A nightmare gig - what to do?

[smokeAndMirrors]

Hey mods, there's no general chit-chat forums here, maybe we could use one?

Anyhoo: I did a gig on Friday, and it was a qualified disaster. Get-in was late - 2:30 (show start at 9 mind), and I had submitted a plan to the band that basically made sure I had till 5:15 until they started setting up. They agreed to it. However they soon forgot that, and at 4:30, before I had sorted out the power, they asked if they could put their drum kit up. Big flippin' softie me said "ok". Next thing I know the guitarist has put his ring in the corner, taken 2 power sockets, the bassist is also doing the same, and the drummer has his drums and cymbals everywhere. I can hardly move for people or stuff. Then as soon as the guitarist sets up he starts his own sound-check and I can't hear myself think. Ditto the bassist and then the drummer. Then the support acts turn up and they start setting up and my access to the lights is blocked off at the back and sides and there's no power left.

6pm was switch-on. Nothing worked. I had a faulty power lead. Replaced it, a few bits worked but it was all still screwy. I tried new DMX cables. I double-checked the addresses. No avail. I got a few bits working but I could barely reach some of the fixtures, I panicked, and so by doors-open I had mostly given up with half the rig half working. The stuff that did work flickered really badly. The right-hand half didn't work at all, except for an occasional glitch. The show went poorly, but as well as could be expected given all that.

I only asked for half my fee. The band were really nice about it, kind of "stuff happens" (ironically their van packed in after the show and they ended up stuck there at 1am waiting for rescue). Back home, after a long lie-in and a day to mentally pull myself back together, I did an equipment test, and discovered that a faulty scanner had caused at least some if not all of the problems.

So here's a question. Is it possible to create some sort of debugger to help diagnose setup issues? It seems the faulty light affected not just fixtures *after* it (physically) in the chain, but in those *before* it. That suggests that Daslight might be able to do some kind of analysis? In the cold light of day, I realise I should have started disconnecting fixtures one-by-one, but are there any other tips out there to help that time when you switch on and nothing happens?

[simonB]

I've had the same problems so many times! Somehow I've always managed to get it all working at the last minute perhaps with just one faulty light. I did a gig for a 10 piece big band on a tiny stage once. No one bothered to tell me they were doing a rehersal from 4:00. I arrive at 2, 20 steps I have to walk up to load in so it's nearly 3:00 before I get to properly start setting up. The band arirve at 4 and cram the stage before I've even finished.Keyboard player unplugged half my rig to plug in his keyboard. Nightmare!

Anyway I would always recommend you use a DMX splitter. This way you can send the same DMX universe to 4 different areas for example. This means you can isolate the problem and save your self a potential 3/4 of debugging time. Unfortunatly with the DMX protocol being as rubbish as it is (no data integrity checks, can only send 512 8bit blocks at a time, only 1 way communication unless using RDM with the small amount of compatible devices etc...) there is no way to test the signal that I know of other than testing each cable. You should also consider purchasing a cable tester if you don't have one already. I had a 1meter cable which worked fine when using less than 8 fixtures, but when put near the end of a DMX chain it messed up half the rig. I borrowed a cable tester from the sound guy only to realise one of the connections was faulty in the center of the cable.

A couple of other advantages..
-A DMX repeater/splitter usually gives the signal a bit of a boost, so can help with issues near the end of the DMX chain.
-Each serial datastream has less distance to travel so less chance of corruption
-The outputs are electrically isolated. Once I used a fixture where some idiot had wired a new plug and had wired the live to the ground. I fired up the rig all at once me being the idiot that I am. 8 of my cheap chinese LED pars went pop and I had to replace the DMX board on each.
-If you are ever using anyone elses gear, sometimes they may be using 5pin instead of 3. Most repeaters/splitters come with both sockets.

Take a look at this..
http://www.thomann.de/gb/stairville_dmx_splitter_4.htm

It probably costs less than the money you lost that night!

[smokeAndMirrors]

Thanks simon, that looks eminently sensible. And (in a way) I'm glad to hear that I'm not the only one who has suffered at the hands of musicians in this fashion.

[Crafty1980]

It happens to EVERYONE!! I've had it twice in a row (even after a complete debug of my rig after each show AND before the next one!)... Needless to say, I was having sleepless nights on the third show in a row but it did all work!!

