Film-Tech Forum ARCHIVE: Replaced the bulb but screen still dark

my profile | my password | search | faq & rules | forum home

»	Film-Tech Forum ARCHIVE » Operations » Film Handlers' Forum » Replaced the bulb but screen still dark (Page 1)

This topic comprises 2 pages: 1 2

Author

Topic: Replaced the bulb but screen still dark

Richard Greco
Phenomenal Film Handler

Posts: 1180
From: Plant City, FL
Registered: Nov 2003

posted 05-20-2004 08:23 AM

I have a Century SA projector with a Lumex lamphouse. It was really dim compared to other projectors. New York Minute was really bright in another theatre but dim in this one. I had the bulb replaced yesterday. Mean Girls is in there right now. In the other theatre is was really bright. Now it is really dim.

Any ideas? I have only changed a bulb before, I'm not familiar with many other parts in the lamphouse.

| IP: Logged

John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 05-20-2004 08:37 AM

Lamphouse alignment and lamp focus would be the first suspects. Is the lamp operating at the correct current? (Ammeters have been known to go out of calibration [Roll Eyes]

). Has this screen always been dim? Do you have a screen luminance meter to measure the screen luminance and uniformity? When the lamp was replaced yesterday, did they check focus and alignment, and clean the reflector while they had the lamphouse open?

http://www.kodak.com/US/en/motion/newsletters/pytlak/spring98.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/march2000.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/june2000.shtml

http://www.film-tech.com/manuals/STRSLX.pdf (note alignment procedure and maintenance)

| IP: Logged

Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 05-20-2004 08:55 AM

Take the lens and aperture plate out of the projector, fire up the motor, strike the lamp and open the dowser(s). What do you see on the screen? The image you see on the screen should look like a giant "bullseye".

You should see a dark circle in the center surrounded by a bright circle of light. You might see faint streams of plasma radiating outward from the center circle. You might also see Saturn-like rings around the dark center circle. (Depends on the kind of lamphouse you have and how well aligned it is.)

The dark circle in the center should be pretty well centered at the center of the screen. It should be a well defined circle, not an oblong blob. It should be pretty well focused. The light coming out of the projector should be pretty evenly distributed around the circle.

If you don't see something like this picture, one of two things is probably wrong: 1) Your lamp needs to be focused inside the lamphouse. 2) Your lamphouse needs to be aligned to the projector. There are other things wrong but let's keep it down to one or two things for now.

If the lamp alignments is off, that's pretty easy to fix. It'll take practice but you can learn to do that. If it's the lamphouse itself, you're probably going to need some help with that.

Don't forget to shut the projector down in the reverse order you started it up in. Shut dowser first. Kill the lamp. Stop the motor. Restore lens & aperture plate.

| IP: Logged

Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 05-20-2004 09:17 AM

What kind of lamphouse do you have, how big is the bulb (watts), and what size is the screen? Have you ever been able to get "good" brightness on that screen? Is the reflector clean and undamaged?

Can you dig up any old service records for your theatre? Those often have brightness measurements listed on them and you can use those as a ballpark for what you "should" be able to achieve with that equipment.

| IP: Logged

Richard Greco
Phenomenal Film Handler

Posts: 1180
From: Plant City, FL
Registered: Nov 2003

posted 05-20-2004 04:25 PM

Ok, I took out the film gate (aperture plate & such), lens, and closed the dowser. I have a Strong Lume-X lamphouse. I turned on the bulb through the automation. I opened the dowser and the black spot in the center was more like a rectangle. It looked like Squidward's head in Spongebob Squarepants. I do know that the lanphose is REALLY forward on the projector. I dont know what the throw is. Can I still be helped?

| IP: Logged

Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 05-20-2004 05:52 PM

Probably a focus issue or a damaged reflector
Is this theatre always been dark though as it may have been a undersized lamphouse for the screen size from day one

| IP: Logged

Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 05-20-2004 08:20 PM

I concur with John and Gordon.

Check your current calibration. There is a possiblity you are under-powering the bulb. The bulb will not like that and in due time, the arc could become unstable.

Could be also the mirror may be of the correct f-stop.

| IP: Logged

John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 05-20-2004 10:00 PM

Almost every time I have been called to check where the operator said: "The brightness was OK before I changed the bulb, but it's very dark now" ... it turned out to be the bulb out of focus, because the base pin was not pushed fully into the socket.

| IP: Logged

Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 05-20-2004 10:07 PM

I think we're on the right track. Could be a focus issue or a problem with the lamphouse. I think the first thing that needs to be done is to verify that the lamp is in focus, or at least as well as it can be focused.

1) The lamp was just replaced. Whenever the xenon lamp is replaced the focus needs to be checked and adjusted if necessary.

2) Judging from the stories that Richard has told us before it's easy to imagine that the lamp has been replaced before without checking focus. He may have inherrited a problem from somebody else's tenure working in the booth.

