Smartpacks not seeing DMX

[jayvee]

Hi folks,
I am helping out a friend whose got some misbehaving lighting. The setup is an Element > 125' run of DMX cable > wall jack > conduit to a rack of six (6) daisy chained Smartpacks. Pack 4 of 6 is the only one recognizing DMX signal from the console or my Nomad. Packs 1,2,3,5,6 have blinky DMX lights. To the knowledge of the drama teacher, the packs have never been serviced since install and they are full of dust and crud so I'd agree. I'll be bringing a shop vac on my next visit.

So far I've:

• Deep cleared the console and restored a 1:1 patch to all 72 dimmers.
• Tested the 125' DMX run from the console to the wall jack - tested fine with two separate testers and does control the number 4 pack via console and Nomad.
• Tested wall jack to rack panel jack - tested fine with two testers, controls number 4 pack via Nomad.
• Test ran each pack to full and out via Diagnostics on the pack - all connected fixtures ran to full and out.
• Verified all settings in each pack for normal operation.
• Connected Nomad to each pack individually - no packs EXCEPT number 4 recognize DMX signal from Nomad. All DMX lights continue to blink except number 4, which remains solid.

Currently they are unable to locate a breaker or switch to de-energize the rack so I've stuck to all the testing I can do without going into the rack. The staff at the school are getting a maintenance/electrician out to address that issue tomorrow.

I'm attaching some pics of the front of the packs and the back of the rack. One pic shows a wire that looks like it came loose and is dangling - that is the number 4 pack, the only one that IS working.

I'm not sure what to try next. I'm eager to reach in and reattach that one errant wire but won't be going near it until they can shut the power off to the rack. I'm reaching out now because I feel like I'm missing something and look to y'all, who are smarter than I, to help me out. I did consider DMX chip failure but it seems unlikely that 5 out of 6 would fail at the same time though who can say with covid disuse and lack of upkeep.

What am I missing/should I look for next?

Thanks for any help you can provide!

 

[Mac Hosehead]

From what you have described, I would say you could indeed have some failure on each pack with the DMX input. I would not consider multiple failures to be unusual if something harmful happened to the input line.

 

[cbrandt]

That sounds like a classic case of bad DMX chips to me. The fact that 1 out of 6 is still working is probably luck. Something bad went down those lines and fried the chips.

It is a bit concerning that no one knows how to locate the disconnect to shut down the racks though.

 

[jayvee]

The drama teacher said there was some construction over the shutdown. Would a power surge to the racks cause chip failure? If so, how should the racks be protected in the future? What else should I check for damage? Replacing the chips doesn't look super complicated - do they have to be done by ETC?

And yes, I expressed concern over the disconnect situation. They are eager to address that as well.

 

[FMEng]

Try a reboot of the rack, first. A power surge could damage the dimmers, but I would suspect lightning more. DMX receiver chips seem to be vulnerable, especially since a long run of cable is a great antenna for lightning energy. I wouldn't be surprised if that particular chip is socketed for easy replacement.

 

[jayvee]

Try a reboot of the rack, first. A power surge could damage the dimmers, but I would suspect lightning more. DMX receiver chips seem to be vulnerable, especially since a long run of cable is a great antenna for lightning energy. I wouldn't be surprised if that particular chip is socketed for easy replacement.

Will try deep clear of each pack tomorrow.

 

[jayvee]

Try a reboot of the rack, first. A power surge could damage the dimmers, but I would suspect lightning more. DMX receiver chips seem to be vulnerable, especially since a long run of cable is a great antenna for lightning energy. I wouldn't be surprised if that particular chip is socketed for easy replacement.

Lightning! Intriguing. How can I protect them in the future?

 

[FMEng]

Lightning! Intriguing. How can I protect them in the future?

You could try prayer. I wouldn't worry about it. Every strike is different, and the odds of it happening again are very small.

 

[Malabaristo]

Are these actually grounded properly? I noticed a distinct lack of green wire in those pictures, but can't see the power input terminals... Also, it's pretty odd that they chose to install those bus bars for the neutral wires when there's a convenient (and preferred) place to land them right on the back of the packs. Is that neutral bus isolated from the (presumably grounded) body of the equipment rack? Connecting neutral to ground anywhere but the service entrance is generally frowned upon by code. Improper grounding can make everything more susceptible to damage from messy power or lightning, so getting that sorted out with a competent electrician would be a good place to start.

If this was installed correctly, you're not looking for one disconnect, but six. Each pack should have its own 2 or 3-pole circuit breaker that could be rated at up to 60A (for 2-pole) or 40A (for 3-pole). The big problem with SmartPacks in my opinion is that they don't require an ETC tech to be involved in the installation, so they miss out on that quality check. While I'm sure it happens sometimes, I've never actually seen a site where the installation was 100% correct and code-compliant.