What I've done now is this:

I've set up a seperate Daslight file to allow quick semi-debug of fixtures and wires...

Basically, it's a basic test for each fixture that you can turn on and off in turn. I have 11 Martin Roboscan Pro 518s so before installing them on the rig, I line them all up on the floor from 1-11. They all have their own DMX cable which is colour coded with in and out of each fixture. (FYI Rather than tags, I use insulation tape of various colours and patterns. e.g. Yellow tape with thin strip of red tape in the middle of it etc, etc)

Then run Daslight.

The first scene I run is a test of all fixtures: 0%>100%>0%>50% Pan, 0%>100%>0%>50% Tilt, Colours, Gobos, Effects. If something is't working with any of the fixtures it soon flashes up something is wrong!

If, for example, no fixture is working past No.4, then first thing I do is take the fixture out altogether (i.e. Take out DMX in and out and stick them together!) If fixtures 1-3 & 5-11 are all working then there's a problem with fixture 4... If not, there's a problem with the dmx before or after that fixture... etc...

It took a while to set up, but not I can debug in about 10mins and, since having those problems, I've had to do it a couple of times and both times I've been commended by my professionalism of sorting out a problem!!

Forgot to mention that I've also got a second scene group setup to do the same thing to each fixture one after the other... That one is more to just look good when the rig is up and tested before performance! ;o)

[simonB]

haha sounds good. Yes DMX can be really temperomental sometimes, especially with the cheaper fixtures. The worse scenarios for me is when it's all working fine and then one of the mirrors of the scanners will tiwtch, or a shutter on a moving head will twitch, and even if I have everything set to off there is little that can be done other than running onto the stage and cutting the power!

[SEAMUS]

I Use dmx controlled relays on all movers then I can cut power to any fixture that shows a problem during a show.

[mnoethlighting]

Not sure if this has been said yet, but you should terminate your DMX runs (fancy speak for "use a cable with a 120-ohm, 1/2-watt resistor soldered between pins 2 and 3 on the connector at the end of the run"). 1/2-watt is the minimum. A 120-ohm, 1-watt resistor is best.

Here's why:

The data rate for DMX512 signals is 250,000 bits per second. This is fast enough to put a DMX512 signal into the category of signals knows as "radio frequency", or RF. RF signals behave strangely, if you are not used to the characteristics of these signals. For instance, if you have a piece of wire carrying an RF signal, and the end of the wire is just a cut end, then that cut end acts as a "mirror", and "bounces" the signal back down the wire. Radio amateurs and CB-ers are familiar with this phenomenon, and it's effects, including (the curse of) VSWR.

A somewhat odder effect also occurs, and that is dependent upon the length of the cable. This is particularly noticeable when you have a tee wiring arrangement.

With this arrangement, there is an unterminated length of cable hanging off the splitter ("twofer", to use that great Americanism), and this can cause all sorts of problems. The technical term for this bit of wire hanging off the main bus is a "stub". With just the right length of cable, that stub becomes effectively a short circuit at just the right frequency. Thus although the circuits all check out OK with your multimeter, when DMX is flowing, all sorts of inexplicable odd things happen.

For more info on the DMX-512 protocol, look here: http://www.dmx512.com/web/light/dmx512/index.htm

[smokeAndMirrors]

Thanks Matt - and everyone - for your input.

[BigchainEvents]

Althow it happens to everyone if you have experience and don't get nervous you can at least isolate the problem. In order to do that you must have time to test i a calm environment. That being said i think your problem was lack of time. I usually prefer to arrive sooner than everyone, setup my gig and then have a couple of boring but relaxed hours compared to the risk of not bring the money or have a heart attack. If you think you don't have enough time to setup your gig with a safe margin don't accept the job, if clients want you they will make room for your needs.
Another issue are the equipments and cabling: you should consider the products that are reliable otherwise you will have problems. Try to understand what are the industry standards and stick with them. Invest in a good set of cables (110 H) and respect the DMX rules.
For last, power. Voltage variations can make stuff go crazy and even if you test it right in the afternoon when the show starts might be more electric devices connected messing up the current, so buy a voltimeter and check. If you work in problematic area consider a voltage stabilizer. Don't load power amps or conventional lights just regie equip and robots.

[mnoethlighting]

And try to put your sound and light gear on different circuits if at all possible (at least have them plugged into different outlets).