Fault-Finding

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

Whole Rig not working

  1. Is Grand Master up on lighting desk?
  2. Is lighting desk on?
  3. 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

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

 

Moving Lights – No response from rig

 

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).

Generic Rig – Individual instrument Not Working

  1. Check lantern is correctly & firmly plugged into rig
  2. 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.
  3. If lamp had blown, check fuse / circuit breaker on dimmer rack
  4. 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.
  5. Is the dimmer correctly patched on the lighting desk? (Soft patching)
  6. 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).

Generic Rig – Bar of instruments not working

 

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).


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 she/he 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
There’s a danger a damaged lamp can explode – ALWAYS handle with gloves and wear eye protection when changing lamps.

IMPORTANT NOTES:
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)