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Topic: Lamp damage

Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 03-21-2001 06:29 PM

Hello everyone.

Today I've changed one of my mirrors in our Cinemeccanica V5.
I found, for the second time, that the lamp has a "spot" on the anode (is it the anode? the bigger part). It is a little piece of metal that is "growed" on the anode itself. On my previous lamp (Osram 2500W horizontal)a piece of metal "growed" on one side of the anode causing oscillation in the light beam. This time this "spot" is in the middle of the anod and all seems to be ok but I think that it is not normal.
Could be a rectifier problem? Should I have to replace all diodes?

I appreciate any suggestion you can offer!!

Thanks
Antonio

Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 03-21-2001 06:37 PM

If the spot is in the front middle where the energy crosses this is normal. To prevent this from getting worse like the previous bulb you need to rotate it a Quarter turn every 500 hours.

Does the cathode maintain its point or do you see cracks in it? This is the small one. The anode is the large one.

Paul G. Thompson
The Weenie Man

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

posted 03-22-2001 12:07 AM

I know this is a strange question, but does it look like a ding ball? ( I am not an expert on ding balls...) The Xenon bulb may be operating out of parameters. If not, the only anodes I have seen with a ball forming on the anode was caused, in part, by poor filtering of the AC ripple.

Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 03-22-2001 02:06 AM

Paul

Cracks in the cathode can develope off this too can't it?

Paul G. Thompson
The Weenie Man

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

posted 03-22-2001 12:15 PM

Darryl, I have seen the cathodes erode very badly, where the tip gets real blunt. But in all honesty, I have never seen one crack.

I have, however, heard that a re-design of the cathode may have happened, where the cathode was purposely manufactured with a split in it. Supposedly, the modification was made to increase the bulb life. Whether it was ever incorporated in ORC bulbs, I don't know.

Sorry, that is the best information I have.

John Pytlak
Film God

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

posted 03-22-2001 03:40 PM

As I recall, prematurely eroded electrodes and growth of metal deposits on the electrodes may indicate unacceptably high AC current ripple in the DC supplied to the lamp. One of the lamp manufacturers (Osram?) had a pictorial guide to different problems and their effect on lamp appearance.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000

posted 03-22-2001 07:22 PM

Antonio - is it a Zenith X-2000 lamphouse?

We had a similar problem with ours - overheating, progressively worsening anode pitting and then a flicker. In one case a lamp exploded as I was removing it for disposal after only 950 hours (it had been rotated at 500).

At first we believed that the intake fan wasn't pushing enough cold air in and added another one, but that didn't cure the problem. After much scratching of heads and quite by accident, one of my colleagues eventually found what was causing it. The DC shunts on the power supply to the lamphouse ammeters were of the wrong rating, resulting in the meters giving a false reading. The shunts in the lamphouse were 60mA, but the ammeter was rated at 75. So we were over-running the lamps without knowing it.

According to the parts catalogue, all Cinemeccanica meters and shunts are 60mA. But they're all imported from Italy, and equivalents are impossible to get from UK suppliers. 75mA appears to be the standard in Britain. I guess what happened was that the original meter failed at some stage, and was replaced by someone who did not know to check the shunt rating on the supply feeding it.

Anyway, ever since we replaced the shunt with a 75mA one to match the meter, we've had no problems with overheating lamps.

Gordon McLeod
Film God

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

posted 03-22-2001 08:56 PM

Also cinemecanica uses IREM rectifiers and there filtering and inrush current leaves much to be desired.

Randy Stankey
Film God

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

posted 03-22-2001 11:24 PM

Do you mean like THIS?

When this lamp was taken out it had 6500 hours on it! ...and people were wondering why the picture was dim!

Sometimes you'll see the surface of the anode get rough and "pimply". The cathode will get rounded off as well. Of course this is an extreme example but a CERTAIN amount of this is normal.

I'd say to check your current and change your tap settings if needed. Also check for ripple like other people have said.

Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 03-23-2001 08:28 AM

Randy,

ARGH! No, nothing like that!!! I have an old 3000 hours lamp (I'm a projectionist since only 2 years and I haven't saw others old lamps!) and it seems so better than yours!!!
No, my "spot" is nothing compared with your photo. I will shot an image of the lamp and i'll post here.
Leo: no, are Zenith X4000. However, since I'm in Italy, perhaps shunts should not be a problem here!!!
And, Gordon, Yes, we use IREM rectifier.

I will post a photo soon.

Thanks to everyone!
Antonio

Neil Fish
Film Handler

Posts: 16
From: Norwalk, Ct
Registered: Dec 2000

posted 03-23-2001 08:15 PM

Antonio- The symptom you describe sounds like a classic high inrush current problem. Have the filter capacitor tested. BTW- If this is an Osram bulb they will analyze it for you and give you a diagnosis of the likely problem. Also, as John mentioned, Osram does put out a book with photographs of various lamp maladies and their causes. I find it very helpful in diagnosing xenon system problems.

Stefan Scholz
Expert Film Handler

Posts: 223
From: Schoenberg, Germany
Registered: Sep 1999

posted 03-24-2001 04:38 AM

To answer Leo's shunt item,

Continental ammeter shunt value has been 60 mV (Constant Voltage) full scale for a long time since the 1910's. Later, with international standardisation, in the 90's, it tended to change to 1 mA full scale, giving 75 mV for 75 Amp meter, 35 mV for 150 Amp meter. With Italien projectors of different make, sometimes older meters and newer shunts (and vice versa) were mixed in transition, so the setup tech had to check the combination when delivering the projector. (As you know, they always had apologies for "bad quality", and promised to do better "next time".)
Even today theese 60 mV shunts are still available on request, as are the meters. Any new stuff in cataloges is 1 mA.

Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 03-24-2001 06:59 AM

Neil,

Where this book can be found?

Thanks
Antonio

Gordon McLeod
Film God

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

posted 03-24-2001 02:53 PM

Irem rectifiers (3 phase) typically have fairly small filter caps so inrush is usually not a big problem compared to the amount of ripple

John Walsh
Film God

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

posted 03-24-2001 03:33 PM

The book is: "XBO Theatre Lamps - Technology and applications" avaiable from Osram.

It would be a good book to include in the download page, but there are a few good quality B&W photos that might not scan/pdf well.

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