CMU200 repair attempt - shipping damage (oh those post monkeys...)

[Yansi]

Hello,

I have finally decided to get a CMU200, at least as an upgrade for my oooold spectrum analyzer.  So I have found a good deal, unit seemingly in a very good shape... only to find a month later, post monkeys played football with it.

Long story short: Unit was dropped hard on a corner (near the power switch), does not even power on. Chassis is deformed on the left side.

After further inspection and disassembly, I have found a sheared PCB in the computer module. And lot of other stuff one doesn't want to see: electrolytic cap(s?) that spilled their guts,  overheated BGA chips and fans seized so hard you can barely spin them by hand - even though there seems to be little to no dust inside the unit.

See photos below of the damage. Main PCB of the computer module has sheared  near the mounting point, inner layer traces more than likely severed. I do not think this would be an easy to repair if possible at all.

The question now is, can one get anywhere just the PC module to replace? I have searched ebay for these, found none for sale. Not sure if my search buzzwords were weak, or they are simply not available. I have tried even searching the part number printed on it, which I think is 1090.9244.24.

Can anyone point me please to where I could probably get a replacement PC for it? (Hoping the only electrical damage so far is just the PC).

Many thanks,
Yansi

[Qw3rtzuiop]

The CPU board is called FMR. They are used in several instruments built in "Bauweise 2000" (Translation: Architecture 2000).
They are several generations of these boards FMR5, FMR6.... . But i dont know if they are flashed for a specific model and if you can use a board of an FSV spectrum analyzer in an CMU200 even if it would be the same FMR generation.

[Yansi]

Yup, I have already found out it is called as such, in my case the board is "FMR6+T5" respectively. Thanks for confirming. They are probably interchangeable, as the whole FW sits on an externally connected HDD. But there maybe other firmware (such as the BIOS) specialized for the instrument. I have found that at least the FMR boards of different versions can be swapped for the same instrument.

Unfortunately, I can't find any board on sale. Searching  ebay I have found only two boards from Israel, both of which are some pretty old types with the price of way more than I have payed for the whole CMU. What a bummer!

//Hoping some will show up on ebay, or that someone will offer a spare one, if he happens to have one.  Is anyone willing to offer one, if you happen to have a spare?

I would prefer replacing it, rather trying to repair it. The shear line on the PCB goes under the connector on the other side, so almost impossible to repair the traces (not even trying to count internal signal layers, as the PCB is more than likely 6+ layer, would guess even 8 layer.) Repair attempt would need to start with X-raying the PCB first (which I could manage to do) to get an idea of the internal damage and how many traces has been severed.

[Qw3rtzuiop]

Based on my experiments the serial number (and therefore the instrument type and sub type) is stored somewhere on the FMR.
I wish you good luck on your search for an affordable replacement FMR. But that will certainly take a lot of time.
Until then you can try to repair your damaged FMR.
Is the orange standby led illuminated? Maybe your keyboard foil is broken too.

[richnormand]

Just looking at your photos for input so I might be totally wrong.

1)
On my CMU200 the small fan was  seized. I was able to remove it and disassemble the unit. After a bit of motor oil it has been humming for the past 4 years.

2)
Electrolytic cap. If you do not want to remove the pcb it can be gutted and replaced from the top with flying wires (Kluge warning,,, but it works).

3)
Overheating sticker. Mine had that too. Still working well.

4)
The crack on the pcb might be repairable assuming there are no internal fine traces in the inside layers. I have seen worse and only had to bridge the top trace.
Might be worth a close inspection after removing the unit under a binocular and a bright light before getting a replacement.

look at the battery while in there. Mine was dead.
Also, a shock like that might have dislodged a connector to the pcb. Might be a good idea to nudge all of them.

Best of luck with it.

[Yansi]

The unit was working before it was handed over to the post monkeys. Even though it had seized fan, blown cap and overheated BGA chip. But the PCB crack finally done it.

The PCB seems to have two signal layers on outer sides (I can clearly see traces on the first inner layer).

If you look at the photo, but zoomed in, you can see the inner layer traces too (sorry, photo not the best, can make a better one). There is at least a dozen of them broken on the layers I can see, not sure if there are any internal signal layer in between the outer most power planes.

[TheMG]

Long story short: Unit was dropped hard on a corner (near the power switch), does not even power on. Chassis is deformed on the left side.

Thus the importance of proper packaging, something that unfortunately too many eBay sellers fail to do properly.

