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» Film-Tech Forum   » Operations   » Large Format Forum   » IMAX Booth & Techs - Erratic reading of digital display on Miller Power supply

   
Author Topic: IMAX Booth & Techs - Erratic reading of digital display on Miller Power supply
Dan Reiter
Film Handler

Posts: 74
From: Easton PA
Registered: Jul 2002


 - posted 03-17-2010 02:39 PM      Profile for Dan Reiter   Email Dan Reiter   Send New Private Message       Edit/Delete Post 
I'm trying to solve a possible control board problem on a modified Miller 812. The voltage is reading high by about 5 volts during operation. It reads high on both the display and hand-held nmeter at the lamp.

Done all the usual connection checks, cleaned all connections, etc.

Is there a calibration procedure I can follow to test the internal electronics? Or, a good pointer for the problem?

Manhy Thanks!

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Tony Bandiera Jr
Film God

Posts: 2943
From: Moreland Idaho
Registered: Apr 2004


 - posted 03-17-2010 09:06 PM      Profile for Tony Bandiera Jr   Email Tony Bandiera Jr   Send New Private Message       Edit/Delete Post 
Shooting from the hip here Dan, as I have no direct experience with that equipment, but first off is the current within specs? How old is the bulb?

My understanding of Xenons is they are a constant current arc, and the voltage will rise as the bulb ages and the arc gap lengthens.

I'd try a different bulb if possible and see if things go back to normal.

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Gordon McLeod
Film God

Posts: 9443
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 03-17-2010 09:12 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Tony is correct in that as a bulb ages the current will need more voltage to maintain at the same level
Also the design of the rectifier also varries a bit especially on the amount of reactance in the output stage
Also how far is the rectifier away from the lamphouse

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Dan Reiter
Film Handler

Posts: 74
From: Easton PA
Registered: Jul 2002


 - posted 03-18-2010 02:37 PM      Profile for Dan Reiter   Email Dan Reiter   Send New Private Message       Edit/Delete Post 
We have two test chambers, and the bulb runs fine in the other chamber. So, that eliminates the bulb. As well, section by section, been either bypassing or disconnecting the IMAX modifications, no changes.

Still scratching my head on this one. [Confused]

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Rick Raskin
Phenomenal Film Handler

Posts: 1085
From: Manassas Virginia
Registered: Jan 2003


 - posted 03-19-2010 03:44 PM      Profile for Rick Raskin   Email Rick Raskin   Send New Private Message       Edit/Delete Post 
I also have no experience with this equipment, but from a purely theoretical perspective:

quote: Gordon McLeod
Also how far is the rectifier away from the lamphouse
Is this a new problem, in that it was operating fine before?

Is your operating current within spec?

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Tony Bandiera Jr
Film God

Posts: 2943
From: Moreland Idaho
Registered: Apr 2004


 - posted 03-31-2010 12:13 AM      Profile for Tony Bandiera Jr   Email Tony Bandiera Jr   Send New Private Message       Edit/Delete Post 
quote: Dan Reiter
...and the bulb runs fine in the other chamber.
So does the affected rectifier read properly when connected to the other chamber? If it does, then there is a loose connection somewhere associated with the first chamber.

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Dan Reiter
Film Handler

Posts: 74
From: Easton PA
Registered: Jul 2002


 - posted 03-31-2010 07:08 AM      Profile for Dan Reiter   Email Dan Reiter   Send New Private Message       Edit/Delete Post 
We can't swap these power supplies, due to the size, wiring, and complexity.

But, it runs fine for months, acts up, then returns to normal.

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Tony Bandiera Jr
Film God

Posts: 2943
From: Moreland Idaho
Registered: Apr 2004


 - posted 03-31-2010 08:41 PM      Profile for Tony Bandiera Jr   Email Tony Bandiera Jr   Send New Private Message       Edit/Delete Post 
Well if you can't swap the supplies then you may be stuck waiting for something to burn up or fail completely to find out what the cause is.

If you want to get to the root cause of this you're gonna have to take the time to swap the supplies.

What is so complex about the hookup that makes it we can't swap the units? I am aware that they're big, but what in world would be so difficult about swapping them out?

If unscheduled downtime would be a big problem, then I suggest you take some scheduled downtime to get this resolved. [Big Grin]

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Rick Raskin
Phenomenal Film Handler

Posts: 1085
From: Manassas Virginia
Registered: Jan 2003


 - posted 04-01-2010 07:39 AM      Profile for Rick Raskin   Email Rick Raskin   Send New Private Message       Edit/Delete Post 
I agree with Tony. The best way to get a handle on this problem is to split the trouble. Its either in the direction of rectifier or the load.
If it proves to be towards rectifier you should consider having the power company place a voltage graphing recorder on the line side. This may sound wacky but I once found an over-voltage problem caused by a faulty neutral connection.

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Gordon McLeod
Film God

Posts: 9443
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 04-01-2010 02:47 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
I have often noted difference in the voltage compared to amps with the miller conversion it was normal in many cases often the rheostat for current control contributes to it being eratic

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