ChromaTalk Archives: August 2004
- Chroma For Sale
- Galaxy Users? (2 messsages)
- Picture of Syntech Retrofit?
- Chroma power supply failed (4)
- Fwd: Rhodes Chroma For Sale
- ARP Digital Access Control (23)
- Chroma Repaired
- Source for L60V6 (5)
Chroma For Sale
Chris Ryan [21030691] · Sun, 1 Aug 2004 14:18:37 -0700
From Analogue Heaven (Doug, how could you?!):
Date: Sun, 1 Aug 2004 04:34:03 -0700 (PDT)
To: 'Analogue Heaven'
From: Doug Terrebonne
Subject: FS: Synths & Studio GearHi, selling the following:
$800 Rhodes Chroma (SF Bay Area only)
[...]
This is Chroma 21030401.
Galaxy Users?
Chris Ryan [21030691] · Fri, 13 Aug 2004 12:05:31 -0700
Does anyone on the list still use Galaxy for Chroma patch storage and retrieval?
David Gowin [21030611] · Fri, 13 Aug 2004 15:19:33 -0400
Not I
David's was the only response I received; for now, Galaxy format patches are still available on the Patch Downloads page but I may not keep them around forever.
Picture of Syntech Retrofit?
Chris Ryan [21030691] · Tue, 17 Aug 2004 21:31:20 -0700
Anyone have (or can take) a decent picture of the Syntech/Chroma Cult/KMX midi retrofit, with the Syntech markings?
Thanks to Jack Colburne and Chris Now for the pictures they sent (see the main Syntech page).
Chroma power supply failed
Jimmy Moyer[21030184] · Wed, 18 Aug 2004 03:51:28 EDT
Today's sure to go down as an infamous day in history. After nearly 22 years as my master keyboard, I powered up my Chroma to a blank display. Starting at the obvious place, I find my digital +5 supply is only around +0.6. All the other supply voltages are close to spec.
So a couple of questions come to mind before I start to study the, um interesting looking regulator design.
What's the common wisdom these days? Try to fix it or replace the whole supply? Any late news on custom reset circuit boards? Any regulator debugging tips? Possible or probable the supply took stuff further downstream along with it?
Using the Chroma as a master keyboard in 2004 is probably a little like using the 1933 Packard as a commuter car. But, I'm pretty much fatally accustomed to the feel. Last I looked, the feel of current keyboards fell into two camps, too heavy piano emulations and too light 'synth actions.' Anything that feels like a Chroma?
Thanks,
-Jimmy-
David Clarke [21030085++] · Wed, 18 Aug 2004 19:38:27 -0400
What's the common wisdom these days? Try to fix it or replace the whole supply?
From the list traffic I've seen, it seems about 50/50 in terms of 'fix' or 'replace' - but I don't think that many of the 'replace' votes were specifically because the supply _couldn't_ be fixed; rather, most of the folks who've gone that route didn't want to keep the original PSU any longer.
As you've been happy with the original PSU for 22 years, I'd vote for the 'fix' option (and I'd double my vote if you're happy poking around with electronics - as there's so little in the PSU that can really go wrong).
Any regulator debugging tips?
There's only a handful of components in there, so I'd first recommend checking the easy things - such as confirming that the two main diodes feeding the digital side are OK, and then reading the voltages across the couple zener's in there (to see that you are seeing the expected drop across them).
If you haven't done so already, it would be recommended to disconnect the P2 and P3 PSU connectors (to confirm that it's not a failed component elsewhere in the system pulling the 5V rail down).
Possible or probable the supply took stuff further downstream along with it?
Unless you have a specific reason to suspect it (scorch marks, etc.), I would say "no."
Using the Chroma as a master keyboard in 2004 is probably a little like using the 1933 Packard as a commuter car....
I'm a great believer in the idea of 'whatever you're most comfortable with is the best thing to use...'
Jimmy Moyer[21030184] · Thu, 19 Aug 2004 16:02:09 EDT
Well, poking around is free, so I'll start with that.
(My background is on the software side of things, though some hardware, mostly digital, not analog, rubbed off many years ago, so any help is appreciated. Thanks.) Dug out the scope and the DMM...
