board) when trying to detach these Molex bits?

do it very carefully.

Though there were some old corroded Energizer AA's in there that were so old there was no year stamp on them I saw no damage fortunately to the PCB.

uffff! :-)

How are the EPROM's for the Expander different from the Chroma? Mine are labeled Expand C0 R14 (Z29), Expand C8 R14 (Z30), Expand D0 R14 (Z31), Expand D8 R14 (Z32), Expand E0 R14 (Z33), Expand E8 R14 (Z34), Expand F0 R14 (Z35), Expand F8 R14 (Z36)... are these the most current versions of the Rom?

I just want to say that without this site and those who chromatalk, I would never have sought to own one of these machines, thanks. [w]

yes, very helpful! good luck.

olli

David Clarke [21030085++] · Tue, 25 May 2004 19:13:33 -0400

As long as things are in the right vicinity of the correct value - the parts shouldn't be damaged. (On the pessimistic side, even if the values are way outside of where they should be - if damage was going to occur it probably already has happened - so having it powered up long enough to check the PSU probably won't hurt more.)

Upon disconnecting P1, P2 and P3 from the power supply... I found 5.05V, +12 and -12- but I also found voltages like 25V and 2.1V...are those normal?

Figure 3-5 from the Service Manual is a good reference to use. It will tell you some good places to measure, as well as give you the ball park values of what to expect.

The 5.05V, +12 and -12 all sound good.

Even the 25V is probably OK, as this is the general voltage that would be used by the Tapper.

I have a small board of some sort with a chip marked F7412PC that is wired into 4 different places on the I/O board (there is one rather long lead that goes to the ADC0809CCN, Z3) I was wondering what this board might be.

The general circuit involved here is discussed/described in Field Change Notice FCN2-004 - it is the implementation for the End-of-Conversion (EOC) indication.

On P9 of the CPU board, are there supposed to be punctures through any of the traces inside the ribbon?

No. The cables should be 1:1 from side to side. In general, the cable should look complete and clean, similar to the picture in David Clarke's post of December 15, 2003 (albeit with a black shroud on the I/O board end.)

Is there any chance of stressing the boards (in particular the I/O board) when trying to detach these Molex bits?

The big power supply molex connectors can be stiff, but a little bit of wiggling should allow you to safely pull them out.

Though there were some old corroded Energizer... ... If I were to post some high res pictures of my cpu board, do you think anyone would be able to see anything? I don't see immediately any damage, but that's not to say there isn't any there. cheers, [w]

If the solder connections near-by look nice and shiny (as opposed to a very dull grey), you're probably OK.

I would be more concerned about the ribbon cables noted above. The way the CPU board goes into the Expander the edge of the P10 ribbon seems a bit susceptible to battery damage (the physical installation is such that a leaking battery will drip on the side wood 'floor'. The P10 cable also rubs on this same piece of wood. Of course, if the Expander had been store by sitting it on its end, the batteries could have dripped on P9.

How are the EPROM's for the Expander different from the Chroma?

Actually - they're almost the same.

The Rev 14 chips you have would reflect the most current released version of firmware.

In general I'd recommend:

Check out the ribbon connector, reattach the wire to Z3, replace the fuse, connect back up the PS connectors and with the voice cards removed, attempt to repower the keyboard.

Once powered up, measure the voltage at J1, J2 and J3 of the Power Supply to see what sorts of voltages are present (you can slide the multimeter tip right into the backshells of the J1, J2, J3 connectors).

If the voltages look fine, then we'd need to dig a bit.

If one or more of the voltages look bad, then we could selectively remove J1, J2, J3 or J4 to see if one particular board (or set of boards) is 'making' the rail bad - or if it is the supply itself.

David

Joyn Leimseider [21030434++] · Wed, 26 May 2004 08:35:08 -0600

My first guess is that the 3 volts is a bad reset, caused by the 2 bad yellow 3.3 microfarad electrolytics. Replace those and see if it's all OK.

