Film-Tech Forum ARCHIVE: Christie rectifier problem.

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Posted by John Spooner (Member # 1565) on 05-04-2003, 02:57 PM:

Dear colleagues. At one of our theatres we have 2 Christie rect. units of 3.5 kw rating. They are about 10-15 years old.
About 55 mins into the first spool the xenon went out and would not restrike (hv striker cct operating ok and correct spark in lamp). There was the characteristic smell of transformer wax also and no dc voltage to the lamp.
With the lamp off, I took ac current readings of each phase and noted one phase was drawing 16 amps at no load! (the supply voltage in Oz is 240vac).
After about 20mins the dc voltage returned and lamp was able to strike, also all phases levelled out and were balanced again.
We have 2 machines and were able to run remainder of show on the other one (an advantage of the 2 machine system).
Has anyone had a similar experience with the Christie unit or could advise remedial action. I understand these units were very basic and had diode problems, we are of the impression that there is a diode failure and subsequent short to ground.
Regards. John S.

Posted by Jon Bartow (Member # 241) on 05-04-2003, 04:44 PM:

If, when the unit is turned off, you are drawing 16 amps off of one phase then you have a serious problem. I would highly advise that you not use that unit until it has been repaired. It poses a fire hazard.

Is the contactor closed when you are reading the 16 amps?

My gut tells me that you've had a transformer melt down. Did this unit "buzz" a lot when it was on?

I've had two 3k Christie rectifiers of about the same vintage catch fire in the last year in one of my theaters. They buzzed really bad before burning up (I do mean actual flames. A weenie roast for Paul [Big Grin]

)

Posted by Paul G. Thompson (Member # 655) on 05-04-2003, 04:49 PM:

I concur with John. I also recommend the tap selector unit (if the power supply is equipped with that) be carefully inspected. Those switches were very troublesome in the early units.

Posted by Mark Gulbrandsen (Member # 72) on 05-04-2003, 05:22 PM:

This one is easy. What you have is a diode that has gone bad mechanically....meaning that when it gets hot it fails, and when it cools down it goes back to normal state. You will probably find the stem on this diode physically loose, or it may break off when you go to remove it!! This is not at all uncommon on Christie and other rectifiers. If you have diodes that have the greenish epoxy filler in them then REPLACE THEM ALL. In fact on a rectifier this old I would automatically just replace them anyway as you WILL continue to experience this type of failure of them. Try to find glass passiveted diodes if at all possible...they are far more reliable then the cheap epoxy passivated type that Christie(and others) are still using. This mechanical or structural failure of the diode is also very common in old ORC 1000 lamphouses and in the 68000 series high reactance units from Strong.
This is also the reason that many Christie rectifiers experieince transformer failure and catch fire. Some failures will actually continue to run and the main breaker will not trip since it is a low current short....but not low enough to not keep the windings on one phase fomr getting hot enough to catch fire after a prolonged situation like this. On the 2.5kw and larger Christie units we automatically retrofit them with the diodes and fibrglas insulator strips from the 4kw units and never ever experience any failures after that. Theatres in places with poor power regulation are also urged to do this mod.
Mark @ CLACO

Posted by Phil Hill (Member # 371) on 05-04-2003, 05:39 PM:

I agree Mark....it's the diodes.

Also, I am very surprised and disturbed to hear about the UNACCEPTABLE design and poor engineering by Christie that would allow something to physically catch on fire! I wonder if the UL people are aware of this? This seems like a very dangerous and possibly expensive liability for Christie.

>>> Phil

Posted by Steve Guttag (Member # 268) on 05-04-2003, 06:01 PM:

I use a lot of Christie rectifiers and have never had one catch fire...the only inordinate amount of diode failures were in installations where new contruction was going on and voltage spikes took out the diodes....installing surge supression nixed the diode failures too.

Mark, Christie is going to 150A diodes across the board in the future too..away from the DO-5 package as used on typical 3KW and smaller rectifiers.

Steve

Posted by Stan Gunn (Member # 554) on 05-05-2003, 03:49 AM:

Hi John

Yes a diode is a possable cause on one phase, butI would have thought that a circuit breaker would have let go.

Send me the model of the supply, I should have a circuit for the 415 three phase Aust version.

I have seen many around, I think they are a good rect,
usally just sit there in the corner and work.