I only have roughly 1V across C3. On the DC side of the rectifiers I have what looks right to me - double hump, 28VP, though with a positive spike about half way up the positive going side - not the sort of bite out the service manual mentions. Points to trouble in the pre-regulator, no? I've got reasonable readings across the zeners.
At Q3 C I have 4/12V pulse 20% duty cycle, 120 Hz. All these signals are 120 Hz from the rectifier.
At Q2 (couldn't find pinouts but assume 1=gate, 2=source, 3=drain) S 0/6V 20% pulse, S same as output from rectifiers, Drain is a 2/4V ramp 20%. This doesn't look right to me. Could be pulled down by Q1? (which is too hot to touch)
So I'm suspicious of Q1 and Q2. I'd replace them both. Sound right?
Jimmy Moyer[21030184] · Thu, 19 Aug 2004 17:51:19 EDT
(Just ignore that last message.)
One other thing I noticed was the over voltage protector screwed to the top of C3 was warm. Thought that shouldn't be so, with only about a volt across it. Pulled it off and -- voila! Normal boot up. Yeah!
I seem to recall people running without this. Dangerous? The archives show some discussion of availability but no solution and a search for L60V6 just shows those couple of parts brokers.
While it's apart, I've had a couple of ERR boards for a while now, time to check them out...
Fwd: Rhodes Chroma For Sale
Chris Ryan [21030691] · Thu, 19 Aug 2004 08:21:11 -0700
They have another restoration in progress.
Begin forwarded message:
From: "Music Control Information" <info@musiccontrol.co.uk>
We now have one fully restored Chroma available. The serial number is: 2101017s [I assumed this should be 21010175]
The instrument has had a full cabinet restoration too & is working perfectly.
Chris Ringham [21010021] performed some modifications & upgrades to the power supply. It has Rev 14 Software & a piggy back board for the ADC.
This instrument could come with the Syntec MIDI interface (Chroma cult) if required.
We are looking for 1500 UKP for the instrument.
Let me know if you need any further details.
Many thanks & kind regards
Chris Simpson - Vintage Synthesizer Sales Manager
Tel: +44(0)1270-883779 Fax: +44(0)1270-883847
ARP Digital Access Control
Chris Ryan [21030691] · Sun, 22 Aug 2004 19:25:51 -0700
In Michael Salmon's [21030155] short review of the Chroma at the Vintage Synth Explorer site, he writes, "Rhodes used ARP's proprietary Digital Access Control which was used in some ARP instruments for inter-connecting them. Midi retro-fits can be purchased these days which convert MIDI to ARP's DAC system."
Is this true? Were there ARP instruments that used, if not the Chroma's 25-pin "Triad" hardware connector, then at least some software-compatible version of it?
Jack Colburne [21030142+] · Mon, 23 Aug 2004 00:23:38 -0400
I remember the term "Digital Access Control" as referring to the single digital slider/control usually-one-parameter-at-a-time programming style of the Chroma, DX7, Poly-61 etc.
Roland's digital bus was the DCB, "Digital Control Bus" (JP-8, Juno-60). There were/are several boxes to connect MIDI gear to DCB. But Vintage Synth's JP-8 and Juno 60 pages seem to mention the DCB correctly.
Maybe there's some confusion between Triad and a reference to the programming style.
Most definitely could be wrong, but I didn't think ARP used any digital bus on any other gear.
David Gowin [21030611] · Mon, 23 Aug 2004 10:01:50 -0400
Definitely nothing on the ARP side for HW or SW digital interface, they used CV, Gate and Trigger interface only. None of the ARP synths had any computer intelligence (even though supposedly the Quadra had a computer built in, but that was more for patch mngt)
The first majorly public references I saw to the ARP/Fender/Chroma TRIAD interface was in the pre-release brochure for the Polaris, son of Chroma.
Here's a portion of the brochure linked above, showing the Triad logo:
Erik Vellinga [21010286] · Mon, 23 Aug 2004 22:14:08 +0200
Hi Chris,
I would like to correct the following about the Fender Triad Interface;
The parallel port as it is on the Rhodes Chroma is called Chroma Interface with its own set of instructions, different but comparable to MIDI protocol. The Triad Interface is a serial port just like the MIDI port only at a double (62,5Kbaud) rate!! The source of this info, the Polaris service manual, mentions that the Triad Interface protocol is under development at Fender and works like MIDI only the data is send in packages and uses a different timing routine.
