ChromaTalk Archives: September 2008
- Synthesizer Magazin Article and Audio
- Re: Chroma on german Ebay (3)
- CC+ 5th batch (repost) (2)
- Re: Power supply surge suppressor sub.
- Chroma power supply (7)
- filterpedal and midi (3)
- Resurrecting a Chroma (15)
- Chemical Contact Enhancer
Synthesizer Magazin Article and Audio
Chris Ryan [21030691] · Tue, 2 Sep 2008 22:00:15 -0700
This month's addition to the site is the article "Fender Rhodes Chroma" from the May-June 2008 issue of Synthesizer Magazin. Christian Kleine [21030210] kindly translated the article from the original German to English. It's an entertaining read, and four audio demos are included.
Re: Chroma on german Ebay
Go to first message in thread, August 2008
Michael Zacherl [21030253] · Wed, 3 Sep 2008 10:55:42 +0200
Just out of curiosity I checked back to this item and read:
"Der Verkäufer hat diese Auktion vorzeitig beendet, da der Artikel zerstört wurde und daher nicht mehr verkauft werden kann."
which translates on the US-ebay site to (roughly!):
"The seller ended this listing early because the item was lost or broken."
Huh? What's going on?
Jesper Ödemark [21010135] · Wed, 03 Sep 2008 11:56:58 +0200
I bet he got an offer off-Ebay and sold it there. It's common, at least in Europe. He might even have sold it on another site...
Christian Kleine [21030210] · Wed, 03 Sep 2008 14:30:52 +0200
This is the standard phrase on ebay germany if an auction is prematurely cancelled by the seller. Possibly he decided to keep it or he got an irresistible offer...
CC+ 5th batch (repost)
Sandro Sfregola [21010294] · Wed, 3 Sep 2008 23:22:20 +0100
(This message has already been posted on August 13, 2008.)
We have once again placed enough people on the CC+ 'wait list' to justify another build of boards.
We propose to accept orders for this fifth build up until Saturday, September 14th (midnight, Eastern Time).
To ensure a timely order of parts for those who have requested CC+ boards, we would like to receive payment by Saturday, September 21st.
Within September 7th we will be individually getting back in touch with the people on the wait list to see if you're still interested - and if so, to confirm your order. [David will be contacting the people from North, central and south America, Australia, China, Japan and Sandro will be contacting the people from Europe, Africa, Middle East.]
If you're not currently on the wait list - but would like to have a board from the 5th build - please be sure to get in touch before September 14th.
If you believe you're on the wait list but have not received an e-mail from either Sandro or David within September 7th - be sure to let them know.
Once again, thank you for your continued interest and participation.
Robert Shanks [21030301] · Thu, 4 Sep 2008 15:01:40 -0400
Sandro, David,
Please include me on the waiting list. Thanks
Re: Power supply surge suppressor sub.
Go to first message in thread, August 2008
John Leimseider [21030434++] · Mon, 8 Sep 2008 09:30:49 -0600
I have about 50 of the originals in stock if anyone needs any...
Chroma power supply
Malte Rogacki [21010091] · Sat, 13 Sep 2008 22:49:21 +0200
Hello everybody;
after several years (!) I finally got my Chroma back - unrepaired of course; and during the shipping back the data entry slider was broken off.
So, to get things rolling: I'm having power supply issues (probably a number of faulty voice cards as well, but first things first).
Symptom: No 5V digital.
With P2/J2 not connected I get on powerup voltage rising up to appr. 7V on top of C3 and then immediately breaking down to 1.8V. I guess that's the overvoltage protector kicking in? I'm also guessing that this means the preregulator isn't working properly (is biased too high)? Or is this normal behaviour without the proper load?
With P2/J2 connected I'm getting 1V on top of C3. If I'm interpreting the service manual correctly this means there is a short somewhere, right?
Any ideas? I guess I *could* spring for an SPSU but I'm eager to learn a bit by trying to fix the current state first.
