ojc123 Posted October 5, 2012 Share Posted October 5, 2012 Strand 200 Desk to Botex ME72 Demux to ACT6+ dimmers. This set up has started to gently fade up and down slightly about 3 times a second. It is perceptible on low settings but less so at full brightness. I'll call it flickering. So far I've had the sparky check the mains voltage. He assures me it's ok under load.Used the system with the old analogue desk and the flickering goes (which suggests the mains is ok.)Replaced the Strand 200 with a Behringer desk we have for emergencies/drama room use. Same problem.Tried Magic Q from the computer. Same problem.Used the Strand 200, the Behringer desk and Magic Q on some LED fixtures which show no flickering.Checked the resistance of the terminators and terminated both DMX outs from the Demux.Removed the DMX out to the LED fixtures so that there are only the dimmers attached to the DMX chain (which is terminated)I measured the demux output voltages (no load) to see if there was variation.(+/-0.1V). What sort of variation would I expect to cause this behaviour? I'm thinking now it must be the demux. I don't have access to a spare Demux. So, I'm asking if anyone can tell me if this is a normal fault with demux units (or this type in particular.) Other suggestions are welcome before I hire/buy/borrow/steal a demux to test my hypothesis. Link to comment Share on other sites More sharing options...
dbuckley Posted October 5, 2012 Share Posted October 5, 2012 This is a distinctly odd behaviour, and I don't see an obvious fault with the demux that would cause this. So I'm going on an oddball hunch. Could you humour me, take the little desk, and plug it direct into the demux, with no other DMX cables in or out connected. Does this artistic wave still happen? Link to comment Share on other sites More sharing options...
themadhippy Posted October 5, 2012 Share Posted October 5, 2012 could it be something saved in the internal memory or the "chase" running? Link to comment Share on other sites More sharing options...
dbuckley Posted October 5, 2012 Share Posted October 5, 2012 Aren't the inbuilt chase in these demuxes (which I've never used) fairly brutal affairs and thus would always be visible? Still worth checking though! Link to comment Share on other sites More sharing options...
ojc123 Posted October 5, 2012 Author Share Posted October 5, 2012 If you mean a single short known good cable from desk to demux then the "artistic wave" continues with or without terminator. I'll check for stored chases. It's not impossible that the kids have pushed random buttons I suppose. The kids are loving the analogue desk. It's the seat of the pants thing I think they like. Link to comment Share on other sites More sharing options...
ocfe Posted October 5, 2012 Share Posted October 5, 2012 Does the flicker happen in both of the following scenario's:1. When most of the lighting rig is on i.e. channels 1-24? 2. When only 1 or 2 channels are on and the rest off? Link to comment Share on other sites More sharing options...
ojc123 Posted October 5, 2012 Author Share Posted October 5, 2012 The flickering occurs equally with one light on or with all lights on. It is less noticeable when the lights are on full and very noticeable when the faders are set to 3-4ish. Link to comment Share on other sites More sharing options...
dbuckley Posted October 5, 2012 Share Posted October 5, 2012 If you mean a single short known good cable from desk to demux then the "artistic wave" continues with or without terminator. No change there then. Is this a new feature, or has this always happened? Has there been any electrical work done in the venue? Still have a theory bubbling under, but hoping its the chase. Link to comment Share on other sites More sharing options...
Don Allen Posted October 5, 2012 Share Posted October 5, 2012 How old is the demux and has it been left on for extended periods as the power supply capacitors may be drying out and you have ripple on the dc supply. Unfortunately a bench job with a cro or replace the electrolytic capacitors. Link to comment Share on other sites More sharing options...
ojc123 Posted October 5, 2012 Author Share Posted October 5, 2012 I won't be able to check the chase till this evening. A new single phase supply was put in recently. It feeds the dimmers, two sockets and the CCTV cameras. The cameras are on all the time. I have not tried the lights with the cameras off. The problem arose after the install. That's why I got the sparky in to check the supply. The demux is 4-5 years old. It predates this thread. It just tends to be left on because it's in an awkward position so the capacitor thing may be a possibility. Link to comment Share on other sites More sharing options...
Robin D Posted October 5, 2012 Share Posted October 5, 2012 I would suspect mains noise on the power supply to the Demux. Has that been changed? If not, has something been added to to the main feed that runs that circuit. Large electric motors for example can sometime deliver a low frequency modulation onto the power supply. Can you get the Demux onto a different clean circuit and see if the issue goes away? If its just started and the power feed is also new, your assumption that its a power issue is IMHO highly likely to be correct. The Sparky may be out of his depth with the demands of complex electronic systems for 'clean' power. Something I've experienced in the day job! Link to comment Share on other sites More sharing options...
dbuckley Posted October 5, 2012 Share Posted October 5, 2012 This is where I've been heading. You've got the lighting equivalent of a ground loop. The first guess at running the desk locally on a short cable was to try and break the loop. But it ailed because the loop was not at that "end". The sparky is unlikely to be of much help (yet), as the way he measures it, everything is fine. If a problem can be identified, then he may be able to fix it. There a possibility there is a naughty neutral / earth bond somewhere. How exactly is the power distribution between the dimmer supply and the demux supply? Is the demux in some local socket off one supply or distribution board, and the dimmers off another? The most liekly problem is that there is a voltage differential along the common conductor from the demux to the dimmers. You may even be able to measure it with a meter, and you may find a bit of heat in the control cable.... Link to comment Share on other sites More sharing options...
ojc123 Posted October 5, 2012 Author Share Posted October 5, 2012 A new single phase supply was put in recently.There are four 32A breakers for the four dimmers and a 120A* breaker to cover the whole lot. There's a breaker for the twin socket and a breaker for the CCTV cameras.The demux is plugged into a socket which comes off the distribution board which feeds the dimmers. The whole lot is within 1m of the distribution board. The supply comes from the Substation which is built into the School building. The stage lighting is the only CCTV and the twin socket are all that comes off that supply. I can try to see if there's a voltage drop. I'll report back. *I think, but can't remember. Break in the action. I've had a chance to investigate further.I don't think there are any chases stored. I've tested the potential difference between the common ground of the Demux and the dimmers. It is fluctuating between 3.5V and 4.0V. The potential difference between the grounds on the dimmers are of the order of 0.02V. The potential difference between the casing of the Demux and the casing of the Dimmers vary between 3V and 4V. The difference between all the dimmer casings is about 0.3V. Are these figures likely to be worth investigating? I need to be able to talk to the sparky like I have a clue. Wow! That's magic. It's just added to my previous post! Link to comment Share on other sites More sharing options...
Robin D Posted October 5, 2012 Share Posted October 5, 2012 I've tested the potential difference between the common ground of the Demux and the dimmers. It is fluctuating between 3.5V and 4.0V. ............ Are these figures likely to be worth investigating? Yes. It depends were on the dimmer curve but I would expect at the mid range that .5V difference would cause the effect you are seeing. After all, it's 5% of the the control voltage so it would naturally make a visible difference. Link to comment Share on other sites More sharing options...
Kazeja Posted October 5, 2012 Share Posted October 5, 2012 Have you measured the DC voltage coming out of the DEMUX? Bit fidly with D types but a couple of paper clips in the appropriate holes (0v and channelX) should give you decent test points. If this control voltage is fluctulating whilst the desk is sending out a steady(?) DMX, I would check the internal power supply caps. K Link to comment Share on other sites More sharing options...
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