I have included a copy of this source in the attachement. Sorry about the size but I could even hardly read the original as it is.
Here are cropped versions of the images:
If the above scans are a bit difficult to read, the first highlights the text "two independent, symmetrical parallel ports" under the the heading "Chroma Interface;" there is another heading indicated that says "MIDI/Triad Interface." The second scan points out the text "The Triad Interface works like the MIDI interface, except it runs at 62.5Kbaud instead of 31.25Kbaud ...". The third scan is from a schematic which clearly shows separate MIDI, Triad, and Chroma (25-pin) interfaces.
I wonder if the Polaris has a Triad connector on its back?
Chris Ryan [21030691] · Mon, 23 Aug 2004 19:54:45 -0700
This is very interesting information--so the Polyphony article is incorrect (it says that Triad "lets users connect instruments to computers via a 25-pin D-connector cable").
I wonder if the Polaris has a Triad connector on its back?
Can any Polaris owners verify this?
Jeffrey D. McEachin [21030073+] · Mon, 23 Aug 2004 20:39:01 -0700
There's not one on my Polaris.
David Gowin [21030611] · Tue, 24 Aug 2004 09:30:02 -0400
Yes it does, I'm starting to play with getting my Polaris to talk with my Chroma via the Chroma/Triad interface. What I'm hoping to try to see if it works is, can I slave my Chroma to my Polaris via the Chroma interface, then use the MIDI interface for recording and playback of both?
Chris Ryan [21030691] · Tue, 24 Aug 2004 09:07:40 -0700
If the Chroma interface is 25-pin and Triad is serial (I assume a 5-pin DIN connector?), how do they connect? Did you get an adapter with your Polaris?
David Gowin [21030611] · Tue, 24 Aug 2004 12:31:49 -0400
Nope, it's a 25 pin connector on the Polaris as well. The 25 pin connector is just that, depends on how it's wired that determines serial, parallel or even SCSI (but who am I to say to you! You're prob way more up on this stuff than I)
If anything, I hooked up my Chroma to my Polaris with the Chroma 25 pin cable, they do communicate.
Chris Ryan [21030691] · Tue, 24 Aug 2004 11:54:28 -0700
On 24-Aug-04, at 9:31 AM, David Gowin wrote:
Nope, it's a 25 pin connector on the Polaris as well. The 25 pin connector is just that, depends on how it's wired that determines serial, parallel or even SCSI (but who am I to say to you! You're prob way more up on this stuff than I)
Not necessarily; I'm a musician and programmer but hardware? Forget it. :)
If anything, I hooked up my Chroma to my Polaris with the Chroma 25 pin cable, they do communicate.
Is the 25-pin connector labelled "Triad"? I was just at the local music store this morning; they have a Polaris (I) for sale and it only has MIDI and "Chroma Interface" on the back. Maybe the Triad interface was on the Polaris II?
Doesn't look like it: see back panel photos posted by Doug Terrebonne in May 2003.
David Gowin [21030611] · Tue, 24 Aug 2004 15:17:34 -0400
I have a Polaris 1 (although there really wasn't a production run of the next version of the Polaris, the Expander was supposed to come first which also never happened).
I'll have a look, I think it said Chroma Interface but will check to make sure.
Chris Ryan [21030691] · Tue, 24 Aug 2004 13:37:44 -0700
On 24-Aug-04, at 12:17 PM, David Gowin wrote:
I'll have a look, I think it said Chroma Interface but will check to make sure.
On 24-Aug-04, at 6:30 AM, David Gowin wrote:
I'm starting to play with getting my Polaris to talk with my Chroma via the Chroma/Triad interface.
I think we're back to the beginning on this. This sounds like my original misunderstanding. Just to be clear, Erik wrote:
The parallel port as it is on the Rhodes Chroma is called Chroma Interface with its own set of instructions, different but comparable to MIDI protocol. The Triad Interface is a serial port just like the MIDI port only at a double (62,5Kbaud) rate!!
