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» Film-Tech Forum   » Operations   » Large Format Forum   » Lamp Flikering on a frequent interval

Author Topic: Lamp Flikering on a frequent interval
Peter John Anthony. C
Film Handler

Posts: 55
From: India
Registered: Jun 2004

 - posted 08-05-2007 06:31 PM      Profile for Peter John Anthony. C   Email Peter John Anthony. C   Send New Private Message       Edit/Delete Post 
For 15/70mm IMAX Projection we use Miller 812 rectifier to for lamp.
Now the problem i am facing is the light falling on the screen is not steady.
Every 3/4th of a sec there is a variation on the luminance that is the brightness goes up & after 3/4 sec it comes down. If measured the current flowing on the lamp is less by 80Amps when compared with the reading we use to get before when we get this problem.
The ripple current i am getting on stand-by mode is 28A & on full mode we are receiving 75A.. Could any one help me out to solve the problem please... Is the ripple Curent what I am receiving is normal ??

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Dan Reiter
Film Handler

Posts: 74
From: Easton PA
Registered: Jul 2002

 - posted 08-06-2007 09:09 AM      Profile for Dan Reiter   Email Dan Reiter   Send New Private Message       Edit/Delete Post 

A few questions for you, that maybe can point to a problem.

1. Is this "drop" rythmic, and happens constantly? If so, is the power supply making any noise, such as a relay or contactor clicking when the change occurs?

2. Do you have any added circuitry that drops the lamp's current level between shows that could be malfunctioning?

3. What is your on-screen lamp specs? (Current & voltage) vs your standby?

4. You have not mentioned the lamp. Is the arc (flame) steady, with no flicker or flame problems? What is the condition of the lamp, and hours on your current lamp?

My thinking is to focus on the power supply, as maybe you are having a diode problem where one is starting to fail and rythmicaly shorting, based on an overheating cycle. You seem to have excessive ripple and flicker, so that is guiding my thinking.

Is the power supply running hot, and it is cycling? Are you running over-current, and getting clipping? Have you had any alarms from the system? How are all lamp & DC connections? If there is a bad connection it will affect the lamp's operation as well.

The jumping current points to the power supply and a problem there. If the current did not change rythmically, and held at the same level, then the lamp would be the focus of attention.

Hope this helps..

Dan Reiter
Superior Quartz Products.

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Ben Wales
Jedi Master Film Handler

Posts: 602
From: Southampton. England
Registered: Jul 99

 - posted 08-06-2007 12:04 PM      Profile for Ben Wales   Email Ben Wales   Send New Private Message       Edit/Delete Post 
Peter: Is your Imax System 3D SR Projectors or MPX?.

I assume that you operate the smaller Imax System like the above with 7kw Xenon (Air Cooled) lamps.

Have you contacted your Imax Service Tech with the above problem?, I suspect as already posted it would a DC supply problem, but worth while to check the condition of the Lamp as well Air Flow on the Lamp and with the Miller Rectifier.

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Gordon McLeod
Film God

Posts: 9461
From: Toronto Ontario Canada
Registered: Jun 99

 - posted 08-12-2007 03:33 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
I suspect that you have a phase missing or a diode gone
Also the standby to full control may be faulty
On the older big 15k miller systems the rheostat for current adjustment could have a problem with the brush contact on it

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Troy Hilsman Powell
Film Handler

Posts: 30
From: Jacksonville,FL
Registered: May 2007

 - posted 08-14-2007 08:06 PM      Profile for Troy Hilsman Powell   Email Troy Hilsman Powell   Send New Private Message       Edit/Delete Post 
Check those caps in the power supply....Are they leaky?

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System Notices
Forum Watchdog / Soup Nazi

Posts: 215

Registered: Apr 2004

 - posted 09-11-2008 07:46 AM      Profile for System Notices         Edit/Delete Post 

It has been 393 days since the last post.

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Dan Reiter
Film Handler

Posts: 74
From: Easton PA
Registered: Jul 2002

 - posted 09-11-2008 07:46 AM      Profile for Dan Reiter   Email Dan Reiter   Send New Private Message       Edit/Delete Post 
Has there been any resolution of this?

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