Lights turn on at shutdown

Question

Our house just got an Ion to replace the Obsession we've had for twenty years. 
 When we power off the console, sometimes lights will come up on stage. The lights that come on have nothing to do with the last cue that was run. Going to Cue 0 doesn't seem to help. 
 The racks are Sensors that were installed with the Obsession. 
 Any ideas?

pawpawtheatreman · Accepted Answer

I am working in a theatre that has very very old ETC dimmers and they just installed an ION. We get a lamp "ghosting" about every other time we shutdown. As was mentioned, ours usually turn off after lack of DMX signal for a few mins. I have found a quick fix that seems to work is to build a sub with a mix of channels in it, bring it up just before you are ready to shutdown, bring it down, shutdown and that usually clears the DMX.

derekleffew · Answer

nfarwell said:
... the Sensors hold the last seen DMX for 5 minutes.

How long the Sensors hold the scene is user programmable from 0-infinity seconds. See the appropriate manual under "Data Loss Behavior."

derekleffew · Answer

Here's the other thread where this was discussed at length: Shutdown glitch.

pwiegand · Answer

I go back to what David North states in another thread. DMX continuously streams information down the cable. On power down all consoles stop this stream. When the data stream is disrupted mid stream it can sometimes cause dirty data which in turn will drive DMX levels up. Think of it like blocking a stream with a log. There is going to be a splash. Where that splash happens depends on when you shut down the desk. Things to try: Bring down the grand master, enable black out, or manually select all the channels to 0. This way if there is a splash there is a good chance it is a value of 0.

MPenisten · Answer

It seems like the data you're sending at shutdown has no influence on this glitch. My experiences of this were mostly with an Express console and slightly questionable wiring practices. The order of operations was always to set all channels to zero, and then power-off. It was pretty common for a light or two to then pop on. 
 The only way I see to completely prevent problems would be to stop sending data cleanly at the end of a DMX frame, and then remove power from the DMX transciever (ideally doing that first, then powering off the rest of the console, but it might not be that critical). That way any garbled data generated while the chip is turning off should not be interpreted as a valid DMX frame by the receiving device. 
 edit: I should probably refresh the thread when I get interrupted for long periods between reading and posting... Basically; do what David says, he's usually right.

brucek · Answer

Kind of related, but I was wondering... 
 on say a CEM or CEM+... 
 If I send it an empty DMX frame (just a break-delay-break with no channel info), will the missing channel data be held (as loss of DMX)? or taken as 0%? 
 What triggers Loss-of-DMX? Is it no wiggle on the line? No break on the line? No data on the line? I know this is going to be specific to dimmer type. 
 Maybe if the dimmer could interpret the last look to hold as a few packets before the last valid packet (causing it to dump the last few corrupted packets)? 
 Anyway, my assumption has always been that no DMX data stream should be interpreted as all levels at 0%. The hold last look is purely for just-in-case. I would never turn on a work light or something using hold-last-look. I never use hold-last-look-forever. If the board goes down in a show, the worst case is going to be 1-2hrs. You never want to hold for ever without intervention (unless maybe you are an investor in electric utilities) 
 So then in the console at shutdown, DMX should put all levels at 00, and then disables the driver (right before? or right after? the break) I would think that there must be an available driver chip that has fail safe protection for its data lines