DMX Problems
Sun, 6 Nov 2011, 10:35 amjeffhansen15 posts in thread
DMX Problems
Sun, 6 Nov 2011, 10:35 amHELP!
Down at Melville Theatre, we seem to have a ghost in the machine.
The lighting rig is quite simple - A Jands ESP II desk, and two 12 channel Jands GP12c dimmer racks.
The problem is intermittent. When we go to black, and then try to bring lights up, one or the other of the racks doesn't respond. The DMX light on the rack goes out, and the STATUS light flashes (with a 0.1 second period, about).
If we then cycle the 3 phase supply to the dimmers, everything springs back to life. The fault doesn't happen every time. If we don't go all the way to black, the problem doesn't seem to occur. When it happens, sitting by the dimmer, I hear it start to ramp up for half a second or so, then it crashes.
What we have tried -
- Rented a replacement desk, also an ESP II, with no result.
- Rented a dimmer rack - The rental rack has not yet failed to respond, but still have issues with whichever of our Jands dimmers we plug in.
- replaced our DMX cables.
The Jands dimmers have built in terminating resistor, which we are making sure is switched on at the final rack. The racks are correctly addressed.
All the power supplies involved originate from the same switchboard.
Today, I'm going to run the desk powered from an isolation transformer, in case it is an earth loop issue in the DMX cable.
If that doesn't do it, I'm going to rent another dimmer rack and see what happens.
Any ideas?
We have had this problem for a long time, though it seems to come and go.
jeffhansenSun, 6 Nov 2011, 10:35 am
HELP!
Down at Melville Theatre, we seem to have a ghost in the machine.
The lighting rig is quite simple - A Jands ESP II desk, and two 12 channel Jands GP12c dimmer racks.
The problem is intermittent. When we go to black, and then try to bring lights up, one or the other of the racks doesn't respond. The DMX light on the rack goes out, and the STATUS light flashes (with a 0.1 second period, about).
If we then cycle the 3 phase supply to the dimmers, everything springs back to life. The fault doesn't happen every time. If we don't go all the way to black, the problem doesn't seem to occur. When it happens, sitting by the dimmer, I hear it start to ramp up for half a second or so, then it crashes.
What we have tried -
- Rented a replacement desk, also an ESP II, with no result.
- Rented a dimmer rack - The rental rack has not yet failed to respond, but still have issues with whichever of our Jands dimmers we plug in.
- replaced our DMX cables.
The Jands dimmers have built in terminating resistor, which we are making sure is switched on at the final rack. The racks are correctly addressed.
All the power supplies involved originate from the same switchboard.
Today, I'm going to run the desk powered from an isolation transformer, in case it is an earth loop issue in the DMX cable.
If that doesn't do it, I'm going to rent another dimmer rack and see what happens.
Any ideas?
We have had this problem for a long time, though it seems to come and go.
David AshtonSun, 6 Nov 2011, 03:50 pm
almost certainly a control
almost certainly a control wire problem, if I can fix it the charge is $150, if not, nothing.0428915820
just to elaborate, dmx runs at high frequency so testing cables with dc does not give you a true impedance measure, you need a proper dmx tester, if the line impedance is too high you will get intermitant signal reception, the Jands output is often rather low so a dmx booster at the desk may fix the problem if changing the cable is impractical.The control earth at the dimmer can be disconnected to remove earth loops, but an earth loop would not cause the dmx sensor light to go out but give you a confused signal, not no signal.The termintion resistor is to stop reflections going back down the line and false trigger other units in the chain, but you have no other units in the chain so switching off the termination resistor may increase the gain at the dimmers and solve your problem.
jeffhansenSun, 6 Nov 2011, 06:53 pm
We've replaced the cable
We've replaced the cable with twin pair twisted shielded instrument cable, to no effect.
But I'm happy to take you up on your offer. I'll be in touch tomorrow.
By the way, the isolation transformer didn't help.
www.meltheco.org.au
jeffhansenWed, 9 Nov 2011, 09:47 pm
OK.Hopefully, David and
OK.
Hopefully, David and Don have got the problem identified, if not fixed.
It seems the Jands GP12 dimmers are quite sensitive to a high supply voltage. This is one of the faults that will cause the STATUS LED to flash. Tonight, the voltage was measuring up to 252 Volts, phase to neutral, and about 440 phase to phase.
The supply voltage in an area can vary quite widely, depending on how Western Power have their system set up, and how much load is on the system at the time. Also, how far you are from the nearest transformer will affect how your voltage is affected by loading. The further you are, the more the voltage will fall away as load increases. Consequently, if you are at the end of the cable, your voltage can rise quite a lot when demand falls.
I've never measured the voltage at the theatre before, so have no correlation between the voltage level and whether the dimmers were working or not.