Luca Sasdelli [21010226] · Sun, 14 Sep 2008 00:02:49 +0200
Hi Malte,
the preregulator is linear type, so you shouldn't have problems without load; perhaps this could be a current issue, and the regulator cannot supply enough current to load, thus dropping the voltage instead.
The voltage drop on C3 is a frequent issue, generally caused by the protector itself, but it can be the capacitor with some current drain inside too; you should provide a new capacitor and a new protector to test it: I don't know if this is a good choice indeed.
If you like to try fixing PSU by yourself, first prepare a dummy load to connect to the PSU instead of the instrument, so you can try all you like, without hurting the Chroma. With the dummy load, arranged with some known value power resistors, you can simulate the right current drain and therefore to have the PSU working in its ideal conditions.
Here you'll find useful data: Upgrading the Rhodes Chroma Power Supply.
David Clarke [21030085++] · Sun, 14 Sep 2008 11:23:33 -0400
Malte Rogacki wrote:
With P2/J2 not connected I get on powerup voltage rising up to appr. 7V on top of C3 and then immediately breaking down to 1.8V. ... With P2/J2 connected I'm getting 1V on top of C3. If I'm interpreting the service manual correctly this means there is a short somewhere, right?
I agree with Luca that the two most likely problem areas are the big capacitor and the overvoltage protector.
You had mentioned disconnecting P2/J2 - but +5V digital also goes out J3 to the channel mother board.
I'd suggest also disconnect J3 to rule out problems elsewhere affecting the supply.
If you still see the big drop without any load - I would suggest temporarily removing the protection board from the top of C3 and re-measure. If the voltage now looks OK, then that points to a failed Z4.
If the measurements were taken with a volt-meter, it would be recommended to also look at them with an oscilloscope (if one is available). This will let you know if the 7V (or 1.8) is actually a good steady level - or if that is just the average of a huge ripple on the supply (e.g., C3 not storing anything and needing to be replaced).
If C3 is still the light-blue Mallory original - then it is recommended that it be replaced anyway (especially given that they're not too expensive, and always get weak over time).
Malte Rogacki [21010091] · Mon, 15 Sep 2008 21:54:12 +0200
Thanks for all the comments and hints.
Update:
Q3 was the culprit. Voltage to C3 was about 15V; no wonder that the overvoltage protector was becoming active (after all, that's what its job is). The power supply is more or less working now.
Note: Without any load the voltage on top of C3 gets up to around 7.2V which is about the voltage where the protector becomes active. Under load it's significantly lower (and almost within the limits described in the service manual). I guess that's normal?
My power supply is one without the R46 potentiometer; I'm thinking about adding this one (and of course changing R3). Any ideas about this?
Malte Rogacki [21010091] · Wed, 17 Sep 2008 00:45:54 +0200
Power supply/IO board woes
Hello everybody;
I'm making (slow) progress in bringing back my Chroma from the dead.
The power supply works by itself pretty well. The Chroma powers up (ok, most of the time); however it doesn't manage to tune a single voice. So far I've found the following behaviour:
With the IO-board connected the +/-12 volts drop to around 6 volts each. Removing the power connector restores them to around 12.40 volts. So I suspect the Channel Mother Board and the EQ Board are not responsible for this.
As far as I can see the only two other connectors that carry +/-12 volts from the IO board are J20 and J13 (and of course J22 which is unused anyway). Unplugging J20 and J13 doesn't change anything; the voltage drop still happens.
So I assume that there must be something wrong with the IO board itself. Given the small number of chips that actually use the +/-12 volts I don't suspect the power supply itself here.
So I guess it's chip swapping, right? Or could this be anything else (I've already checked C1 and C3 on the IO board). Is it a good idea to swap the 1458/4558 for chips with better specs?
Leonardo Ascarrunz [no serial number] · Wed, 17 Sep 2008 13:05:54 -0600
Re: Power supply/IO board woes
My advice is to replace the entire power supply with a stable switching supply. Not doing so is simply a waste of time and money. A new switching supply is about 50 US dollars. Once the new supply is in you can start troubleshooting.