How was the unit packaged? Large heavy items like this really should have at minimum 15cm of foam on all sides, and a double-wall box or nested boxes. All too often I see people use newspaper or bubble wrap, neither of which are any good for heavier items as it compresses too easily. Packing peanuts are also no good as the peanuts move around and the item ends up sinking to the bottom of the box while in transit.

Tip: before and during unpacking, always take pictures, so if you find the packaging was inadequate resulting in the item getting damaged, you will have evidence to file a claim for a refund.

[Yansi]

Packaging was definitely inadequate.  I got refunded half the price I have payed for it: the unit cost was  about $500 (just the basic model without any interesting options), so if not counting the shipping and VAT, I got a $250 boat anchor now (shipping and VAT excluded).

This refund problem is already solved, but the boat anchor needs a new PC board to become a CMU200 back again. 

[TheMG]

I would attempt a repair, maybe you'll get lucky and repairing any visible traces (including the ones on lower layers that you can see through the board) will make it work again. At this point, you've got nothing to lose. Worst case is you've put time and effort into it and it still doesn't work.

Looks like most of the traces lead to vias, so visually follow the traces to a via or solder pad, and use those as points to solder mod wire to.

[Yansi]

I could attempt repairing it, but I think that the damage it got is way in the BER region. The crack is much longer (after inspecting closely - see photo) and I can count 20+ severed traces in there.  The crack is right under the connector, so not much access to the other side of board to at least see where the traces go.   

//EDIT: Inspected more closely: There is 8+2 traces on the component sides broken and likely 5 on the other. But I still need the Xray to determine the connections of like half the traces. 

If the Xray attempt will be successful, I think that bodging 15 traces shouldn't be as that bad, they seem to be only quite short links. I'll try to get an Xray of the board now.

[ogden]

Close to humanly impossible repair unless you have schematic *and* gerbers. I would start to look for spare board or buyer of this unit as it is (for parts or repair).

[Yansi]

Of course no schematic and no gerbers, the only think I can try is to get the Xray image of the board. If not, then to trash with it. 

After seeing the availability of replacement boards (little to none), it would make sense to sell it as trash for parts. But I would rather wait selling it, until I get another unit - I may need other replacement part for it too.

Also, I have asked two persons specifically, that could have the replacement computer, we'll see if I succeed there. 

[ogden]

Of course no schematic and no gerbers, the only think I can try is to get the Xray image of the board.

That looks like 6 layer board to me, traces could be shadowing one another all over the board. Single image won't help, rather 1 or more hours of "live" 3D X-ray tracing. There's catch - even one trace buried under BGA and you have problem bodge-wiring it.

In case of few inner-layer breaks one could try using dremel to carefully dig in, but in your 20 traces case it seems like hopeless 0.1% success rate idea.

[Yansi]

Bad news everyone,

the röntgen maschine brekken ist.  So I am not able to let my friends do an Xray of the board on a proper electronics inspection machine.  Fuuu***ck.

So the only option is to get a replacement board. Anyone willing to sell one? 

[richnormand]

possible interest?
FMR5 and front for CMU200 for sale:
https://www.eevblog.com/forum/buysellwanted/fs-(eu)-cmu200-front-panel/

[Yansi]

By no means I am an expert CMU200 rebuilder, can somebody explain, if an older computer (FMR5) can be fitted into a machine where FMR6 was originally?  And when/how I can obtain the firmware that will work both with the old board and the newer rest of the instrument?

From what I have learnt so far, there should be some kind of a "version manager" that will rebuild firmware from scratch for the HW detected, but it requires to have a suitable image to put on a fresh HDD drive (or CF card, if one wants). Where to obtain a workable image of the drive is still a mystery to me. Although this thread also reveals a lot of interesting info about the CMU: https://www.eevblog.com/forum/testgear/enabling-options-for-rs-test-equipment/50/

[Qw3rtzuiop]

I dont think the initial firmware is needed. The offered FMR was already initialized and is taken from a CMU200. Im just not sure if you will get a new serial number. And after change you should start the "firmware update after board change" to be sure. You dont need a fresh installation for that.

The service manual contains a hint that there seems to be different connectors of the FMR. But the model 04 is the unit with the FMR4 board an model 12 with FMR5. I would assume that the later versions share the same connector. But you can check that. The service manual wasnt updated after they changed to FMR6 (or i dint have the lastet version avaiable).

BTW. The price offered is pretty good if you consider that there is also the keyboard and the lcd included. The keyboard is another main source of failures.

