Fault-Finding – Theatrecrafts.com

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Lighting systems can be complex. The following are designed to help you through finding what’s wrong and fixing it.

Lighting Console not working

Is the console display monitor turned on?
Is there a working power supply to the console?
Do you need to log in to get the console software running?

ETC Eos / Nomad
If the system is in ‘offline’ mode, make sure the Nomad dongle (USB) is present and inserted correctly. Restart the software if necessary.

Whole Rig not working

Is Grand Master up on lighting desk?
Is lighting desk on?
Is DMX connected correctly between the desk, dimmers and other DMX devices?
1. If the dimmer racks have a ‘DMX OK’ light, check that it’s on
2. If you’re using LEDs or moving lights, check that they’re receiving DMX correctly (there will be an indication that they’re receiving DMX on the display screen or using LED indicator lights).
3. Use a DMX Tester (e.g. DMX Cat from City Theatrical) to check the DMX signal is being received.
Is the rig patched correctly? Start simple – check one lantern on one dimmer that you can physically see is set up correctly. Check that the desk is set to transmit data on the correct protocol. This is important if you’ve been using the desk with visualisation software. To control a physical rig, DMX, Artnet or sACN should be selected depending on how your system is set up.

Moving Lights – No response from one unit, rest of rig working correctly

Moving Lights – No response from rig

LEDs / Moving Lights – Some fixtures are behaving erratically (flickering, odd movements)

Possible DMX fault. Check all DMX connections are sound, and add a DMX terminator to the end of the DMX run, to reduce the amount of interference on the signal.
Ensure you’re using only DMX cable, not substituting it with microphone cable (which sometimes works, but is not reliable).
Some lighting desks can produce a range of different DMX speeds, and some (older) equipment can’t keep up with the fastest, resulting in odd behaviour.
ETC have produced a useful page about DMX Speed and how it can affect equipment reliability.
For cheap LED fixtures, check that RDM is turned off on your console or DMX node. The fixtures are not able to cope with the RDM pulses, and may pulse when it’s received (regularly).

Generic Rig – Individual instrument Not Working

Check lantern is correctly & firmly plugged into rig
Check lamp in lantern (especially if it was working previously)
1. If the lamp seems OK, make an adjacent circuit ‘live’ on the rig, check that lantern works, then unplug it and plug in your faulty lantern. If it works, it’s a dimmer / connection problem.
If lamp had blown, check fuse / circuit breaker on dimmer rack – the circuit breaker usually trips when a lamp blows, especially if there was a bright white flash when it did so.
Is circuit from rig correctly connected to dimmer rack?
1. If the dimmer rack has sockets on the front of it, try cross-connecting the faulty circuit with a known working one.
Is the dimmer correctly patched on the lighting desk? (Soft patching)
Is the cable between the dimmer rack and the lantern faulty? (Try running in a temporary cable from the dimmer output to the lantern before you run it in permanently).
With an EOS (ETC) system, are there any parked dimmer channels? Check on the About page (keyboard shortcut Y) to see if it’s parked.

Generic Rig – Bar of instruments not working

It may be that a dimmer rack has tripped off, or has lost a DMX signal.
Also check that the cables from the bar to the dimmers is connected correctly.

Generic Rig – Instrument(s) flickering

If a number of lanterns are flickering in sync:
Possible DMX fault. Check all DMX connections are sound, and add a DMX terminator to the end of the DMX run, to reduce the amount of interference on the signal.
Ensure you’re using only DMX cable, not substituting it with microphone cable (which sometimes works, but is not reliable).

If a single lantern is flickering randomly:
Possible loose power cable (ensure it’s plugged in fully and firmly), loose plug to the rig, or loose connection in the plugtop.
Could also be a worn / damaged lamp base. Loose connections between the lamp and the lamp base may, over time, cause arcing, resulting in deposits of carbon (blackening) in the lamp base, resulting in a poor connection. Many lamp bases can be replaced (seek advice from a competent person).

DMX Problems

DMX cable should be used whenever possible, rather than microphone cable.
The DMX run should be properly terminated.
There must be fewer than 32 fixtures on each run of DMX, or less than 20 RDM fixtures.
The cable must not be ‘y’ split.

Additional information by Vincent A Sanchez

Blown Lamps

Lamps blow. It’s a fact of life. There will be some point when, half way through a show, you’ll notice something isn’t working that was working when you checked it before.
This is why the lighting operator needs to have a good sense of the rig and the show so that they can bring up an alternative lantern if something blows.