David Clarke [21030085++] · Wed, 17 Sep 2008 19:56:36 -0400
My power supply is one without the R46 potentiometer; I'm thinking about adding this one (and of course changing R3). Any ideas about this?
If it were me, I'm not sure I'd bother going through the effort to actually install the potentiometer.
For the number of times over the life of the power supply that it would need to be adjusted, I'd suggest using the procedure noted in the service manual (e.g., adding a component in parallel to adjust the voltage, as needed).
(Just my opinion.)
filterpedal and midi
Claes von Heijne[16330008] · Mon, 15 Sep 2008 15:05:08 +0000
I have installed the CC+ and SPSU in both my Chroma and Expander, and just used them on a recording. Great sounding, thank you, Sandro and Luca. However I had a problem, and maybe somebody on the list has an idea? I use the original volumepedal hooked to pedal 1 input on the Chroma, programmed to open the filter, and send the midi-cc-info to the Expander and further, where I for a while had a Korg R3 Vocoder. Sometimes the midiinformation seems to be much for the Expander, it starts to rumble, or reboot. Also the R3 got too much info and started to rumble. I work the filter up and down quite a bit with pedal, but isn't this meant to be possible, or is the much, or is something wrong?
Sandro Sfregola [21010294] · Tue, 16 Sep 2008 19:59:09 +0100
Claes, there is nothing wrong in your setup: you have discovered a firmware bug.
David and I are aware of this problem and we are working to fix it in the next firmware release. The bug regards only the TX portion of the CC+ MIDI interface while using continuous controllers.
Technically speaking, the problem can be described as follow:
The standard MIDI interface hardware is capable of a maximum data rate of about 3125 bytes per second; when you use controllers, a lot of data are generated and sent to the MIDI OUT; there is a data buffer of FIFO type (First In First Out) that fills when there is a momentary volume "peak" in the data stream; while playing the Chroma doing a "wild" use of controllers, occasionally the TX FIFO overflows and erroneous data are transmitted (the "rumble" that you experienced are actually note on messages sent as CC data).
In the meantime, please check your pedal (s): be sure that the connection to the Chroma is good and the pot inside is clean; noise can lead to the generation of unwanted controller data.
Also, check the two lever controllers on the left side of the Chroma: pots must be free from noise and the connections solid.
Michael Zacherl [21030253] · Tue, 23 Sep 2008 09:26:31 +0200
midi via usb?
Technically speaking, the problem can be described as follow:
The standard MIDI interface hardware is capable of a maximum data rate of about 3125 bytes per second; when you use controllers, a lot of data are generated and sent to the MIDI OUT; there is a data buffer of FIFO type (First In First Out) that fills when there is a momentary volume "peak" in the data stream; while playing the Chroma doing a "wild" use of controllers, occasionally the TX FIFO overflows and erroneous data are transmitted (the "rumble" that you experienced are actually note on messages sent as CC data).
This has just drawn my attention:
When designing the CC+, you and David did you consider incorporating an USB interface, probably as an add-on? I just had the picture using Pure Data as controlling entity generating lots of data. The traditional MIDI interface certainly would gain some hiccups given the possible density of data. Saying that I'm not sure if the 63C09 could handle that load anyway?!
Just a thought, :-) Michael.
