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-   -   JL Cooper MSB+ REv. II troubleshooting/fixing. (

raito 28th December 2015 04:27 AM

JL Cooper MSB+ REv. II troubleshooting/fixing.
(pictures to come)

So last week I decided to really, truly, this time rewire my rack gear (again). So I pulled all the gear out, made sure all the cables were labeled, put it all back, including a couple new (to me) patch bays (the reason for the rewiring), and nothing happened. This rack is nearly all MIDI stuff, so nothing happening meant that no MIDI was going anywhere (audio is just fine).

Checking over my (so I thought) trusty (OK, secondhand) JL Cooper MSB+ REv. II, I noticed that I couldn't get it to change modes. Also, button #1 didn't appear to work (2-8 did). Now, that #1 button has always had a bit of trouble, as in you had to press on the lower part of it to get it to register sometimes, and the mode button sometimes acted like it wasn't debounced. But none of that should have kept it from sending or received MIDI data.

So let's open it up and see what we can see.

First off, the case is a touch odd. One piece of metal comprises the entire case except the faceplate. Off come the 4 screws, but the face remains on. A little messing with it reveals that it's still held by a pair of connectors. OK, I can pull it off. It's a pretty simple 2 sided board, with most of the traces towards the faceplate, which is still held to it by 3 nuts. The pushbottons are pretty simple SPST types with only the 2 solder points. There looks to be a few odd diodes in there, but no logic or anything else. I'll meter this later to see if the switches are working OK. The connectors are 15-pin.

The main board is held in the case by 5 standoffs. I'll have to remove the not and washer for the footswitch, too. It's apparent it's not the first time this unit has been opened. I can see a heat sink with a finger or two bent some, and there's some ceramic caps at the front of the board laying down flat against it. I doubt that they wre put in that way. I can also see that several of the chips are socketed. More than normal, even, So I pull the board.

On one side is a small power section. There's a 7805, and what is probably some associated circuitry. Seeing that the input is supposed to be 9VDC, I can see that this just brings the voltage down to what the chips need. The maibn processor is a Z-80, and there's a ROM socketed next to it (when I post photos I get the rev. info off it). Next is a series of larger socketed chips that I currently take to be RAM. There's a few various 7400-series logic chips, too, and some of them are socketed. There's Sharp 900 opto-isolators on each of the MIDI inputs, as you'd expect. And one large chip down at the other end of the board.

I can't see any reason why anyone would socket a garden-variety 7400 -series chip. And if it was manufactured that way, why not socket everything. That, and the somewhat crappy soldering job I see on some of the chips, convinces me that this has been opened before.

I check the seating of the socketed chips. I get the usual old slightly crunchy sounds you know by heart of you work on equipment like this. I'd bet even money that the thing will work now. And if it doesn't 2 to 1 that it's a bad solder joint on one of those chips.

There's also a battery. Well, it had been holding programs so it's probably good, right? I decide to check. It's a coin battery, and it's held in by a pair of metal pieces, one on top, the other on the bottom. OK, I'm not really familiar with this method, but it sure looks like I can remove the battery, right? Wrong. Those 2 metal bits have a couple of needle points sticking into the battery.

OK, I nearly always replace fixed batteries with removable, and I have a hold and batteries, so I just pry the metal bits off the battery. It's tests OK.

Since I'm getting a little tired tonight, this is as far as I'll take things. Mark which battery connector does to + and call it a night.

Tune in next time...

raito 29th December 2015 06:23 AM

1 Attachment(s)
1. 7805 +5V regulator. Its capacitors are to its upper left, its resistor right above it.

2. 7493N 'S' logo. 4-bit binary counter.
3. Xtal section. Xtal is marked 8.00 MHz

4. MC74HC00AN Motorola logo. quad 2-input NAND gate
5. Z80. Didn't write down the full number.

6. ROM. Most of it is covered by the paper JL Cooper lable. Verison is 2. something. 21V FAST peek out from under the label.

7. 98851 'ST' logo. STMicroelectronics 2K x 8 CMOS STATIC RAM

8. 2 8927 'ST' logo. Asynchronous Communications Interface Adapter (2 MHz).

9. MC74HC138AN Motorola logo. 3 to 8-line decoder/demultiplexer

10. 8461A0 Mitsubishi logo. quad 2-input OR gate

11. Array of transistors and resistors. Probably LED drivers.

12. 8424KO Mitsubishi logo. BCD to decimal decoder Note the 'LS' on this one, bipolar, not CMOS.

13. P8936G Double-lightning logo. octal register with three-state outputs

14. 7406 PC 'F' logo. hex inverter buffer/driver with 30 V open collector outputs
8419(?) Singapore

15. MC74HC244AN Motorola logo. octal buffer with noninverted three-state outputs

16. PS 900V Optoisolator. Required by MIDI electrical spec.

17. CD221003 I couldn't find this one. Might be CD22103? CMOS HDB3 (High Density Bipolar 3) Transcoder for 2.048/8.448Mb/s Transmission Applications
RCA H 823

18. M74HC151B1 'SCS' logo. 8-line to 1-line data selector/multiplexer

19. CD74HC22106E QMOS 8 x 8 x 1 Crosspoint Switch with Memory Control
RCA Z 906

20. Battery. After replacement.

Most of it makes perfect sense to me, except that CD221003 (or 03).