The schematic he sent [see above] shows THREE distinct interfaces: MIDI, Triad, and Chroma. (Although I am no expert at reading schematics, it looks to me like the only 25-pin connector. I could be wrong.) So there is no "Chroma/Triad" interface port. They are different. Or would have been, if the Triad interface had been implemented on the Polaris.
On 24-Aug-04, at 6:30 AM, David Gowin wrote:
What I'm hoping to try to see if it works is, can I slave my Chroma to my Polaris via the Chroma interface, then use the MIDI interface for recording and playback of both?
There was a discussion about using the Polaris as a Chroma-to-MIDI in February.
See thread Polaris as Chroma-to-MIDI?
The 2004 archives will be online with the new site.
Doug Terrebonne [21030114] · Tue, 24 Aug 2004 15:50:05 -0700
--- David Gowin wrote:
I have a Polaris 1 (although there really wasn't a production run of the next version of the Polaris, the Expander was supposed to come first which also never happened).
I have a Polaris II and it is rare but i've seen a few others over the years so there was definately a production run...
The II also only has MIDI and Chroma jacks...
David Clarke [21030085++] · Tue, 24 Aug 2004 19:14:21 -0400
Triad System
The scan [see above] that was attached is very interesting, as it does not appear to be the exact information in the standard Service Manual (at least not the original that I have, dated 1985).
What's even more interesting is that portions of the information is in the service manual that I have.
Specifically, the section in that document is only called "MIDI Interface", and the last para. of the section reads "...Counter Z84 and sections Z82, Z85, and Z47 are not used in the Polaris. The purpose of these circuits is to support a proprietary interface protocol under development at Fender." The section stops there whereas the scan goes on for another handful of sentences talking specifical about the Triad interface.
The schematic portion appears to be the same (or at least very similar) to the Midi Interface portion of the standard service manual.
Based on the info in the scan, it appears that the Triad interface is really just clock doubled MIDI (from the hardware point of view), with the other differences being handled in software. If I interpret the data provided, you would have either had access to the Triad system OR MIDI - but not both at the same time (i.e., they'd use the same physical connection).
If I had to make my own version of history I'd guess that Fender used the term "Triad" loosely. I'd bet that the first incarnation of so-called Triad interface was indeed the "computer interface" found on the Chroma (the DB-25 on the Chroma and Polaris). The "Triad" name would make sense, since if you did use the Apple II, you could connect up a Chroma, Expander and the Apple interface (3-chroma interfaces) into one system, etc. Given that the Polyphony article pre-dates the Polaris somewhat, this seems reasonable.
Perhaps because of the advent of Midi (and the fact that an 'expander' never really did just become a way to 'add on more channels' to the Chroma), Fender may have deciced to re-invent Triad as a proposed DIN format on the Polaris ...
I've never seen any reference to anyone ever having run in the clock-doubled mode (on the Polaris I or II) but I've never taken the time to disassemble the '186 Polaris firmware - but it wouldn't be a stretch that this feature could be in there (esp. since most of the other characteristics about time-tagging of events, etc. appears to already be supported internally on the Polaris).
Jack Colburne [21030142+] · Wed, 25 Aug 2004 02:14:25 -0400
Re: Triad System
David Clarke wrote:
If I had to make my own version of history I'd guess that Fender used the term "Triad" loosely. I'd bet that the first incarnation of so-called Triad interface was indeed the "computer interface" found on the Chroma (the DB-25 on the Chroma and Polaris)...
I agree with David. I had always thought that Fender was originally referring to the 25 pin parallel port on the Chroma. The Polyphony article seems to support this idea. I had, mistakenly, thought that they finally decided to make it "official" in the Polaris advertising.
It makes sense that the 25 pin connector on the Polaris is not the Triad connector. Chris had a good point: if the Polaris' DB-25 was a serial interface, it shouldn't talk to the Chroma's parallel interface. They would not be speaking the same "language" no matter what the pinouts on the connectors were. The Triad would be passing a single piece of information at a time over a single pin, the Chroma would be expecting 8 simultaneously. If David C. is right about utilizing the MIDI connectors, the Triad connector was unidirectional. The Chroma parallel interface is 16 data pin bi-directional; 8 data pins in, 8 data pins out on a single cable. Triad would need 2 DIN cables like MIDI.