Resurrecting a Chroma
Michael Grossman [21030350] · Sun, 21 Sep 2008 00:33:51 -0700
I am the proud owner of a broken Chroma. This is what I have done so far. When I got her home I discovered the fuse was missing and after replacing it the voltages were about half of what they should be. Disconnected everything from the power supply and with the exception of digital +5V all voltages were good. After reading through the forum I tried removing the crowbar circuit and voila the digital +5V also looked good. Not so fast. Connected everything and the digital +5V was again too low. Figuring the filter cap must be bad I went to the surplus electronics store and found a 65000uF 25V cap and decided it was a reasonable substitution. As it was taller I mounted it on its side and when I fired up the unit all was well except the reset was toggling at 120Hz. After another trip to the surplus store I started replacing components in the reset circuit. Turns out C12 was what fixed it. Powered her up and saw blinking lights but unfortunately no 7-segment display and the Chroma was unresponsive. Spent quite a while analyzing the CPUs and since there had been battery leakage sometime in the past eventually I found one of the 2716 socket pins had become corroded and was not making contact. I did replace the 68B09, RAM and all socketed 374s along the way though it was probably unnecessary (at least I have spares). The Chroma now boots and makes some sounds though it displays err 026. I assume that means voice cards 0, 2 and 6 cannot be tuned well enough. The unit has the Chromaface installed but my understanding is it does not support sysex so I hooked up a laptop and was able to get a factory bank to load through the cassette interface. Now here is where things stand. Though I can select any one of 50 presets (proving the memebrane is sound) when I try to edit parameters many of the keys map to the same one. Unlike the presets one cannot select all 50 parameters to edit. My current theory is one of the 2716 eproms is bad and it executing bogus code when editing parameters but generally works otherwise. Does this theory make sense? Any alternatives?
P.S. Sorry for the long winded tirad but I thought documenting my experiences might help someone else.
David Clarke [21030085++] · Sun, 21 Sep 2008 10:50:21 -0400
Mike - your debug log is good to have on file with the list, as the steps taken and the observations seen (for the Power Supply) cover off a good majority of the problems that crop up.
... The Chroma now boots and makes some sounds though it displays err 026. I assume that means voice cards 0, 2 and 6 cannot be tuned well enough.
Yes. Correct.
when I try to edit parameters many of the keys map to the same one. Unlike the presets one cannot select all 50 parameters to edit. My current theory is one of the 2716 eproms is bad and it executing bogus code when editing parameters but generally works otherwise. Does this theory make sense? Any alternatives?
If you saw battery residue on/near the EPROMs, then it is indeed possible that one has been affected.
The EPROM images are available on-line and so if you have a programmer it would be a good check to at least confirm that the contents of the proms do successfully check against the intended images. If they do not - then there is a problem expected.
If the EPROMs check out, then if you perhaps share the patterns seen, we might be able to make better recommendations (e.g., selecting P1 -> P5 always returns P1, selecting P6-P9 always returns P10, etc. Details of what is/isn't seen in the small display and the 4 LEDs in the Panel Mode section).
P.S. If you have not done so already, it would be good to send your Serial Number data along to Chris Ryan for inclusion in the Chroma Registry.
Leonardo Ascarrunz [no serial number] · Sun, 21 Sep 2008 11:26:24 -0600
Try replacing the strobe switch matrix strobe decoder on the I/O board (z15). If that chip is not working then the membrane switches will not be scanned properly.
Michael Grossman [21030350] · Sun, 21 Sep 2008 11:40:43 -0700
I forgot to mention in the previous post there are many keys that either do not sound or stick. I assume a thorough cleaning is what is needed. Any recommendations?
Here is more information on the parameter mappings:
After setting up the "scratch" patch (Press Edit A/B together then Hold Param Select and hit 1-50)
Interesting quirk is: Switches that are a multiple of 4 toggle between the current value and previous value when the switch is repeatedly pushed.