Focusing the lamp isn't very hard. It just needs to be done right lest we have problems with film being burned or some other nasty things. I think you can do this if you study up first.

Download the manual from the archives here. Read it and compare the instructions with your equipment.

There's an adjustment mechanism inside the back of the lamphouse. On your model, I think it looks like a knob with some screws on either side. Generally speaking, you adjust the mechanism up or down, left or right until the dark blob in the middle is round. Then you turn the knob to move the lamp in or out until the light is bright and evenly distributed on the screen.

Once you think you have it right you buckle the lamphouse back up and give it another check. This time you do it with the lens and aperture plate IN the projector.

<<Warning! Shining light through a lens with no film in the projector can burn the lens! Only let it run like this for a minute at a time. Shut the console dowser and give the lens a minute's rest for every minute it's open.>>

Look at the light on the screen to see that it is bright and evenly distributed. There should be no "hot spots" or dark spots. The corners probably won't be as bright as the center of the screen but it shouldn't be very noticable.

If you think you have it licked, run some test film (old trailers) to give it one final check. Make sure the film isn't getting toasted from the heat of the lamp. If all is well, you are ready to rock!

Once you are satisfied that the lamp is focused right you can check the lamp current and other things.

I'm sure somebody else who has used Lume-X lamphouses every day will come along and tell you all the wrong things I told you. In the mean time, get some studying in. [Smile]

| IP: Logged

Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

posted 05-20-2004 11:33 PM

Yes, it has happened to the best and bravest of us - the fan goes out or is insufficient and the lamp cooks the reflector and itself. If you touch the reflector lightly and the surface coating comes off in tiny shiny particles like disco glitter, it is gone. Hopefully though it turns out to be an alignment issue. The reflector is more expensive than a bathroom mirrir.

| IP: Logged

Richard Greco
Phenomenal Film Handler

Posts: 1180
From: Plant City, FL
Registered: Nov 2003

posted 05-20-2004 11:34 PM

Thanks a lot guys. I'm gonna wait till next week to adjust that. I'm not gonna do it on a weekend. I'll wait till Monday or Tuesday.

| IP: Logged

Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

posted 05-20-2004 11:38 PM

Has it been mentioned before that it is never wrong to risk a look at the ampere meter to verify the lamp current is in the specified range?
You should perform these tests before the weekend since during the weekend, you can expect the most business!

| IP: Logged

Mike Pennell
Expert Film Handler

Posts: 150
From: Tucson, AZ, USA
Registered: Apr 2003

posted 05-20-2004 11:56 PM

As Michael said above, try to get it done before the weekend. A dim screen over the weekend is nothing but bad publicity. Focusing the bulb should take no more than 5 minutes [beer]

| IP: Logged

Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

posted 05-21-2004 12:03 AM

If I remember correctly in my old age, on the Lumex lamphouse you just open the back flap and have immediate access to the focus adjustment screws. Since it is completely mechanical, you also have immediate feedback and see if your adjustments change anything. It`s not like with an SLC console where you stand next to the console and with your finger on the autofocus button and hope that something changes because otherwise the focus assembly is stuck or broken and your working day will be noticeably longer.
Here is one more thing to check: has a lamp ever exploded in the lamphouse? If so, the reflector will have a lot of small dents which you see as dark spots on the screen (without the lens).

| IP: Logged

John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 05-21-2004 08:44 AM

Basic things:

1.The optical path is in perfect alignment from the reflector, to the lamp, to the film aperture, through the lens, to the center of the screen image (string or laser alignment).

2. The distance from the reflector to the film aperture is set to specification.

3. The lamp is mounted correctly, with the proper spacers or adapters if needed.

4. The reflector is in good condition and clean.

5. The lamp is operating at the correct current (check ammeter calibration).

6. Do the "bullseye" alignment without the lens, adjusting the position and focus of the lamp (x-y-z position)

7. Tweek position and focus to obtain optimum uniformity of illumination with "open gate white light" projected on the screen (be careful not to overheat the lens) -- meeting standard SMPTE 196M:

quote:
5.3 Theater luminance limits
Theater screen luminance at the screen center shall be between 41 cd/m2 (12 fL) and 75 cd/m2 (22 fL).
Luminance at the screen sides shall be 75% to 90% of the screen center luminance, but not less than 34
cd/m2 (10 fL).

quote:
6 Luminance distribution
The screen luminance shall be symmetrically distributed about the geometric center of the screen. The luminance
of any point on the screen between the center and the edges, as measured from any seat in the middle row, shall
not exceed the screen center reading (see annex A.2). For screens with a gain factor of 1.1 or more, the screen
shall be curved for light uniformity as described in SMPTE RP 95. A more complete measurement of screen
luminance distribution is described in SMPTE RP 98 and is recommended for new or revised installations.

Remember, ALWAYS use the proper safety gear when handling xenon lamps, or that exploding lamp may be the last thing you ever see! [Eek!]

| IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1 2

Printer-friendly view of this topic

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.