But all this still leaves Chris' original question. What is Michael Salmon talking about when he refers to the ARP Digital Access Control? My Guess: I not so sure the term was supposed to refer to the computer interface. I still think that if he saw the term in print somewhere, it may have been refering to the programming style. Even today "DAC" refers to using e.g. a touchpad, to enter values to gain access to a locked device, etc.
"The Source is one few mono synths to employ digital access control in place of knobs and switches and one of not many more to offer program memories." quoted at Analog Synth Gallery Moog Source page.
"DIGITAL ACCESS CONTROL provides precise push button control over every program parameter for creating and editing programs." from the Korg Poly-800 manual. (caps are Korg's)
...there are other references to the Korg Poly61, Korg Wavestation, etc. They all use the same terminology. There's no mention, to my knowledge, of the term Digital Access Control in any of the Chroma literature.
But then again, maybe DAC was ARP's early name for the computer interface. Has anyone seen this term in some obscure literature/article referencing an ARP product?
And then again, maybe Michael Salmon is simply mistaken. His email address on the Vintage Synth site no longer works... couldn't ask him.
A puzzle.... thanks a lot Chris. (grin)
David Gowin [21030611] · Wed, 25 Aug 2004 14:14:01 -0400
I think we're back to the beginning on this. This sounds like my original misunderstanding. Just to be clear, Erik wrote: [...]
My mistake then, sorry about that.
David Clarke [21030085++] · Wed, 25 Aug 2004 22:10:03 -0400
But all this still leaves Chris' original question. What is Michael Salmon talking about when he refers to the ARP Digital Access Control? My Guess: I not so sure the term was supposed to refer to the computer interface. I still think that if he saw the term in print somewhere, it may have been refering to the programming style. ...
I have to agree. When I saw the subject line of the first e-mail in this trail, my first thought was of the slider + button entry method.
Reading the actual Vintage Synths writeup at that time I thought that Michael Salmon must have just made a typo ...
But then again, maybe DAC was ARP's early name for the computer interface. Has anyone seen this term in some obscure literature/article referencing an ARP product?
I haven't seen any. I've never seen any references like this.
The closest other item that I can think of is what ARP sometimes labelled as "System Interfacing" (such as on the Omni, Axxe, etc.) - but that was really just CV/Gate on 1/8" jacks.
The 1-page ad for the Chroma's closest ARP brother (the Quadra) says "...Additional synthesizers can be interfaced with the Quadra through ARP systems interface jacks..."
Chris Ryan [21030691] · Sun, 29 Aug 2004 14:37:38 -0700
One more tidbit about Triad. I just noticed gathering some information on the Polaris for the new site that a magazine ad [actually the first product brochure] featuring the Polaris prototype says:
"Polaris is the first of our Chroma-based synthesizers to come with our new Triad computer interface. It lets Polaris store computer information internally and communicate that data to a host computer in non-real time. With Triad and your own personal computer you'll perform (and store) extremely long, complex, multi-instrument compositions. Manipulate stored data and 'mix' tracks. Change sequences. And do an incredible variety of musical tasks. Plus, Triad makes it easy to interface your Polaris to any Chroma instrument, today or in the future."
Here's a reduced version of the ad. Click for the full-size original.
The first? Maybe a mistake. I wonder if this ad was ever actually published. Tony Williams did mention that the instrument was vaporware for a long while.
Jack Colburne [21030142+] · Mon, 30 Aug 2004 21:51:26 -0400
1) from David Clarke:
"...Additional synthesizers can be interfaced with the Quadra through ARP systems interface jacks..."
Yeah... I remember the Quadra as having a mess of CV and/or CV/gate jacks. It had some processing on board, but I think it was just for patch memory of a sort.
