Flickering projector lamp - electricity problem? (1 Viewer)

[David Payne]

Hi, I've had an intermittent problem with what seemed to be a flickering lamp on my projector. I even started a thread about it here some time ago. After a few months of observing the issue, I'm less convinced it's a problem with the actual lamp/projector, so I've started looking elsewhere. My best guess at the moment is that the mains electricty supply may be going a bit "wobbly". This is partly from watching the patter on the screen and also because I've noticed some lights in the house are prone to doing the same thing. Has anyone else ever found any problems with things like this, or am I barking up the wrong tree? If it is a possbility, is there an easy way to establish for sure that this is the problem?

 

[Leo Kerr]

Okay, the common symptoms of ballast-lamp issues:

1. Arc instability. Is there a hot-spot in the image? Does it seem to wobble or wander around? (the hot-spot, that is.) Chances are good that this is a fault with the lamp itself.

2. Arc flicker. Can be ballast or lamp.

3. Does the fan slow down or speed up during this? It could be a main power supply issue or feed power issue (that is, your actual house power.)

Depending on what the main power is doing, the ballast and power-supply are supposed to help cover over voltage fluctuations.

It'd be nice if there were good and inexpensive voltage-event recorders; it'd take a lot of mystery out of power diagnosis.

Leo Kerr

 

[David Payne]

If by "hotspot" you mean an area that's brighter than the rest of the image, then no, I haven't seen anything like that. I haven't noticed the fan doing anything differently, but I'll check. Can you explain what you mean by ballast?

I should probably also point out, if it helps, that the flickering is very subtle (both for the projector lamp and other lights in the house that do it). Most people may not even notice at all.

 

[Leo Kerr]

Arc-type lights, be they mercury or sodium-based street lights, 7kw xenon projector lamps, or 150w metal-halides in a home projector, "look like" a dead-short to the real world.

So inside the projector is a "ballast" which is a current-limiting device so that your power-system sees your projector as a 200w load, rather than a 2400+ watt load that'll trip your 20amp breaker.

The ballast also "starts" the lamp. I'm not sure on the details as much for the smaller halide-type lamps, but, for example, the ballast in the Christie X5s we have at work do the following on start-up:

initiation pulse: 30k-volts of uhf AC at micro-amps of current to "break down" the gap between anode and cathode in the high pressure xenon envelope. This phase lasts for ~0.05 seconds.

boost phase: the most stressful phase on all parts. Right after the initiator fires, the major capacitor bank discharges in a controlled fashion, starting at 120v DC at something like 20amps, and over the course of about 1 second, adjusts the voltage down and current up to:

operation phase: where the lamp operates for the rest of the day. The arc is driven by 12v DC at ~80 amps (~1000 watts.)

The ballast is a key part of the projector in regulating what actually happens to the light, and is therefore (a) expensive and (b) vitally important, and a bad ballast can kill lamps faster than anything else.

But yes, as for "hotspot," that was exactly what I meant. They're not uncommon in movie-houses, and sometimes you can see them "walk" around the center of the image. The hot-spot itself is caused by two things. First, the cathode has worn a bit, so the brightest part of the arc is not in the exact focus of the optical system. The "walking" is caused by a variety of potential issues, and often shows a poor anode-point, and/or contamination in the atmosphere of the lamp, and if you could actually look at the arc lamp itself while it was running without blinding yourself, you'd see that the arc was literally "wandering" around on the cathode.

(NOTE: In an arc lamp, there is a "point" electrode, and a "target," electrode that looks like a blunt peg with a flat spot on the end. I believe I have the electrical terms of cathode and anode applied properly here, but I haven't looked it up this time, instead relying on my poor memory. The arc "jumps" from the point to the land.)