We have substituted 2 dimmer racks that are not sensitive to this over voltage, and it all seems to be working OK. We also took the opportunity to have those nasty exploding Jands capacitors changed out.
So now, I will need to ask Western Power to decrease the voltage in our area.
Or
Buy a couple of transformers to decrease the voltage.
Alternatively, we could trade in the dimmers and buy a couple of newbies. First, Let's run the rest of Mousetrap and see what happens.
www.meltheco.org.au
JoeMcWed, 9 Nov 2011, 10:48 pm
At the time I remember
At the time I remember relating a similar story about a large Boarding Schiool in Guildford. Where at mid afternoon on every Friday, the Midland Railway Workshops would shutdown early in the afternoon for the weekend. Subsquently when the Bording School fired up for meal time, most of thier electric elements in the food equioment, would glow cherry red, although they were 20 whatt density sheathing & blow the elements. This came about because the school switched on virtually when the Workshops wound down for the weekend. The SEC at the time rerouted the suppy & solved the problem.
I believe I mentioned at the time that this could be a similar problem at Melville.
jeffhansenSat, 12 Nov 2011, 09:02 pm
No more problems as
No more problems as yet.
I've reported the over voltage issue to Western Power (on Thursday), and they had someone on site on Friday. I have been told they will need to log the power quality in the area over a period of time, before they make any changes.
www.meltheco.org.au
JoeMcSun, 13 Nov 2011, 07:35 am
Lets hope it works!From
Lets hope it works!
From memory I think that was what they said last time? I think it is possibly thier standard 101 excuse for duck shoving it onto the back burner! At least it was the aude SEC mantra! Which is probably different with the new regime of Western Power?
It would be great if they could furnish you with their monitoring readouts!
jeffhansenSun, 13 Nov 2011, 09:01 am
Joe, I think in the long
Joe, I think in the long run, we might be better off trading in the dimmers on a new set.
www.meltheco.org.au
David AshtonWed, 7 Dec 2011, 08:44 pm
Australian standard voltage
This is a relevent thread from ALIA which explains the various voltage situations, there is a further link in it to each states local regulations, ironically all these bodies demand that contractors abide by Australian Standards, but none of them do.A case of "do as I say, not as I do"
For every complex problem, there is a solution that is simple, neat, and wrong.
Robert J WhyteThu, 8 Dec 2011, 06:01 am
Hate to say this, but the
Hate to say this, but the voltage was running at 252 volts 15+ years ago, we used to have problems in the old bio box and it was tested then.
The more things change the more they stay the same.
Cheers
Rob.
jeffhansenThu, 8 Dec 2011, 07:55 am
Had a call back from
Had a call back from Western Power yesterday.
They had a faulty Voltage Regulator in the switchyard which automatically changes tappings on load as required, or so I was told.
Our voltage was measuring at the top end of the allowable range (240V ±6% = 225.6 - 254.4 Volts). I'm sure he said we were up to 256V which is outside the range.
I'll take a look when I get to the theatre on Saturday, and see where we are at.
www.meltheco.org.au
David AshtonThu, 8 Dec 2011, 11:00 pm
At the very least its a relief to know what the problem is,
Now when you have this problem you know where to look, a intermitent fault with no idea what is causing it, makes everyone very tense, and can cause a lot of expense changing gear which is perfectly servicable, in this case the dimmers may well be shutting down because the voltage was in excess of the legally required voltage, which has other safety and lamplife implications.
For every complex problem, there is a solution that is simple, neat, and wrong.
JoeMcSun, 18 Dec 2011, 05:00 pm
You could always revert to
You could always revert to aude "water dimmers" [P*ss pots].
I cut my teeth on these back in the 50"s in NE pohmyland.
http://www.compulite.com/stagelight/html/history-5/salt-dimmers.html
Also made up a more primitive set back yem in N'castle [Pohmyland}, Which were efective & worked well. But they effected the local street lights & I got into more strife than Ginger Meggs!
jeffhansenSun, 18 Dec 2011, 06:24 pm
Joe, I think there might be
Joe, I think there might be some OHS issues with those. We use the same thing at work to load test three phase generators.
You can still buy a version of this for starting large electric motors. It uses the same principle of reducing the voltage to the motor to give a low starting current. A motor drives the probe into the liquid to increase the voltage, and the starter is finally bypassed by a contactor to give full voltage supply.
So, the story has a happy ending. I got a call from the Western Power tech last week, to say that they have tapped the transformer down, and reduced our voltage to within acceptable limits.
www.meltheco.org.au
JoeMcMon, 19 Dec 2011, 07:25 am
Lets hope this rectifys the
Lets hope this rectifys the problem!
I'm sure the relevent State Gov Minister wiill offer a months free power supply as compensation! 
But I wouldn't hang by thumbs waitung for it!