2) From Chris Ryan:
a magazine ad featuring the Polaris prototype
Even for a preliminary ad, that description of the Triad interface is pretty vague. The ad copy makes the Triad interface sound like... well... MIDI. Or like... well... the Chroma interface. Doesn't really say much. It can store "computer information internally and communicate that data to a host computer in non-real time"... meaning that it can probably dump its internal sequences as well as patch data. Still pretty vague.
The ad in question goes on to say that.... "... the Triad interface makes it easy to interface your Polaris to any Chroma instrument, now or in the future." So, it sounds like this ad must have meant the Triad interface to be the 25 pin D-connector.
So, we're sort of right back where we started...
If the specs Chris forwarded are correct, and not just a version of the tech manual that was never actually "real", then this whole Triad thing sounds as if a bunch of people at Fender couldn't make up their minds what the heck it was supposed to refer to.
David Clarke:
Fender may have decided to re-invent Triad as a proposed DIN format on the Polaris ...
Makes sense; and it seems that the release of the Polaris must have come right in the middle of the "re-invention". Makes me wonder if the 25-pin Polaris "Triad" was supposed to be simply a new more consumer-mainstream software package (big brother Chroma compatible) driving the same hardware.
Chris, is there a version date on the full size Polaris Service Manual scans sent to you? I'm curious if it is later or earlier than the "standard" manual David C. refers to.
David Clarke [21030085++] · Mon, 30 Aug 2004 22:30:12 -0400
As this thread still seems to have some legs, I'll toss in a few other notes.
While the service manual that I have doesn't have the same body as the scans that Chris forwarded, a closer read of the 1985 service manual does specifically mention Triad.
The "Strobe Decoders, Miscellaneous I/O" section refers to the "MIDI/Triad interface." As it read it, it seems to be talking about them as a combo implementation.
Further, the MIDI interface writeup of the same manual does talk about the ability to select 31.25K or 62.5K as the baud rate - as set under SW control.
The Polaris' MIDI document [see Polaris: Manuals] outlines a SYSEX implementation that would allow the user to gain access to the guts inside the Polaris, including all of the sequencer data, etc.
If I were a betting man, I'd say that the fancy Triad statements made at the time of the Polaris were are reference to a clock doubled MIDI interface, using the same connectors for send and receive as MIDI would, with 'meta data' being passed over the interface per the SYSEX defintion. A lot could have been done with that interface - but there would have had to have been a good computer app to allow the parsing and management of the SYSEX data to actually make it useful (and I've never heard of anything like that ever seeing the light of day...)
Chris Ryan [21030691] · Tue, 31 Aug 2004 00:25:50 -0700
Chris, is there a version date on the full size Polaris Service Manual scans sent to you? I'm curious if it is later or earlier than the "standard" manual David C. refers to.
Not on the scans Erik originally sent--Erik, do you have a date?
David Gowin [21030611] · Tue, 31 Aug 2004 09:31:31 -0400
I can check on the date in the next day orso. The service manual was sent to me from a gentleman (can't remember his name now) who was a contact at Fender and was supportive of the Polaris User Group I was trying to run. He was also very kind in sending not only a full memory upgrade kit for my polaris but a new and faster CPU that what was normally shiping with the Polaris at the time.
Let me check on the date...
Chris Ryan [21030691] · Tue, 31 Aug 2004 10:08:28 -0700
There's no date on the scans that Erik originally sent--the ones that show the Triad, MIDI, and Chroma interfaces.
Recently I received new scans of the Polaris Service Manual [14mb] from Ben Kuris of the Polaris mailing list. They have a date of 1985. Incidentally, the port labeled "Triad" on Erik's scan corresponds to MIDI Out on the 1985 version--see the attached graphic.
Chroma Repaired
Werner Schöenenberger [21010114] · Mon, 30 Aug 2004 19:45:05 +0200
Hi List,
I just joined this list because I recently succeeded in the repair of a Rhodes Chroma. Based on the information found on the web site of Chris Ryan I was able to fix the unit and I am happy about his great site. Only few people put their effort into a documentation like he does - Thanks a lot.
Uh - it took me about 3.5 years to solve the four problems and many times due to the backstrokes within the investigations I put away the work for a couple of weeks or months. Well at least, the synthesizer now works again and I was able for the first time to hear the instrument. Originally I intended to sell the Chroma but now I am not sure and am thinking about to add a MIDI retrofit to the instrument.
