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This topic comprises 2 pages: 1 2
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Author
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Topic: Diode Failure on Christie
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Scott Hicks
Film Handler
Posts: 24
From: Portland, Oregon, USA
Registered: Mar 2000
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posted 03-13-2000 09:15 PM
Joshua,In almost every case, when the breaker blows, a diode has shorted in a non-switching rectifier. We advise changing all 4 or six diodes at the same time, from a future reliability standpoint, but if you can determine the defective one, replacing just that one diode will get you back on screen. Changing diodes is fairly easy, I've seen many a projection booth stocked with a couple spares. Of course, if you're close to a local tech, it's better to have an expert do the dirty deed.
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Zach Zagar
Film Handler
Posts: 45
From: Jefferson City, MO
Registered: Mar 2000
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posted 03-13-2000 09:30 PM
Hi, sorry, I'm new here, but I have worked on Christie's for about 3 years now (no, not a master, but can do some amount of tricky stuff). Anyways, yes, diodes aren't very hard on the Christie lamphouses. You could change one at a time if you have an OHMS meter, but its much quicker to change them all and not to mention, yes, keep it uniform, may as well change em all if you're in there.As for the rectifier being smaller, well, aside from the technical aspects pointed out earlier, there has also been some degree of miniaturization in EVERYTHING (not just projection booth), over the years, which could account for a change in the size. Ok, enough rambling from a newbie.
Zach
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 03-14-2000 10:32 PM
Joshua:I use CFS lamphouses @ TT-17. I've got LOTS of experience changing diodes. CFS lamphouses **EAT** diodes for lunch!!! After a while, you get pretty good. Honestly, it isn't really hard. For the CFS, I can name all the tools you need right off the top of my head: 1 - 9/16 socket wrench
1 - 7/16 mini-socket wrench
1 - 7/16 open end (dog bone) wrench
1 - flat/ regular size screwdriver
3 - 150K120A diodes (RCA / Mouser preferred)
3 - 150KR120A diodes
1 tube of heat-sink grease
some alcohol and a wiping cloth
an ohmmeter/DMM I don't say all that to show off. I say it to show that it isn't all that hard, once you learn. After the first 9,000,000 times we just say, "Oh Sh**!, Where's the tools?" We had this old broken-down make-up table that we stripped for replacemant parts so we turned it into a "Crash Cart". We just put all the tools and diodes, etc inside it and leave it in a "central location". On a good day we can fix a blown diode in 20 minutes or less!
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 03-15-2000 12:01 PM
We use RCA diodes, now from Mouser. Our chief Tech recommended this. He also told me what the ratings/markings mean but I don't think what he told me is right. I didn't want to argue with him so I just let it drop.Here's what I understand: 150K?120A = 150,000v Peak Inverse Voltage (PIV) and 120A max. forward current (I-max) if "?" = "R" then it's a reverse polarity diode. Our tech says it's the other way around. Since diodes are supposed to be rated 2.5 times the I-max, that means we should use 150k?150A at minimum. Which one of us is crazy??
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 03-15-2000 12:27 PM
Randy:A diode with a 150,000 volt rating would be quite an accomplishment!  The International Rectifier 150K100A rectifier has a forward current rating of 150 amperes at 150 degrees Celsius maximum, and a Vrrm of 1000 volts. So by inference, the 150K120A would have a maximum forward current of 150 amperes and a Vrrm of 1200 volts. If your rectifiers "eat" diodes, are you sure you have enought air flow over the heat sinks? I knew that BSEE degree would come in handy some day!  ------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 03-15-2000 03:01 PM
Okay, now I get it.Still, everybody I've talked to says that CFS are well known diode eaters. We had one of our guys take the schematics in to his tech school and his prof. said that this design shouldn't do that. Since we started buying better diodes it's happened a lot less but it still happens occasionally. There are blower fans down in the power supply that are SUPPOSED to keep the rectifiers cool. From my experience it has limited success. When the fans stop working, you've probably got a week or two to replace/fix it before diodes start blowing. (That happens a lot, too!) I guess the moral of the story is, "If you use CFS you'll have to change a lot of diodes!"
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Patrick S. Chaffins
Film Handler
Posts: 11
From: Mount Clemens, Michigan, USA
Registered: Feb 2000
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posted 03-15-2000 08:42 PM
Power supply cooling is VERY important!!!! Most power diodes will start to fail at about 80°C (176°F). (That number comes from looking at data sheets for the last five hours today) That's the case temperature, not the temperature of the heat sink! There is always some heat transfer loss between the diode and the heat sink. If it feels like the heat of a hair dryer coming from the P.S. exhaust then there is not enough air flow. Putting in higher rated (Current) diodes will help somewhat, however it generally just puts the replacement timing farther apart, (they will eventually fail). From my experience in working with high current power supplies in the last 30 years there has never been excessive heat sinking or airflow incorporated into the design. (Just put in enough aluminum and fan to keep it below the fail temperature of the device.)
Moral of this story:
1. Keep the openings clear
2. Keep the blowers cleaned and oiled
3. Keep the heat sinks clean (all them fuzzies rob the heat transfer severely)
4. Make sure the diodes are bolted securely (especially after moving the Power Supply and during installs)--------------- may your lights be bright,
your screens clean
your prints scratch free
and your sound warm and not fuzzy
Pat PS is there anyone else out there from the Detroit area?
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