Some had a temp sensor on the main tranny. [Razz]

Posted by Mark Gulbrandsen (Member # 72) on 05-05-2003, 08:54 AM:

Also, check to see if some dumb electrician installed too large of a breaker for your rectifier!!! I forgot this before...have seen this done several times.
Mark

Posted by John Spooner (Member # 1565) on 05-05-2003, 11:11 AM:

Dear colleagues. Thank you sincerely for advice to date.
Jon, the contactor was energised to enable the current test, good thing I left my tong tester there. Current in other 2 legs seemed normal and ok. The red phase windings were very hot, much hotter than the other 2 sets.
Mark, I checked the diodes and the pin was loose on one of the diodes and turned around easily as you stated, so hopefully it was mechanical failure as you state, also when it cooled the lamp came back on. I was personally amazed at the small diodes used for a large current, they will be replaced with larger ones as soon as practicable.
Stan, have sent you a personal note re the book and specs.
Thank you again for info. My next screening at this particular theatre will be Thursday, so hopefully I can post some good results acting on info received.
John S.

Posted by Randy Stankey (Member # 64) on 05-05-2003, 09:44 PM:

Christie rectifiers do catch fire!

Not 100% sure of the cause because I was only there for the aftermath but not for the actual festivities. Nearest we can tell is that some doofus tried to change the diodes and did a piss-poor job. We're not sure that was the real cause because when I got there all the diodes had been completely removed. I think the guy was trying to cover his tracks.

The guy didn't get canned for what we did but this certainly got filed away in the memory banks. They finally got him for a whole bunch of things all rolled up into one, this incident being just ONE of the charges.

Posted by Pete Naples (Member # 761) on 05-06-2003, 02:13 AM:

I've had one do exactly the same as the picture above! Two diodes failed short at the same instant, and.....

Posted by John Spooner (Member # 1565) on 05-06-2003, 12:17 PM:

Dear colleagues, I am pleased to advise that our Adelaide repairman from Atlab called around and fixed the unit. It was actually 2 diodes that had failed, so a repeat performance of Peter`s experience.
Randy, you must come across some clowns in the course of your business, the rectifier incident was an example of cover-up and the business of the "little Sh-t" lying to you regards the framing knob and other matters in a previous post shows total lack of professional ethics on their behalf.
Once again, thank you to date to everyone for your interest and advice in this matter. John S.

Posted by Randy Stankey (Member # 64) on 05-06-2003, 01:10 PM:

Not to go too far off topic, (as if this would be the first time), but I did have one or two theaters where the people working there were good.

I'll go so far as to actually name a good theater in my area:
Cinemark Movies 10 on Candler's Mountain Road in Lynchburg, VA.

The "guys" who ran that place were probably the best in my region.
Their machines were always kept clean. Film never got scratched. I almost never heard from them. Maybe, once in a while, they would send me an e-mail and ask me for advice on a problem or to order them a part that they didn't have authorization to order for themselves. If I got a phone call call from them I KNEW there was a major problem problem!

I'd visit there once every couple of months to give them their preventative maintainence and I'd never see or hear from them until the next time! I wish more of my locations were like them!

Posted by Michael Schaffer (Member # 1204) on 05-06-2003, 01:25 PM:

How can you fail to install diodes properly? It is not so difficult. Why are people who can`t do that properly allowed to mess around with electrical equipment?

Posted by Randy Stankey (Member # 64) on 05-06-2003, 03:22 PM:

They open up console and remove all the diodes. Then they put the new ones all in a big pile. A diode is pulled out of the pile and installed in a haphazard manner. The process is repeated 5 more times.

I had caught "somebody" doing the same thing before. Usually when this "happened" in the past the breaker on the console would trip. Then I would get a call to come fix it.

For some reason, this time, all hell broke loose. Maybe the projector had enough abuse and finally kicked the bucket? Maybe the guy fucked it up worse than usual? I don't know. All I know is that the phone rang and the guy on the other end told me that the projector was on fire.

The guy wanted to use a fire extinguisher on the thing. I had to yell at him NOT to do that. (If he had, the damage would have been 100 times worse!) I just told him to shut off all the power to the console from the breakers on the wall and just let it burn out. They were given instructions to pull the fire alarm and evacuate the building if it didn't go out by itself.

When I walked in there, there were tools all over the floor and all the diodes were out. When I got there, I just took one look and said, "Oh, shit!"

Posted by John Pytlak (Member # 331) on 05-06-2003, 04:08 PM:

At the drive-in, we had a CO2 fire extinguisher for minor electrical fires -- pretty effective, but without causing further damage to the equipment or risking shock.

Posted by Jon Bartow (Member # 241) on 05-06-2003, 08:31 PM:

Randy,
I had a Christie 7K SLC console (SLC-45?) that had very similar damage. What happened was the Capacitor (big, big cap for that 7K unit) shorted. It melted the nicrome wire, burnt a buch of wiring (actual flames, damage very much like yours), and blew oil from the cap all over the inside of the console. It took me three hours just to clean the thing. Then I had to use four spare caps from 3K units (and two of the 3k's nicrome wires) to get the thing running again until the proper cap could be procured.
Jonathan