Flicker

[Jesse Crooks]

A theater where I fill in as a projectionist has been experiencing a serious flicker on both projectors. The flicker dances around the screen like you'd see with a failing lamp, but the lamps were well under their expected lifespan (although they were, of course, many years old), and they replaced the lamps this week which I've been told did not solve the problem. The booth is inadequately cooled, but they only added a split unit for AC with the digital install (which is still inadequate to cool the booth) so inadequate cooling is unlikely to have manifested as a new problem. Since the lamp change did not resolve the issue, I guess we're looking at a rectifier issue. I was under the impression that rectifier issues would manifest differently than lamp issues (ex., a pulsing flicker at a set frequency caused by a bad diode rather than the dancing flicker you get from an erratic arc). Please correct me if I'm wrong.

Super Lume-X, Christie 2kW lamps, Strong FXPS-20 rectifier

And suggestions as to what the cause could be?

[Jim Cassedy]

The Super Lume-X's, like many Xenon lamphouses, usually have either a bar magnet or
sometimes an elecromagnetic coil, usually mounted somewhere under the bulb, often near
the reflector, to stabilize the xenon arc. I've seen unstable xenons caused by the magnet
being knocked out of place, or put in backwards (wrong polarity) after being taken out for
some reason. The puzzling thing is that you say this is happening on both lamphouses.

You mention possible overheating. I would think that magnets designed to be used in
close proximity to a xenon bulb would be engineered to withstand high temperatures,but
any magnet can be weakened, or totally lose it's magnetic properties if heated above a
certain temperature. ( The "Curie Point" -which varies by what the magnet is made of)

This may.or may not be your problem, but I've run into flicker caused by a bad
'arc stabilization magnet' on several occasions. It's something to think about.


The Bar Magnet Inside A STRONG
HIGHLIGHT II Xenon Console)
Magnet_2.jpg

[Jesse Crooks]

It was a problem that arose within the last year or so (it was present when I worked there in June, but not when I worked there in 2022), and the lamps had not been changed in the meantime so it's unlikely that meddling with the magnets caused the problem.

[Randy Stankey]

Have you checked for lamp alignment or focus?

That would be one of the first things I would look at, especially after the lamp has been changed.

[Tony Bandiera Jr]

Check all power supply connections in the rectifier and make sure they are tight. Check diode pigtails for signs of overheating. It is possible you have multiple diodes failing which can cause very erratic output. Check for excess ripple on the DC output (AFTER lamp is lit,) use an AC voltmeter. Anything higher that a few volts is bad, meaning diode(s) or filter caps are bad.

If the power supply checks out ok, have an electrician inspect all breakers and panels for loose connections or overheated terminals, starting at the booth panel and working towards the main service. I had one theatre many years ago have mysterious and random flickering issues, everything in the booth checked out. It was later found to be a bad main breaker, which was discovered when it went up in smoke.

Another chain theatre I serviced had a dry transformer in the booth electrical room go into full meltdown mode mid day, while I was there on a sound service call. Lost of fireworks, bad noises and loads of smoke. Worst part was fire dept wanted me to shut the building main off while the fireworks were going on, I refused and we had to wait till the power company shut everything down. (The main breaker in question dated back to the 50's and was always hot and smelled like it was burning. No way I was touching that.)

[Frank Cox]

I'm pretty sure I've told the story here before about the cooking hot day in August where I was running the Saturday afternoon matinee at the theatre where I worked before I had one of my own.

I walked down into the lobby to get a drink (and a break from the heat) and while I was there I heard a huge BANG! and saw a flash of lightning on the projection room stairs.

Raced up to see what happened and found the rectifier's transformer embedded in a hole in the wall.

I felt pretty lucky since the space between the rectifier and the wall is where I had been standing three minutes before....

[John Eickhof]

go with Tony on this also look for a low or missing phase if three phase, if the bulb is not running to normal current? what bulb size? what current? what voltage at bulb? low voltage or current will cause instability, diode or bad winding in 3 phase power supply? change of line voltage without changing ps taps ie: unit set for 120/240 3ph then trying to work on 120/208 3ph....if a brute force rectifier possible filter cap(s) failed....poor / overheated or scarred power power contacor...

[Tony Bandiera Jr]

go with Tony on this also look for a low or missing phase if three phase, if the bulb is not running to normal current? what bulb size? what current? what voltage at bulb? low voltage or current will cause instability, diode or bad winding in 3 phase power supply? change of line voltage without changing ps taps ie: unit set for 120/240 3ph then trying to work on 120/208 3ph....if a brute force rectifier possible filter cap(s) failed....poor / overheated or scarred power power contacor...

Good additions to things to look out for there old timer.

That rectumfryer is a brute force, looks a lot like LP Assoc. design as well.

Edited to add: We both forgot another: Look at the DC leads ends between the rectifier and lamphouse, and check inside the lamphouse at all DC connections, including the ignitor, shunt and both ends of the lamp.