scary dmx fixture failures

[drphoto]

This past weekend we had a important show. About 30 minutes before start of first set one of the lights (a venue thinpar, which is a7 ch rgb wash light, and comprise most of my system) started behaving erratically. I start checking dmx addressing, then channel settings, replacing dmx cables, then suddenly everything downstream of this lights just goes haywire. Everything is flashing randomly and I have no control what so ever. It turns out that quite by accident I find one fixture that has a bad dmx output socket (broken solder joint) I'm pretty new to DMX lighting in general but it seems pretty scary that with using a serial connection, if one unit fails it effects everything down the line. Seems like a bad design concept.

Have any of you had this issue? how do you deal with it? Gear will fail, especially these fairly cheap DJ fixtues. Do you carry spares for everything? Can lights be disabled in software?

I finally got everything working with about a minute to spare. I had to position the bad light 'just so' as to keep the connection. It was hard to run the show after that as I was so stressed.nono

BTW: no software issues, V7 and midpipe seems to play nice and all is well on that front.

[support]

We are not pro on gigs, but our answer is:
- yes all fixtures are on same dmx line, in serial
- if one fixture corrupts the dmx line, then all light will not work anymore
- it is not possible to fix that from the software, because the dmx line is out of service

[Lighter007]

Maybe 5 Pin DMX Connections can help..? I actually don't know what 4th and 5th Pin are for..

But I've never have heard of this problem before. In such a situation I would think its because of a broken cable..

[marco]

An other solution is to disconnect the bad fixture and connect the 2 cables!
Better then position the "bad fixture"

[Earl Harvey]

Yep... Place the fixture at the end of the DMX chain...
The 4th and 5th pin are for DMX channels 513 - 1040... FYI

[Pink LD]

Yes. 5 pin DMX connectors were originally intended for 2 universe support. I can't recall I have ever seen it used that way in the last 13 years I have paid attention to lighting control.

As to troubleshooting faulty fixtures? In the old days of dimmer racks and moving fixtures the failure was easy to identify. When your chain failed? It was obvious it was good up to the fixture that was working and the problem lie from the output of the working fixture to the input of the non-working fixture. However, nowadays I find many fixtures that fail can often send erroneous data both ways, i.e through the send and return lines of DMX. Accordingly the whole daisy chain of fixtures go haywire.
First of all I use an opto-isolator to distribute DMX data to various daisy chains. And then when a daisy chain goes haywire, I halve the problem. I go to the half way point of daisy chain and disconnect. If rig is still haywire? then it is earlier in the daisy chain. If that cures the problem, then the problem is later in the daisy chain. I keep on halving the chain whichever way I need to go until I find the faulty fixture/cable.

One a troubleshooting note: I carry XLR Y's both Male Male Female and Female Female Male. You can bypass a faulty input or output fixture connector by putting an XLR Y on the known good in/out DMX port and then connect the daisy chain through the Y. I do it in show situations all the time to get through a show with having to bypass a fixture and then I can get to repairing the fixture post-show and at my leisure.

[LightWorx]

Pick up a isolated DMX splitter and split you show on to different channels. A isolated splitter works by accepting DMX input, it duplicates and amplifies the signal to all of its output channels. Since all 512 DMX channels are broadcast on each of it's outputs you can plug your fixtures or chain of fixtures into to any output you want. Your fixture addressing is not affected. I was able to pick up a 8 way isolated splitter on EBAY for about $100.00 is has been working flawless for over three years. With a isolated splitter if a fixture or cable goes bad only the devices on a particular channel get affected and it is much easier to troubleshoot problems. Plus the isolation prevents any shorts or stray voltage getting on a DMX cable from going back and damaging your USB to DMX converter. I run about 40 fixtures in my show and split it 6 ways. Down stage lights, Up stage lights, Stage Right lights, Stage Left lights, Effects, and Movers. Remember as with any DMX chain, you need to place a terminator resistor on your last device. So if you split into six channels as I have you need to terminate the last device on each channel.