See Werner's post Broken Chroma and replies, September 2000.
Well for anybody being interested in the story of this particular Chroma, here it is. Perhaps it might help anyone to fix his Chroma with less effort:
I think that I needed more than 80 working hours to fix the unit - most of the time to figure out the problems. And what is described below in some few lines of text took me hours and hours.
There were two main problems: The Chroma did not boot anymore and all voices did not tune at all.
a) no booting
First I checked all the power supply and the processor clock. Everything seemed to be ok. After a long time, I found that I could reset the Chroma manually by pulling up the reset pin of the processor. Further investigations showed that the reset circuit for the start up phase had a small delay. The delay was based on the two capacitors in the reset circuit that came to their age. They still worked but did not load in the specified time anymore. This leaded to a slight flatter slope and a delay of the RESET signal that did not reset the microprocessor in time. I exchanged the capacitors (C10, C12 in the schematics) and the CHROMA booted correctly. So if a Chroma does not boot correctly, the reset circuit is a good area to search for the source of the problem
b) all voices did not tune at all
First I checked the D/A circuit and the timer circuit. Everything seemed to be ok. Later I found that the problem was in the I/O Strobe Decoder circuit that drives the different boards. I had to replace Z41 (74SL138). One single latch had a burn through. Exactly the right one to avoid tunig. Now 7 of 8 boards could be tuned.
c) tune of board #5
It took me a couple of hours to figure out that board #5 as well as the Channel Mother Board had a defect. First I had to figure out the Channel Mother Board. Here I found that one single latch in the flip flop Z9B (4456) had a burn out. After replacing it, any board tuned at any place in the system. The final problem in the Dual Channel Board based in the defect of TWO 4151 (Z2 & Z3). I was definitely surprised that both of the two ICs died at the same time and so first, I searched in the wrong direction. But finally everything worked, I even did not have to re-calibrate the voice boards. You cannot imagine how lucky I was ;-)
Best regards from Switzerland
Werner
Source for L60V6
Jimmy Moyer[21030184] · Tue, 31 Aug 2004 19:28:27 EDT
I found one of those parts brokers who would sell me a reasonable quantity (10) of the L60V6 over-voltage protector used in the Chroma power supply. Though it works without one, it seems like reasonable insurance to have.
It doesn't seem as if these (or any replacement) are any longer manufactured. I put one back in my Chroma and am planning to add one or two to my cache of emergency parts.
I'd be happy to sell the rest at my cost ($16/each) plus shipping. Just email me.
Arti Haroutunian [21030388] · Tue, 31 Aug 2004 19:00:16 -0600
Another option for the overvoltage protector is the NTE part which crosses to L60V6:
NTE4906 Zener Overvoltage Transient Suppressor, Unidirectonal Ipp = -124A, Vbr = 7.79V Min, 8.20V Max.
This comes in the same package as a 1 Watt Zener, not a TO-3. $1.38 at the local parts store. I think that this part was mentioned in a discussion here a few years ago.
See Z4/Overvoltage Protector (Lambda L60V6) Availability (December 2003).
David Clarke [21030085++] · Tue, 31 Aug 2004 22:11:45 -0400
I'd be happy to sell the rest at my cost ($16/each) plus shipping. Just email me.
Jimmy - while I don't currently need one of these myself, I do appreciate the effort of you going through the ordering process with the parts broker on behalf of the list/group.
Thanks!
David Clarke [21030085++] · Tue, 31 Aug 2004 22:14:04 -0400
Arti wrote:
Another option for the overvoltage protector is the NTE part which crosses to L60V6: ...
Arti - I took a quick look via the on-line NTE cross reference and I didn't see the L60V6. Can you tell us how you located the cross?
On a related note - does anyone have a spec. sheet for the original Lambda part? (outlining specific electrical characteristics, etc)?
Arti Haroutunian [21030388] · Tue, 31 Aug 2004 21:01:06 -0600
I took the part # to my store and he looked it up on his DOS NTE cross reference. Maybe it's an older part that they no longer manufacture.
I haven't seen the original data sheet.