Wayne Griffin [16330111] · Sat, 29 May 2004 4:28:17 -0400

My CHROMANS,

I have been reading some of the chromatalk archives and trying to glean as much as possible from them before potentially asking about a topic that's already been covered.

Anyhow, I will eventually submit to the Chroma Registry. Ideally, I would like to have my unit operational before formally accounting for it- which is completely irrational and entirely out of certain emotions I have for this machine.

Do have a gander at me picture. I am uncertain of the validity of this question, however, I know that you all will be kind to me :)

Can you see the "off-board" Z4 that is supposed to correspond to the digital rectifier's pre-regulator circuit? I don't see it. Is there not supposed to be something lodged between the electrodes of the giant C3?

This picture was taken as I first opened the machine. The only mod that was apparent about my Expander was the that it arrived with a syntech interface already installed.

Were Expander power supplies any different?

Puzzled,

Wayne Griffin

David Clarke [21030085++] · Sat, 29 May 2004 10:41:59 -0400

Do have a gander at me picture. ... Can you see the "off-board" Z4 that is supposed to correspond to the digital rectifier's pre-regulator circuit?

It truly looks MIA.

Is there not supposed to be something lodged between the electrodes of the giant C3?

Yes, exactly. Here is a picture (of an Expander PSU, from a similar vantage point as yours) showing the little circuit board with Z4 installed.

Were Expander power supplies any different?

The Chroma and Expander supplies are identical - the only difference at all would be the serial number

Dave

Wayne Griffin [16330111] · Sat, 29 May 2004 20:08:56 -0400

Chroma Expander D.O.A. (Z4 M.I.A.)

Well dudes... What the heck am I supposed to do now?

sincerely,

Wayne Griffin

PS- I had to rewrite this note 4 times to remove all the cussing :)

Doug Terrebonne [21030114] · Sat, 29 May 2004 17:44:28 -0700 (PDT)

Take it to a tech? By the way, can we stop sending big attachments to the list? Some of us have a mailbox size limit... :-(

Thanks,
Doug

David Clarke [21030085++] · Sat, 29 May 2004 22:18:12 -0400

Well dudes... What the heck am I supposed to do now?

The part itself is still available (take a peek in the ChromaTalk archives for discussions about it being available from parts brokers, etc.)

In addition, you might just luck out. Different folks out there have gone and swapped out the original Chroma PSU for a replacement switching power supply. I would assume that means that they still have the guts for the original supply kicking around (and hence might be willing to part it out).

Yet another alternative might be to go the route of the Power Supply replacement.

Joyn Leimseider [21030434++] · Mon, 31 May 2004 08:22:46 -0600

It will work perfectly without it. It's only there to protect the filter cap. If you really want to replace it, you can get them from MusicTek Services in N. Hollywood, Ca. The number is 818 506-4055. I don't recommend replacing it. It's totally unneccessary, particularly if you replace the main filter cap with the current 15 volt replacement. J.L.

Go to next message in thread (July 2004)

CPU board battery leakage - pictures

Wayne Griffin [16330111] · Thu, 20 May 2004 3:30:27 -0400

If I were to post some high res pictures of my cpu board, do you think anyone would be able to see anything? I don't see immediately any damage, but that's not to say there isn't any there. cheers, [w]

Rich Hilleman [21030351+] · Thu, 20 May 2004 12:11:16 EDT

You need to pull board and test each tracing for continuity. Next you need to continuity test the parallel traces (on both sides) to make sure the the acid flow didn't leave iron oxide under the board surface. I works as a great trace short.

I hope it comes out ok. Sorry you have to go through this. There are a lot of dead PolySixes out there with the same problem.