Lamp Life

Some commonly used lamps (UK) and their rated life:
T11 (1000W / 240V): 750 hours
T26 (650W / 240V): 400 or 600 hours depending on manufacturer

For a 750 hour lamp; If the show is 2 hours long, and you’re doing 6 performances per week, the lamp will last just over a year (IF it’s used constantly throughout the show, and is not flashing, and if it’s not used for rehearsal or other purposes).

Maximising lamp life
– Avoid turning a lamp on to full from cold. If you need to ‘snap’ a lantern on, try to preheat the lamp in the cue before so it warms up a bit.
– When checking lanterns are working correctly, fade in rather than turn on.
– Save lamp life by switching the lighting state off during breaks or as soon as the auditorium is clear at the end of the performance.
– Set the ON function of your lighting desk to 60% instead of 100% to reduce strain on the filament when flashing through circuits.
– Be gentle with the lantern when focussing or moving it, especially if it’s hot. Lamps are far more delicate when they’re hot, and filaments can be easily damaged by rough treatment.

Should you replace lamps as a precaution before they blow?
If you can easily measure the amount of time each lamp in your lighting rig is on for, then, in theory, you can ‘predict’ when the lamps will blow, and replace them before they do. However, lamp life is not an exact science. (see box on the right for tips on maximising lamp life).
Like a lightning flash signalling an imminent thunderclap, there’s often a brighter light output from a lantern just before the lamp blows. The reason for this is easy to explain – the filament is made up of a delicate coil of wire which is suspended from a few thin wires. If the filament is shortened (because the supporting wires have broken or other physical damage), the current flowing through the filament increases, producing a brighter, whiter light. This obviously can’t last long – it could be a few minutes, but the lamp usually lasts until just before you turn it on for that important moment during the show. Once the lamp has achieved it’s brightest state, it usually blows completely when you turn it off and on again. Whatever happens, when you see the bright white light suddenly appear from a normal looking lamp, it’s time to replace it.

Blown fuse / circuit breaker

When the lamp does finally blow, it’s often a bright white flash as the filament short-circuits.The resulting high current flow may be enough to blow the fuse (or circuit breaker) in the dimmer, so if the lantern still doesn’t work after changing the lamp, that’s the next thing to check.

How to change a lamp

The first step (always) is to prove the lamp has actually blown. Turn on an adjacent lantern, check it works correctly, then cross-plug the suspect lantern into it’s supply socket. If the suspect lantern still doesn’t work, you’ve ruled out the cabling, dimmer, and fuse. Almost.

Now unplug the faulty lantern. Don’t just rely on your colleague turning the lantern off on the control desk. If the lantern has a removable mains lead, unplug that also, as many lamp access trays can’t be opened until that has happened.

Once you are certain the electrical supply has been physically disconnected, open the lamp access door. The exact method of doing this varies according to the type of lantern, and may require a screwdriver. Below are shown some methods of accessing lamps:

COMING SOON – VIDEO

If you’re in any doubt about how to gain access to the lamp, refer to the manufacturers instructions.

IMPORTANT NOTES:

There’s a danger a damaged lamp can explode – ALWAYS handle with gloves and wear eye protection when changing lamps.
Allow at least 15 minutes for a hot lamp to cool before touching it, and always use gloves as an extra precaution.
Only handle a lamp (old or new) by the ceramic base.
Ensure that you don’t touch the glass of the lamp (the “bubble”). Any marks that are made on the glass from greasy fingers can cause that area of the glass to heat up at a different rate from the rest of the bubble. This can lead to a bulge in the glass and in extreme circumstances can cause the lamp to shatter. It will almost certainly lead to premature failure of the lamp. Most manufacturers supply the lamp in a protective plastic envelope which should be used until the lamp is firmly seated.
Make sure you remove the plastic envelope before turning the lantern on again!!
Once you’ve replaced the lamp, be sure to check the fuse in the dimmer as it’s possible the fuse has blown (or the circuit breaker been tripped)

Written by Jon Primrose, May 2017
Updated June 2024
Additional information by Vincent A Sanchez

Keywords: Troubleshooting Lighting, Fault-Finding Lighting, how do i repair a theater lamp if there is no fuse, theatre lamp fuse, repairing theatre lamp fuse, diagnosis of a theater lamp