Pretty clever circuit. I wondered how they moved data from 8 MIDI ins to 8 MIDI outs with a processor of the time. Turns out they probably use that CD74HC22106E to just make it a bunch of THRU ports. Very cool.

raito 31st December 2015 05:58 PM

Well, the front panel is now working. Holds patches and all.

But still no MIDI. More testing necessary. It's entirely possible that it's a user error on my part.

It's also likely that there's a bad solder joint somewhere.

raito 16th January 2016 03:31 AM

Well, isn't this interesting.

Apparently, it was user error on my part. Unplugging the MIDI cable from the master keyboard and replugging it made everything work again. Of course, only after I tore down half the rack. Such fun! No one but myself to blame.

And this after acquiring another one. But this second one has a different power connector (standard barrel connector instead of a 2.5mm phone), and it looks like all the switches have been replaced. This one also came with an old parallel MOTU MIDI Express.

Looks like time for more gear!

Jidis 17th January 2016 10:35 PM

Thanks for all the info Raito! I'm saving it, as I've also got that box.

When I first started reading and saw that you were having problems, I was thinking stuff needed to be cleaned and reseated. Mine went in once and that was all that was wrong, and I think the second time it malfunctioned, I had the sense to go in it myself, and it was the connection to the display board or something.

I need to power it up again soon for some stuff. It's been sitting a long time, so I'm sort of expecting it not to act right, but at least I'm no longer afraid of it.

That's a weird company. To this day, I'm running into specialty stuff they made years ago that I've never seen in my life, and the market was nowhere near what it's like now. It would be interesting to know what sort of quantities some of it was produced in.

Take Care

PS- I always hated that tip/sleeve power plug - spark city if it gets pulled wworried

raito 19th January 2016 06:10 PM

I'm glad it helped someone.

I'll probably open up the newer one, maybe this weekend, and try to see what the differences are. I'm particularly interested in whether it has the same goofy battery connection and whether the same or different chips are socketed.

My guess as to my initial problem is that the display/button board connection got jostled when I pulled the unit out of the rack, probably because the front panel didn't quite slide out cleanly past the units mounted next to it. The second problem, as I say, was operator error.

And yeah, they're an odd little company.

I've already jumped a spark on that power connector a couple times. Fortunately, it didn't fry anything. wworried But I'm not sure I want to try and replace the connector, either.

raito 19th March 2017 05:06 PM

Pretty sad that it took me over a year to look inside my second MSB2. But I've recently expanded my rig, like a good GS member, and I needed the extra capacity.

The newer one actually has a revision number on the main board (Rev. 16). It's a lot cleaner layout. I think the newer barrel-type power connector is part of the revision as the rear panel has the polarity in the silkscreen. The resistors near the optoisolators are gone, replaces with resistor arrays. The optos themselves are now socketed.

I still think the pushbuttons on the front panel were replaced, and probably at least one of the LEDs. The soldering there looks a little different.

This one was probably just made a few years later than the first.

enage 20th July 2017 03:08 AM

I have a MSB, and several buttons stop working overnight.. like WRITE, 2 and 7..
Press them and nothind happends...
What can i doto fix it?

raito 1st August 2017 02:00 AM


Originally Posted by enage (Post 12747105)
I have a MSB, and several buttons stop working overnight.. like WRITE, 2 and 7..
Press them and nothind happends...
What can i doto fix it?

You might need to just take it apart and clean the contacts between the main and display board. I did find when putting it back together that part wa a bit sensitive.

raito 28th September 2017 04:17 AM

Since I wrote the initial breakdown, I've acquired 2 more of these. I took one apart tonight, and started working to reverse-engineer the schematic, for my own fun. This one is a lot cleaner on the inside, and is one of the later versions with the resistor arrays and barrel power connector.. The 2 chips marked #17 are 4X4 crosspoint switches, probably there to deal with the MIDI processors in some fashion.

One modification done to this unit is that the battery was removed, and 2 AAA batteries glued to the front panel with silicone caulk, then wires soldered appropriately. I think I'll be removing all that and putting in a standard CR2032 holder and battery.

RichTone 8th August 2019 05:50 AM

Hey all:

I’ve got a MSB V2 a friend dropped off that failed to power on out of no where.

I’ve reseated all the socketed ICs and probed the power jack. I get +5v on pin 3 of the 7503 and +10v on pin 1. No lights on the panel. Heat sync gets warm/hot. That’s as far as I’ve gotten without a schematic. Oh, I also checked all the switches on the front panel board with DMM and they all check out.


raito 1st October 2019 04:09 PM


Originally Posted by RichTone (Post 14137796)
Hey all:

I’ve got a MSB V2 a friend dropped off that failed to power on out of no where.

I’ve reseated all the socketed ICs and probed the power jack. I get +5v on pin 3 of the 7503 and +10v on pin 1. No lights on the panel. Heat sync gets warm/hot. That’s as far as I’ve gotten without a schematic. Oh, I also checked all the switches on the front panel board with DMM and they all check out.


All mine have 7805 regulators, not 7503. What are you getting out of the negative output pin?