CEM 3 Backplane

StradivariusBone

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So we suffered a lightning hit that seems to have nailed our DMX line between the booth and the rack. As a result it shotgunned nearly everything on the DMX run. Part of that was our retrofitted Sensor Classic rack. The CEM3 was throwing a config error, but failed at restoring the bad config on the backplane. Having a lot of experience diving into the classic racks, I was surprised to learn the backplane did much of anything, let alone store a config.

Anyway, after some back and forth it became evident that the backplane was in fact a victim and spared the CEM itself from further damage. Installing a replacement fixed all of our problems and we have since abandoned the under-slab DMX run as it is the second time we have suffered a lightning hit and it definitively confirmed for us that it is a favorite spot for lightning to go.

No real question, but I wanted to share because I thought it was pretty interesting that there's so much going on in the backplane now. There's a flash memory chip right next to the DMX line that suffered the hit. The other chips appear to be some kinds of microprocessors, I'm guessing for handling the ethernet port and maybe even the DMX ports too? One symptom was the CEM would not take any DMX input, but we were able to talk over sACN via the front port.

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It's not quite possible to read the part numbers in your picture (at least for me to make them out), but I suspect they are smallish microcontrollers, which these days can be surprisingly powerful. Communicating DMX512 is easy-peasy for pretty much any microcontroller larger than the very tiniest ones, though there's no inherent reason why it would have to be on the backplane vs. the processor card or elsewhere.

It doesn't look to me like there's the transcievers, etc. associated with ethernet, so I suspect that's not on the backplane. I could be all wrong. If I had to guess, the main jobs of the controller(s) there are such things as synchronizing/controlling power up and down, perhaps emergency override capabilities, storing configuration information (obviously from your problems), and other fairly basic systems management tasks. To some extent, this makes a lot of sense: you'd presumably want the emergency override controls to work properly even if the CEM is on the lam for some reason.
 
I can get a better shot of it tomorrow. We're gonna hang it on the wall. I'm not sure what all it does, but like I said it was interesting to see the development of that rack from the OG sensor to now. And especially considering the direction power distribution is going in theater, a rack of dimmers might as well be a dinosaur in some circles.

I am curious if there are two NIC's. When we were using the port on the front the Network light on the CEM panel did not light up, but it did when we switched to the one on the backplane. The storage of config in the rack proper seems to make a lot of sense for the touring crowd. Us install guys don't mess around with them that much, but it's nice to know it's there.
 
This is as good a time as any, I suppose, for me to promote my two favorite ham radio articles, both indexed under "heroic quantities of ferrite":

Oh, that's why I never post the links; one's a PDF.

The first article on this page, and the W1HIS piece further down:

http://www.ifwtech.co.uk/g3sek/in-prac/

Decent chance that a properly chosen ferrite core at each end of your long DMX and Ethernet runs will save you some hassle in lightning-prone areas, I suspect.
 
This is as good a time as any, I suppose, for me to promote my two favorite ham radio articles, both indexed under "heroic quantities of ferrite":

Oh, that's why I never post the links; one's a PDF.

The first article on this page, and the W1HIS piece further down:

http://www.ifwtech.co.uk/g3sek/in-prac/

Decent chance that a properly chosen ferrite core at each end of your long DMX and Ethernet runs will save you some hassle in lightning-prone areas, I suspect.
@Jay Ashworth "both indexed under "heroic quantities of ferrite":"
Quantities or qualities?
Toodleoo!
Ron Hebbard
 
So the CEM3 Backplane stores the config so we can rapidly swap them in an event of a failure. Moving a CEM between racks, will recognize that there is indeed a change in the rack config.

There is a spare DMX chip on the CEM3 mainboard that you can try swapping with whichever port isn't working.

The network port on the CEM3 is actually switched and is frequently used as a programming port by ASP's.
 

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