Power Sequencer not sequencing.

[josh88]

Here's the scenario. I went away for a day and my rack won't turn on anymore. I can open the rack up (which was locked in the back so should have been free of prying hands) and bypass the sequencer and everything still works fine so it seems to be narrowed down to the sequencer or switch. Everything was fine on tuesday but not this morning and I can't think of anything that would have changed. Does any of this make sense? I'm planning on calling the folks who installed it, but figured I'd check here first incase theres something obvious that I"m missing. Any ideas?

Front of rack with Power led lit up

back of rack, everything seems to be exactly the same.

 

[MNicolai]

What you have there looks like a USC-6R. It's a 6-step sequencing controller that outputs signals to each of the RLM relay modules in your vertical power raceway in your rack. Each of your RLM modules are standalone relays that switch on or off as the USC-6R tells them to.

If some of the modules are sequencing, then the fault is probably a short or disconnected wire between the outputs of the USC-6R and the inputs of your RLM modules.

If none of the modules are sequencing, then the fault is likely with your USC-6R.

What happens when you hit the Power Up or Power Down switches? Do the status lights sequence up or down, or are they non-responsive?

If you want to identify if the controller is working but the switch mechanism is bad, you can short the terminals on the back of the unit with a paperclip. On the REMOTE connector, shorting between COMMON and UP will sequence the system on. Shorting between COMMON and DOWN will sequence the system off. If the system sequences correctly off of the REMOTE terminals, then the problem is likely a faulty switch on the front of the unit.

 

[josh88]

The paperclip is exactly what I needed. None of the modules were coming on and shorting them fixed it. Now I know! thanks for the tip.

Next question. with the connection for the remote switch removed it powers up and down perfectly. BUT if I reconnect the remote connection in the back it cycles the system off. Should I read that the connector in the back may be shorted somehow and telling it to turn off?

 

[MNicolai]

When you say "shorting them fixed it", do you mean you shorted each of the modules individually or that you shorted the UP/COMMON DOWN/COMMON on the back of the USC-6R and it properly sequenced all of the modules up and down?

If shorting the REMOTE connection on the back of unit worked, then you should give your installer a call and tell them that you're pretty sure the Power Up / Power Down switch mechanism on you USC-6R needs to be replaced.

 

[josh88]

When you say "shorting them fixed it", do you mean you shorted each of the modules individually or that you shorted the UP/COMMON DOWN/COMMON on the back of the USC-6R and it properly sequenced all of the modules up and down?

If shorting the REMOTE connection on the back of unit worked, then you should give your installer a call and tell them that you're pretty sure the Power Up / Power Down switch mechanism on you USC-6R needs to be replaced.

I shorted the UP/COMMON and DOWN/COMMON on the back and it cycled on and off fine. I realized though I didn't need the paper clip because once the connection in the back was removed so that I'd be able to short the terminals on the back, the switch in the front started working again.

The remote connection on the back has been there since it was installed so why would it suddenly start preventing the front switch from working, because its fine once I break those connections.

 

[MNicolai]

Could be that whatever your REMOTE terminal is connected to has a short at the other end. That could be a wall switch somewhere, which could be stuck in the POWER ON or POWER OFF position. If the USC was detecting that on the REMOTE port, it could have been overriding or otherwise preventing the front panel switch from working.

 

[josh88]

I will add that the other end for the remote switch isn't connected yet, that end is still sticking out of a conduit because the work hasn't been finished. Could that end be causing the problem? it hasn't been an issue for a month but maybe that end got jostled and the wires are connected and doing the same as shorting the DOWN/COMMON?

 

[josh88]

I just checked the other end, separated the two wires and taped one of them to be sure they weren't touching but when I plug the connecter back in, it goes back to being unresponsive.

 

[josh88]

Ok, working through this, I just took the wire attached to the DOWN portion of the connector and moved it to the UP portion and reinserted the connector. It immediately cycled everything on. But now its the reverse, the switch won't turn it off. Remove the connector in back and the switch functions normally again. I do actually have the switch for the other end so I'm going to temporarily hook it up and see what happens

 

[MNicolai]

Could be that the wire got nicked on the edge of a conduit during installation and the conductors are shorted together or shorted to the conduit.

My inclination is to say that if it's the installer's responsibility to put the switch in, leave the REMOTE cable disconnected and let them worry about it when they finish installing the remote switch.

 

[josh88]

I think thats what we'll end up doing, attaching the other end didn't seem to make any difference. Just frustrating when nothing seems to have changed since yesterday. A nicked wire that shifted somewhere is about the only thing I can come up with to explain. Thanks for the help Mike. Definitely steered me in the right direction.