Xenon Projection Lamp Flickering

[Repeater]

Hello all, we have a Christie HD18K projector. It, of course, has a xenon lamp in it. Lately, it seems to be flickering, varying in output, very much like an old movie on the big screen does. Actually, it always has done it to some degree (barely noticeable), but seems to be getting worse (or maybe we're starting to over-think it...). We rented three 30K projectors last spring that did the same thing to varying degrees, so it's not just our lamp or projector.

Ours now has 500+ hours on it, with a rated life of, I believe, 750 hours. Is increased flickering a symptom of a lamp getting up in age? Thanks!

 

[ruinexplorer]

You may want to look at increasing the power to your projector with a buck/booster. This hasn't been a problem with the newer models like it used to be, not to say that it can't happen. In our rental stock, we would provide a buck/booster with each of our projectors, since we wouldn't know what the power would be like in each of the venues where the projectors would be used.

If you hadn't had the same problem with the other projectors, I would guess that you possibly had a bad lamp. But yes, you are correct with the lamp life.

 

[Footer]

Check your power coming into the building as well as check your ballast. Do you ever have audio guys complaining of bad power?

 

[porkchop]

I'm going to second Footer's mention of ballast. I haven't worked or Christie's, but I have worked on a few different arc lamp units and in my experience flickering lamps are usually a ballast problem not I lamp problem.

 

[Repeater]

By "increasing the power" do you mean voltage? The voltage at the projector measures 208 +/- 2 volts or so.

Another poster suggested "checking the ballast". What do you mean by that? Are there taps on it to compensate for various voltages at the projector?

Being a licensed electrician, I can verify that the the overall condition of the electrical system in the building is extremely good. And the audio guys never have any problem with "bad" power at all.

So what I'm gathering is that xenon lamps DO flicker more as they age, is that correct?

 

[Footer]

The ballast is the power supply that drives the lamp itself. On older projectors like the ones I have in my building, they are large external units that weigh more then a Volkswagen. I have no clue on the newer projectors how the lamp is powered an all that fun stuff. If in doubt, call Christie. However, any time you have a discharge lamp flicker its either ballast, power, or lamp. If you have a spare lamp, swap it out and see what happens. That will at least get rid of one variable.

 

[FMEng]

By "increasing the power" do you mean voltage? The voltage at the projector measures 208 +/- 2 volts or so.

Because the issue is likely voltage drop, be sure to measure it under load with all other major loads running as they would during a show. Open circuit tells you nothing.

 

[ruinexplorer]

Yes, I meant increasing the voltage. Since you have the same issue with rented projectors as well as your own, I would doubt that it was an internal issue such as the ballast. Also, since you are having the issue on multiple units, I would also doubt a lamp issue. Since you are a licensed electrician, you should have no problems upping the voltage with a buck/booster. This procedure was actually recommended by Christie technicians well over five years ago. It has to do with build up of deposits on the arc leads when there isn't significant power to burn them off.

If your projector is not permanently installed, it also can help if you rotate the projector position from table to ceiling (upside down) on a regular basis. This will also help since the deposits on the leads sag.

 

[derekleffew]

Unwanted/undesired flicker in xenon light sources is the bane of my existence when working with video; the human eye is much more tolerant and forgiving.

Something from the attached PDF may help:

An unstable arc, othe the other hand, is a much more complex problem. There are several things that can cause these phenomena, both within the bulb and within the lamphouse. Let's examine the most common ones: ...

For xenon globe s used in followspot s, it's standard to rotate the lamp 90° at regular intervals. This may not be possible on a projector if/when the lamp is factory-mounted in a cartridge or carriage, thus ruinexplorer's suggestion to turn the entire projector over.

View attachment XENONFAILURE.pdf

 

[Repeater]

Well I checked the voltage at the projector while house and stage lights were on, and projector operating--205 volts. Seems well within the voltage specs for this box. Should I still consider boosting the voltage?

The posted PDF was very interesting too. Thanks for posting that.
Next week I plan on switching to our spare lamp. That will tell us a lot. I hope this lamp isn't "done" already, it only has 560 hours on it.

I may also call Christie support for their suggestions. I will post any updates.

 

[ruinexplorer]

Yes, I would boost about 10v if your operating voltage is 205. It is within specs, but that doesn't rule out internal voltage drop. Definitely contact Christie support since the lamp may still be able to be pro-rated if they determine that is at fault. I only recommend the boost because you said that you had a similar issue with rented projectors.

 

[Repeater]

I contacted Christie support and received a same-day reply.

According to Bill there, increased flickering is a characteristic of an aging lamp. He said that Christie did not recommend increasing the voltage to the projector because he said it wouldn't help. (I'd still like to try it anyway...)

I also may try inverting the projector to see if that helps.

As for the three rented 30Ks we had, we probably had an old lamp or two there also (I didn't check hours on those lamps). And on those boxes, there's an Auto Lamp function (something like that) that will optimize lamp focus, plus a function to compensate for ballast-to-lamp cable length. (I can't remember if we ran that or not).

Again thanks for the help.