The DMX chips are socketed and are the standard 75LBC182 (pin compatible with a 75176). I want to say there's even a spare mounted on the board, but it's been a long time since I've seen the inside of a SmartPack. The hardest part about swapping is disconnecting everything to pull them out of the rack and get the top covers off.

 

[derekleffew]

A quick check that might prove illuminating.
Only Pack#4 works? Address them ALL to Pack#4. What happens?

 

[jayvee]

Are these actually grounded properly? I noticed a distinct lack of green wire in those pictures, but can't see the power input terminals... Also, it's pretty odd that they chose to install those bus bars for the neutral wires when there's a convenient (and preferred) place to land them right on the back of the packs. Is that neutral bus isolated from the (presumably grounded) body of the equipment rack? Connecting neutral to ground anywhere but the service entrance is generally frowned upon by code. Improper grounding can make everything more susceptible to damage from messy power or lightning, so getting that sorted out with a competent electrician would be a good place to start.

I will get better pics of the entire rack back situation tomorrow and double check. I can't believe I didn't get a full pic.

If this was installed correctly, you're not looking for one disconnect, but six. Each pack should have its own 2 or 3-pole circuit breaker that could be rated at up to 60A (for 2-pole) or 40A (for 3-pole). The big problem with SmartPacks in my opinion is that they don't require an ETC tech to be involved in the installation, so they miss out on that quality check. While I'm sure it happens sometimes, I've never actually seen a site where the installation was 100% correct and code-compliant.

Intriguing. Will check tomorrow. This makes sense since my own Smartpacks each have a 3 pole breaker.

The DMX chips are socketed and are the standard 75LBC182 (pin compatible with a 75176). I want to say there's even a spare mounted on the board, but it's been a long time since I've seen the inside of a SmartPack. The hardest part about swapping is disconnecting everything to pull them out of the rack and get the top covers off.

They've ordered the chips so we'll know soon.

 

[RonHebbard]

I will get better pics of the entire rack back situation tomorrow and double check. I can't believe I didn't get a full pic.

Intriguing. Will check tomorrow. This makes sense since my own Smartpacks each have a 3 pole breaker.

They've ordered the chips so we'll know soon.

I'd be interested in measuring for voltage between the rack and a known good ground followed by neutral and a known good ground.
Toodleoo!
Ron Hebbard

 

[Amiers]

Very crazy that pack 4 in the middle of the chain is the only one that works.

Also finding the disconnect won’t do you much good when the smart pack has an on off switch on it already.

Does sound like the chips.

 

[almorton]

Not that I'd expect it to cause such mayhem, but I don't see a terminator - is there one plugged in or does the last unit have internal termination? I'm not familiar with these units so don't know if that's possible; I know some Zero88 dimmers have automatic termination if there is nothing connected to the DMX out, for example.

 

[jayvee]

While it's true that they each have their own off switch I am not putting my arms in the rack until I know that power is off to the whole situation.

 

[jayvee]

I did consider that and am bringing one over today.

 

[Amiers]

While it's true that they each have their own off switch I am not putting my arms in the rack until I know that power is off to the whole situation.

Oh god no, merely stating you could power cycle them and clear whatever nonsense they might be holding and redress them and see if it works. Which is likely not gonna work.

 

[jayvee]

Oh god no, merely stating you could power cycle them and clear whatever nonsense they might be holding and redress them and see if it works. Which is likely not gonna work.

Yeah, that didn't work. Though one did come up in Spanish, which was exciting.

 

[Malabaristo]

Also finding the disconnect won’t do you much good when the smart pack has an on off switch on it already.

THIS IS NOT TRUE!

Sorry, for yelling, but this is an unfortunately common and potentially dangerous misunderstanding: the first breaker in a SmartPack is not a main breaker. It only cuts power to the control electronics and has no effect on the rest of the power flowing through the pack. If, for example, you have a bad power cube where the output is stuck on, turning off this breaker will have no effect on that circuit. Even if it were a main breaker on the pack, you would still need to cut power upstream of the pack in order to pull it out of the rack.

You absolutely need to locate the breaker(s) feeding these packs before attempting to do any work on them. (Which I realize jayvee already understands, but I don't want to leave this out there for other readers.)

Not that I'd expect it to cause such mayhem, but I don't see a terminator - is there one plugged in or does the last unit have internal termination? I'm not familiar with these units so don't know if that's possible; I know some Zero88 dimmers have automatic termination if there is nothing connected to the DMX out, for example.

SmartPacks are self-terminating (unless they're really early models), so you probably don't need to add a terminator. Definitely true if made in the last decade+. No harm in trying, though.

 

[FMEng]

SmartPacks are self-terminating (unless they're really early models), so you probably don't need to add a terminator. Definitely true if made in the last decade+. No harm in trying, though.

The self termination relies on a switch in the panel connector. Switch contacts don't stay happy unless they get operated regularly, and that one isn't. It would be worth plugging in a terminator to see if it helps.