- Selecting P1 returns L0 (or L7) 0
- Selecting P2 returns P3 0
- Selecting P3 returns L0 (or L7) 0
- Selecting P4 returns P4 0 (toggles between P4 0 and P3 0)
- Selecting P5 returns P4 0
- Selecting P6 returns P7 0
- Selecting P7 returns P4 0
- Selecting P8 returns P8 0 (toggles between P8 0 and P7 0)
- Selecting P9 returns P8 0
- Selecting P10 returns P11 0
- Selecting P11 returns P8 0
- Selecting P12 returns P12 0
- Selecting P13 returns P12 0 (toggles between P12 0 and P11 0)
- Selecting P14 returns P15 0
- Selecting P15 returns P12 0
- Selecting P16 returns P16 31 (toggles between P16 0 and P15 0)
- Selecting P17 returns P16 31
- Selecting P18 returns P19 0
- Selecting P19 returns P16 31
- Selecting P20 returns P20 0 (toggles between P20 0 and P19 0)
- Selecting P21 returns P20 0
- Selecting P22 returns P23 31
- Selecting P23 returns P20 0
- Selecting P24 returns P24 0
- Selecting P25 returns P24 0 (toggles between P24 0 and P23 0)
- Selecting P26 returns P27 0
- Selecting P27 returns P24 0
- Selecting P28 returns P28 0 (toggles between P28 0 and P27 0)
- Selecting P29 returns P28 0
- Selecting P30 returns P31 0
- Selecting P31 returns P28 0
- Selecting P32 returns P32 0 (toggles between P32 0 and P31 0)
- Selecting P33 returns P32 0
- Selecting P34 returns P35 0
- Selecting P35 returns P32 0
- Selecting P36 returns P32 0 (toggles between P36 0 and P35 0)
- Selecting P37 returns P36 0
- Selecting P38 returns P39 63
- Selecting P39 returns P36 0
- Selecting P40 returns P40 0 (toggles between P40 0 and P39 0)
- Selecting P41 returns P40 0
- Selecting P42 returns P43 0
- Selecting P43 returns P40 0
- Selecting P44 returns P44 0 (toggles between P44 0 and P43 0)
- Selecting P45 returns P44 0
- Selecting P46 returns P47 15
- Selecting P47 returns P44 0
- Selecting P48 returns P48 0 (toggles between P48 0 and P47 0)
- Selecting P49 returns P48 0
- Selecting P50 returns L0 0 (or L7)
Michael Grossman · Sun, 21 Sep 2008 11:19:54 -0700
Try replacing the strobe switch matrix strobe decoder on the I/O board (z15). If that chip is not working then the membrane switches will not be scanned properly.
Leo, thanks for the info but what is odd is I can reliably select the 50 presets. My thought is the membrane is okay. Something is wrong in the way the switches are interpreted when modifying the parameters. Does that make sense to you?
Leonardo Ascarrunz [no serial number] · Sun, 21 Sep 2008 16:48:50 -0600
I see. Is the the parameter mapping problem a display issue only or does changing the the actual parameter value affect the parameter it is "incorrectly" mapped to? For example, if you select P39 and slide the paramter control up and down while playing a note does the frequency cutoff change like it should or does the modulation depth change?
Dave Bradley [16330135] · Sun, 21 Sep 2008 21:58:44 -0500
Interesting quirk is: Switches that are a multiple of 4 toggle between the current value and previous value when the switch is repeatedly pushed.
Isn't this correct behavior?
Luca Sasdelli [21010226] · Mon, 22 Sep 2008 10:52:07 +0200
Hi Mike,
just a tip: disconnect all connectors on all boards, wash contacts on both sides with some contact fluid, dry them with compressed air (NOT with your own blow, because it contains water) and firmly reconnect them.
This just to avoid becoming a ghostbuster :-)
Michael Grossman [21030350] · Mon, 22 Sep 2008 07:35:58 -0700
On Sun, Sep 21, 2008 at 3:48 PM, Leonardo I Ascarrunz wrote:
I see. Is the the parameter mapping problem a display issue only or does changing the the actual parameter value affect the parameter it is "incorrectly" mapped to? For example, if you select P39 and slide the paramter control up and down while playing a note does the frequency cutoff change like it should or does the modulation depth change?
Leo, it does change the incorrectly mapped parameters. If I select P38 it affects the filter cutoff. I am going to check the eproms today at work to see if any are faulty.
