Originally, the complaint was that the lamp had failed. It was lit and a show was running. The failure occurred in the middle of the presentation.

That lamp was only installed in April or May of this year, so this all seemed very strange to me.

I replaced the lamp with the same model (PerkinElmer 2000HTP). The "pointy" electrode of the spent bulb looked like it had bits missing; not the usual pattern of erosion that I see when I pull old bulbs out of these machines.

The new lamp strikes up immediately but there is a very noticeable flicker. The quality of the light is a nice, bright white, but the flicker is out of control.

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The end caps will change colour if they are getting too hot, starting off as a light straw and then blue depending on how hot they are getting.

Check the contactor and make sure that it's contact areas are clean so that all 3 phases are getting through it they can become intermitent. Also if there is any current selector switch check them as well for corrosion and pitting

-Aaron

You can probably eliminate (or confirm) diodes as the problem by starting with your current meter. If it's running at its normal level, diodes are probably not the culprit & you can look elsewhere.

If you have low current, or if you notice the flicker on the screen but not in the light behind the projector, then it's probably a phase loss, which can be anything from the incoming power line, through all of Gordon's list.

While you're checking, be sure to look at the secondary lines from the power transformer & all subsequent connections. These high-current connections can work loose (or burn off), and aren't always easy to see. However, a burned connection will cause the same problem as would an open diode, bad contactor, or missing primary leg.

If you have a power company problem, you should be noticing other dead equipment in the building... unless you have a 3-phase service feeding only that lamp & you were fortunate not to have one of the other 2 legs go out.... but if you have to check your breaker, this would be easy to confirm, one way or the other.

If a doide went south or you lost a phase, the strobing flicker will be accompanied with a bulb current much lower than normal.

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Remove all the diodes and test each one. Replace any bad ones. In my experience (though somewhat limited), a flicker is either caused by an old or bad xenon bulb or a bad diode

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This is exactly what our service company recommended over the phone. There were several bad diodes -- definitely 2 are bad, possibly 4 (out of 6) Thanks for the help.

Below are notes on some of the other suggestions...

Aaron wrote:

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If it is a steady 12Hz flicker, then as suggested before, either one phase is gone or you have one or more bad diodes. (another indicator of the above trouble would be the current will be about 1/2 to 2/3 of normal)

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Yes - 12Hz flicker rate.
Yes - Low current (was 80A; dropped below 60A)

Paul and Jack also cued me to check the current on the bulb. Thanks to all for helping.

By the way...it's still not fixed...I'm waiting for the diodes to come in from Miami. I'll follow up as to whether the problem goes away.

How come one of my meters can't give me a reading on the forward diodes? The one from Radio Shack can read them all, but the Fluke one can only test the reverse ones.

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Steve