Help!

[jon1728]

Hi, this is my first post and unfortunately I have to start with a plee for help, this is the situation so far:-

 

At work the controller is a Pearl tiger, from which 3 lines are coming out,

 

1 going to a dimmer pack,

1 running to a set of lights above the stage (4 led moveable washes + 2 Dj lights)

& another which is basically going to the rest of the rig:- 2 trusses worth of LED's (about 8) moving heads (3) & another set of LED's which we use as the house lights (about 10 or so)

 

The problem that keeps happening is that when everything is powered up it works fine, I don't encounter any problems but if I leave it for a while once half of line 3 (the one with the most on it) at first just gets the occasional flicker, then it will become more frequent. After a while though it goes completely haywire, everything turning on and off, changing colour, movers flashing around changing direction. Sometimes this will last a while, other times it will resolve itself a bit sooner.

 

Now obviously this is a bit of a problem :)

 

I've been currently working at the club now for about 2-3 months so still trying to figure out exactly what's going on when it was wired up at the install. What I've tried so far is getting terminator plugs in to the ends of both of the non-dimmer lines. I've gone up to the cable in between the light that works and the one that doesn't and tried wiggling that about to see if there's a loose connection but that doesn't trigger it.

 

If anybody has any suggestions I would be most grateful. I come from mainly a sound background and although I'm happy running the desk and programming different states and whatnot I am really struggling with trouble shooting this.

 

Power problems maybe? or problems in the DMX line?

[Brian]

So the line with the problem is the line with the 8 LEDs, 3 movers and house lights?

 

You say 'half' the line starts to misbehave. Is that a random selection or is it, say, the units furthest from the desk (ie the 'second' half)?

 

Also, what make and model are these units?

[jon1728]

Hi Brian thanks for the quick reply, the lights that play up are always from a specific point onwards (and it's the furthest half of the line away from the desk) I'll get exact models over soon but know that most of what we use is proline.

[harrydir]

I've had a very similar problem - possibly the same night-club! - which turned out to be a fixture misbehaving. It was an LED moving wash, after an unspecified amount of time it would spit out random data and corrupt the rest of the line. I'm not saying its your problem but I would pull the fixture out of the chain next time you're in and see if you still get it.

 

Problems like this are annoying to fix as they happen randomly and inevitably not until the middle of the final DJ set or something, so not ideal for fault finding, but just remember what you've done and keep trying!

[Brian]

...and it's the furthest half of the line away from the desk...

My first thought on reading your post was that the unit at the halfway point is going into Master/Slave mode and sending its own data to the further units.

[dbuckley]

Harry beat me to it!

 

However I don't quite agree the diagnosis, but ultimately that's just detail, because if you remove this fixture from the chain and the fault goes away that is a result.

 

My slight difference of opinion is that on many fixtures the in and out sockets are simply daisy chained internally, and so if the fixture somehow goes bananas and starts transmitting junk then it should corrupt the line fore and aft of the fixture, and you know which fixture is where the problem happens, so it can't be the whole chain. In addition, many fixtures can't transmit ever, as the DMX transceiver chip has the transmit enable pin hard wired off, as transmit will never be needed. At least not until RDM and master/slave modes appeared.

 

However, some fixtures regenerate the DMX signal rather than simple daisy chaining, and so the chain "begins again" at any such fixture. If the data gets corrupted in the fixture, then it would be passed on as corrupted to the next and subsequent devices.

[Don Allen]

If you can get to the fixtures when the fault is occurring, bypass the fixtures one at a time by plugging the DMX cable into itself, starting from one less than half way, then work your way along to the end. If it is still occurring after they have been bypassed, turn the fixtures off in the same sequence as the interference may be coming out via the mains from a faulty switch mode power supply.

[timsabre]

My slight difference of opinion is that on many fixtures the in and out sockets are simply daisy chained internally, and so if the fixture somehow goes bananas and starts transmitting junk then it should corrupt the line fore and aft of the fixture, and you know which fixture is where the problem happens, so it can't be the whole chain. In addition, many fixtures can't transmit ever, as the DMX transceiver chip has the transmit enable pin hard wired off, as transmit will never be needed. At least not until RDM and master/slave modes appeared.

 

This is DJ kit though, it all has master-slave and can therefore transmit. And a lot of the cheaper end stuff is notorious for randomly going into transmit mode when it shouldn't. On some fixtures you can disable standalone mode which is a good idea if you have a console.

 

You would think that fixtures with in and out linked through would corrupt the line both ways, but in fact I have seen it happen where it only corrupts the "downstream" direction, or only affects a number of fixtures in the vicinity of the problem fixture and not the others. Presumably this is down to how "strong" the driver chip in the fixture is, compared to the console/controller.

[mac500]

It could be one dodgy bit of cable. If you can work out from which fixture it goes wrong from then you should hopefully be able to eliminate the rogue cable b

[jon1728]

Thanks for the input so far guys. In answer to the earlier question :-

 

x3 prolight imove 250 spot (There was 4 but one of them has been taken down from before I started)

x8 prolight 3 watt LED par cans (can't find the exact ones online but this is the description that's on the clubs tech spec)

 

not got the info on the other led lights on there but I'll find out tonight when I'm down there!

[jon1728]

Okay so the one that was causing the problem seems to be this puppy:-

 

http://prolight.co.uk/DJ/item.php?id=508910

 

I went up and bypassed each one from where the error started to occur. What's weird is it only seemed to resolve itself when I bypassed the one which was 1 after where the fault started (implying it was transmitting weirdness downstream to the rest of the fixtures and also 1 fixture in the opposite direction)

 

So far I've had to bypass the 3 that were on the same DMX address so after tonights show I'm going to try putting the other 2 back in (one at a time) and see if it is just the one fixture that's playing up.

 

Does that sound about right to you guys?

[indyld]

Be aware that sometimes fault finding DMX issues on site can appear to be one thing initally, then the other, and verifying them isn't always straightforward.

 

An issue with a particular cable can only appear when you add fixtures downstream, even though the issue is further up. Sometimes starting at one end adding and removing fixtures or cables can seem to point to a particular part of the chain although the fault isn't actually there. I've traced plenty of faults that at first attempt, seemed to be somewhere else. The puzzling ones that move around are statistically higher in the "one-legged cable somewhere" category. A terminator can help amplify the problem, as can removing any buffers which can mask issues by still managing to send out an apparently working signal even though it's a complete mess.

 

Fault Finding DMX Problems

[bigclive]

I went up and bypassed each one from where the error started to occur. What's weird is it only seemed to resolve itself when I bypassed the one which was 1 after where the fault started (implying it was transmitting weirdness downstream to the rest of the fixtures and also 1 fixture in the opposite direction)

 

It could well be that it was having some "master/slave" issues and actually spitting data back onto the DMX network. There's a lot to be said for dumb DMX fixtures that can only receive. All it takes is one rogue light capable of transmitting data (RDM!) that has a software bug or crashes and it can cause all manner of issues.