Thanks for your help,
Mike
Michael Grossman [21030350] · Tue, 23 Sep 2008 00:49:55 -0700
My Chroma is working! It turns out the parameter mapping problem was due to using the wrong CMOS RAM part type. When I replaced the CPU and RAM, I substituted the 4334P-3 in place of the 6514-9 since it was called out on the parts list and the surplus electronics store had them in stock. After I repaired the corroded 2716 socket pin and the Chroma sort of worked, it did not occur to me that I had possibly introduced a new problem by using a different CMOS RAM part type. I originally suspected one of the EPROMs was faulty but after I verified them and then went on the replace the EPROM sockets that had been damaged by the battery acid, the mapping problem was still there. In desperation I switched back to the original 6514-9 CMOS RAM and miraculously parameter editing started to work as it should. I just spent a couple of hours playing the Chroma and marvelling at its capabilities. It is certainly a fantastic synthesizer. I still need to clean the keyboard contacts but for now I am absolutely thrilled.
Thanks to all,
Mike
Jesper Ödemark [21010135] · Tue, 23 Sep 2008 13:55:32 +0200
Congratulations!
It's always nice to hear people sharing stories like this one.
Leonardo Ascarrunz [no serial number] · Tue, 23 Sep 2008 15:04:08 -0600
Great! I would recommend replacing the power supply before you close the synth up for good.
Luca Sasdelli [21010226] · Wed, 24 Sep 2008 20:58:03 +0200
I agree with Jesper: really good to read such great repairs!
Michael Grossman [21030350] · Sat, 27 Sep 2008 11:22:49 -0700
I just wanted to update the debug log. After repairing the power supply, CPU and driver ICs my Chroma basically worked however 3 of the voice cards were defective. In order to troubleshoot the problems I setup the scratch patch, pressed split 31 to ignore bad channels and probed each of the 16 oscillator test points. Two were dead. It was fairly obvious the XR4151 chips were bad. After searching around and not finding the original part I discovered the NTE890. It appears to be an exact cross. A local TV repair store with a big selection of NTE parts had two left (lucky me). Replaced the chips with sockets and plugged in the NTE parts and lo and behold the oscillators starting working. One board started to pass the auto tune routine. Tracing further on the other I found the output of Z10 pin 7 was bad. I lifted all the resistors on its output to isolate it and confirmed the 4558 OP-AMP was bad. Replacing it got the second board working. The third board which did not have a dead XR4151 looked fine up to the VCF but the A-VCF output on pin 1 of Z14 looked like a high-pass filtered square wave. I started to pray that it wasn't the CEM3350. Thinking it might be the switch I replaced Z12 but no cigar. Replacing C13 did the trick. All boards are now passing auto tune. Wow am I happy. So now I want to finalize my precious Chroma. Any suggestions? The oscillators track pretty well but as I play the keyboard in 2 osc per note mode the beat frequency of some notes is noticeable. Is this fairly typical? Is it a bad idea to clean the contacts of all the voice boards or leave well enough alone? The last thing I want to do is open up a can of worms fixing things that ain't broke.
Thanks again to all,
Mike
Mark Smith [2103-PT-002] · Sat, 27 Sep 2008 12:03:57 -0700
Hi All -
It's normal to get up to 2 beats per second at an octave above middle C and double for the octave above that, worst case. The VCOs do need to warm up a bit so try an Autotune five or ten minutes after turn on.
Go to next message in thread, October 2008
Chemical Contact Enhancer
Mark Smith [2103-PT-002] · Mon, 22 Sep 2008 17:14:36 -0700
Hi all -
I've discovered an enhancer for electrical contacts. You paint it on - chips don't have to be removed from sockets. It's good for just about any kind of connection. Contacts need to be relatively clean before application. I've personally seen great results from this stuff. It's $50 for an OZ but will last for years - you use a drop at a time.
If you want to know more, check out this web page - http://www.stabilant.com/techt02h.htm
I'm not taking any responsibilty for negative consequences from using this stuff - you should experiment at your own risk. (I do not know of any negatives, I just wanted to protect myself.) I will accept thanks, though, for the tip!