Leo

EDIT: forgot to reply to the other point, too: if it's sufficiently subtle, don't worry too much; it does sound like it's coming from outside of the projector. The most effective way to combat that sort of very-low-grade problem is with a power-reformer, but they're expensive and inefficient. (It's literally an electric motor, fly-wheel, and generator, all coupled together. There's no direct electrical connection between the power company and whatever you're running. But it does let you do good isolation, frequency and/or voltage conversions, and all sorts of other neat things. -LFK)

 

[Joseph Bolus]

An unstable arc in the lamp -- which is more likely the source of your problem -- can sometimes be rectified by simply running your projector in its "high power" mode for about two hours. This is assuming, of course, that your projector has two modes available and you normally utilize the lower mode in order to conserve bulb life.

 

[David Payne]

Leo, thanks for posting that info. It was all new to me, and I had no idea that the current limiting circuitry was either present or necessary. I'll certainly take it on board. The only issues I've heard about before are to do with the lamp temperature and cooling system. (And if it helps I think the term "cathode" literally means negative - as in the term "cathode ray" for a beam of electrons - so for a component, the part that connects to ground would be the cathode and the part that connects to the positive supply terminal is the anode.)


I'll try that and see what happens. I do use the eco mode on my projector constantly.

 

[ChrisWiggles]

Leo's help was excellent, I just wanted to add that it's not unheard of that projector lamps develop this issue by any means.

 

[Leo Kerr]

The embarrassing thing, of course, was Joseph's advice right after mine. I've done that (at home. Come to think of it, I've done it at work, too); I forgot about it entirely. It's good advice and generally doesn't "cost" anything.

As for ballasts in lamps, they're not uncommon. Compact fluorescents, regular fluorescents; they, too, have current-limiting ballasts.

Leo

 

[David Payne]

I know it's been a while, but I thought I'd update you on what happened. I did try running in full mode for a few hours, and it made a difference. The flickering still appeared now and again, so I repeated the process, and haven't seen it since. It's been quite a while now, so I'd guess it worked and the problem seems to have been fixed. Now I know how to deal with it if it happens again. Thanks for all the help!

 

[Leo Kerr]

Good to hear that the problem was a simple one for you. I find it all to easy to go gloom-n-doom - read, expensive.

Leo

 

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[bladesedge]

I had this problem too. Turns out it was a screen resolution compatibility issue. As soon as I reduced the resolution on my laptop to 1023x768 (recommended res for the data projector), the screen flickering went away.

 

[Gregg Loewen]

hi

Most likely not a resolution issue.

This was big problem with the Marantz s1 and s2 projectors. It was finally corrected with the s3 series (which is now 5-6 years ago).

 

[jennigirly]

I've finally found a great source for replacement projector lamps that's CHEAP!

I've been trying for the past few years to find a source for just the bulbs, not the entire assemblies. I've always thought is was ridiculous to spend $400 to $600 on a lamp when I rarely get more than 1,000 out of a lamp in calibration. Especially when most of the actual lamps are made buy Osram/Philips and have the stock number printed on the side of the lamp.

Well, I finally found projector lamps.

http://www.projectorlampsworld.com/

My current projector is an Optoma H78DC3. The replacement lamp assemblies run abour $370 plus shipping from any of the discount on-line sources. It runs about $400 from Optoma.

Interlight has the replacement bulb for just $199.50

Most lamp assemblies will come apart with just a few screws. You just have to make sure you do not touch the new bulb ANYWHERE with your fingers. The slight amount of oils from your fingerprint can cause a lamp to explode. Wear disposable glove and wipe down the exterior of the new lamp glass reflector with 90% isopropyl alcohol to be safe. DO NOT TOUCH THE INSIDE OF THE REFLECTOR GLASS OR THE LIGHT STUCTURE INSIDE!

At these prices I won't think twice about throwing away a lamp because it won't calibrate properly. And it should only take a few minutes to replace a bulb in the assembly.

I received my lamp yesterday via 2nd Day Air for just an additional $24 to Florida. Installed last night and will preform a full calibration over the weekend. Now that I know the comapny is legit. I'm going to order a spare bulb next week.



Thanks !