Chroma dcb scaling problem

Arti Haroutunian [21030388] · Wed, 26 May 2004 11:52:20 -0600

I have two dcb's in which one channel won't scale properly. Using patch 1 near middle C both channels sound in unison, but when going to either extreme of the keyboard one of the channels goes out of tune. On the highest note one channel is about one note to high, and on the lower end the same channel is one note too low. The other channel is fine. The instrument is able to tune the dcb's.

Power supply is good, the other six dcb's work perfectly. I've replaced Z4 with no change. Problem doesn't change over time, after leaving instrument turned on overnight the behaviour hadn't changed. Tempco's and transistor arrays measure fine. SH pitch voltages are uniform for both channels.

So obviously something is going bad in the expo converter, but what?

Any hints would be greatly appreciated.

Olli [21010284] · Wed, 26 May 2004 20:42:57 +0200

what about the capacitors? sounds to me as if one might not hold its nominal current capacity driving an osc out of tune?

Olli [21010284] · Wed, 26 May 2004 21:00:54 +0200

sorry forget that i didn't read the problem properly. of course it may be a CMB problem. but be sure to check its not the molex connectors of the DCBs. it took me several changed chips to discover that two of these were broken on two DCBs so changing components won't help.

David Clarke [21030085++] · Thu, 27 May 2004 20:02:34 -0400

I have two dcb's in which one channel won't scale properly. ...

I can only guess that there's got to be something we're missing, in that if the channels are that far out, they should fail the auto-tune.

  1. Can you confirm that the problem follows the channel cards themselves (i.e., if you remove all the cards, only leaving in one of the 'problem' ones, does the problem occur regardless of which slot the cards are in?)
  2. Is there any change in observed behaviour if the 'scratch patch' is used for the testing?
  3. Can you confirm that when the Chroma first powers up it flashes all the LEDs 16 times (and it takes approx 7 seconds to completely boot?

Arti Haroutunian [21030388] · Thu, 27 May 2004 18:49:16 -0600

Thanks for your responses.

what about the capacitors? sounds to me as if one might not hold its nominal current capacity driving an osc out of tune?

Checked the caps in and around the expo converters and they checked good. Replaced them anyway for one channel with no change.

.....but be sure to check its not the molex connectors of the DCBs.

Did a visual and electrical test, all good.

  1. Can you confirm that the problem follows the channel cards themselves (i.e., if you remove all the cards, only leaving in one of the 'problem' ones, does the problem occur regardless of which slot the cards are in?)

Slot positioning and/or existence of other cards does not affect the problem.

  1. Is there any change in observed behaviour if the 'scratch patch' is used for the testing?

None

  1. Can you confirm that when the Chroma first powers up it flashes all the LEDs 16 times (and it takes approx 7 seconds to completely boot?

Actually only one of my two bad cards passed tuning. So with all of my cards installed I get 14 flashes, one of the bad cards gets locked out but the second one does get enabled.

Additionally I checked tuning on the bad card that passes the chroma test. Using Split 26/27 I respectively disabled channels a/b and hooked up a chromatic tuner. Channel A was perfect, channel B was a semitone too low at the lowest note, a semitone too high at the highest note and dead on at middle C. The other bad card displayed similar behaviour, but at least that one doesn't pass the tuning test.

Maybe it's time for some industrial strength deflux.

Arti

David Clarke [21030085++] · Sat, 29 May 2004 12:06:20 -0400

Checked the caps in and around the expo converters and they checked good.

The other caps to possibly take a peek at are those in the Sample and Hold section. Specifically, it might be worth-while looking at the voltages coming out of the buffer amplifiers from the sample and hold section to see if there is any undo droop for the control voltages for the VCO/VCF.

Actually only one of my two bad cards passed tuning. So with all of my cards installed I get 14 flashes, one of the bad cards gets locked out but the second one does get enabled.

Set Split 31 might also help to identify the problems - esp. the one that fails auto-tune. You can have the board enabled, and then do an A/B comparison between its on-card voltages/signals vs. a good card.

Good luck.