[Yansi]

Connectors may be compatible, sure, but the PC software is not, is it? I have already a likely working HDD drive with the original FW for FMR6, but I would likely need a different firmware for FMR5.  Or will FMR5 run from the FMR6 HDD drive? That's what I am asking. If someone can confirm, I will buy the FMR5 right away.

[Qw3rtzuiop]

The main difference between the FMR versions are the CPUs. But it is just a PC with some IO. I dont see any reason why it shouldnt work. Upgrades from FMR5 to FMR6 are prooven to work. But you can ask the seller if he can give you an image of his hdd.

[Yansi]

Just thinking about the compatibility - you sure FMR5 can be plugged into a FMR6 backplane? Just noticed CMUs with FMR5 computer boards have only 5pin DIN keyboard connections, while the FMR6 equipped CMUs have USB ports on the back (although I have learned they are only emulated USB ports for KB/Mouse and nothing else). But I think there is no electronics on the backplane, so the USBs must be interfaced directly to the FMR - hence thinking, there may be an compatibility issue between FMR5 and 6? Am I right or.. ?

[Qw3rtzuiop]

The CMU200 I used to have was equipped with an FMR6 and a motherboard with PS2 connector on the backside. The serial number on the back was different to the one that was displayed in the menu. It worked but had some input level issues caused by a broken DIG board.

[richnormand]

Another FMR5 board:
https://www.ebay.ca/itm/184462065687?ul_noapp=true

[Yansi]

That board is unfortunately an economical nonsense. I can buy almost a whole unit for that kind of price.      (one needs to add all the import fees and VAT to that to see where I see the issue, as a poor european)

And yup, I have bought another unit for parts. Got extremely lucky to buy it very cheap. Or maybe I can repair this one if not the first one? Seller stated that "it does not turn on". So I pretty much hope it is a PSU issue, as SMPS is what I can deal with, should I repair one.

All repair attempts currently on hold, waiting for all the parts and stuff or people getting out of quarantine.

[Yansi]

Little update on where we are at:

I have received another boat anchor from Israel: Yet another non functioning CMU200. This time it is the most basic configuration, likely with FMR5 or older computer, almost without any additional SW options. Just some GSM stuff - at least according to the stickers I see through the cover on the side.

I do not have the unit at home yet, need to move it another 40 km to my lab. The described issue is "does not turn on". Well, I have tried to bravely plugg it to mains, it turned on instantly upon flipping the switch at the back. But the display remained black. Once I pressed the front soft power button, it instantly turned off and I couldn't turn it on any more. (I did not try any further).

Does this problem looks like any of the typical ones with these units?

I bought this unit very cheaply, almost for scrap price (shipping was more expensive than the unit itself). Wanted it especially for two things: It may have a functional computer and also importantly it has the 50W rated input module! I hope I can salvage it as a downgrade for my unit (as the 50W is the base configuration and my more recent unit has the 2W input option).

Is there any argument why the 2W option is better, than the 50W? Is the 2W option better in anything? I could not find out.

It would be nice to have both units repaired in the end. But I still don't have any other spare PC yet. But one spare FMR5 will be on the way shortly, including the whole front assembly with LCD any keyboard.

Still need to negotiate the FMR6 (supports USB ports) for my main unit.

Also meanwhile I have received another upgrade module for my main unit, the B17 (Analog IQ/IF interface).

So, thats where I am at now.

[Bicurico]

Let me give you my advice:

Sell your boat ancors on eBay for the best price possible and get yourself a fully working and stuffed CMU200.

Otherwise you will end up like me: I know own a total of 3xCRTU and 2xCMU200!

It started when I bought two broken CRTU in hope of building one working unit from it. I ended up buying some missing components (some from Israel) and managed to get BOTH working.

Then I stumbled on a great deal for two broken CMU200. So I bought another broken CRTU to get the required parts to make both CMU200 working. The last CRTU is actually working, too, but without any option at all.

Looking back, I might have spent the same money as 1-2 working units are currently sold on eBay.

Was it worth it? For fun yes, but perhaps it would have been better to just get one fully loaded CMU200 (option wise) in fully immaculate state. None of my 5 devices pass the self-test 100%. And that is the sad reality of these devices: if the RX/TX self tests fail, you will in most cases not be able to correct the out of spec parameters.

Is this a big issue? Not really - except you need immaculate measurments at exactly the failing frequency range.

Another option is to get the Siglent SSA3021Plus...

Regards,
Vitor