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This topic comprises 4 pages: 1 2 3 4
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Author
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Topic: Rectifier Diodes
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Will Kutler
Phenomenal Film Handler
Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001
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posted 08-03-2002 04:32 PM
Diodes....Something that no one has mentioned. lamphouses and rectifiers also have many filter caps. If these caps go, rf signals can go back through the system and also cause havoc on diodes! I recently serviced a Strong Super Lume-X and High Reactance Power Supply. Many of the filter caps in the lamphouse were bad and played havoc on diodes in the power supply. (the guys at Strong helped me troubleshoot). They also suggested that I put some filter caps across diodes as extra protection, and these filter caps are not oem, but an after market Strong suggestion. Soldering diodes can be very tricky, and much care must be used. If you are not an experienced solderer, then stay away! Solder heat will ruin diodes! A generous amount of flux (to be cleaned off afterwords) and a hot, well tinned iron with a excellent tip and heat sinks (generally aligator clips) and proper mechanical connection prior to soldering) is a must! Also note that many diodes are installed with solderless connectors! Diodes can sometimes also be defective from the manufacturer. Ohms scale on a good multi-meter...I personally like analog over digital! can be used to check diodes. Caps need to be checked on a cap tester w/the proper value range!
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Paul G. Thompson
The Weenie Man
Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000
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posted 08-03-2002 05:30 PM
Will, are you referring to the RF suppression capacitors? There are usually several of those in the lamphouses, too. If the power supply diodes seem to fail faster than usual, I would recommend changing those RF suppression capacitors, both in the lamphouse and power supply as well. As we all know, the RF pulse from the igniter will really raise hell with the diodes if it gets on the DC rail.As far as changing the rectifier diodes, I still change them in sets. Diodes are cheap, and it is very cheap insurance rather than to risk a loss of a show, which usaually happens in a "Full House - Friday Night" situation. Some Xenon Power supplies (The heavy duty ORC's and some light duty Xetrons) use selenium diodes for the boost circut rectification. Seleniums have such a high internal capacitance that the RF pulse does not bother them too much. So those seldom fail. When they do, they'll really stink up the booth. I do not recommend replacing them with Silicone diodes. I tried that once in a 900 watt IREM, and it simply just did not work for very long. I hung a bunch of suppression capacitors across the diode, and it didn't do the job. I finally broke down and replaced it with an orginal style Selenium rectifier.
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Manny Knowles
"What are these things and WHY are they BLUE???"
Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002
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posted 08-04-2002 11:50 PM
It's interesting that this topic came up because I just had to fly out to another island to change diodes. I don't usually deal with the electrical components, so I sought out instructions from the technician in Miami.A simple test for continuity in both directions through the diode revealed the culprits (two were bad). I did not have a full complement of diodes, so I wasn't able to change them all. I just ordered a bunch, so that won't be an issue for a while. I was instructed not to use any chemicals on the heat sink, so I used a guitar pick* to remove the old and also to apply a layer to the face of the new ones. I was also advised to ascertain a tight connection. (I guess that's why each diode came with a replacement nut and star washer?) ~Manny (The director's cut). *The guitar picks made it into my tool kit after Bobby Henderson mentioned it elsewhere for cleaning buildup from the film bands in dirty gates. They have come in handy.
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Antonio Marcheselli
Phenomenal Film Handler
Posts: 1260
From: Florence, Italy
Registered: Mar 2000
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posted 08-08-2002 03:29 PM
Steve,perhaps IR has changed their codes... I found 87 HFR 120 and I became crazy to understand what that "7" means. I search the entire IR site and finally, at the end of a PDF datasheet, I found this: 85=Standard Device
86=Not isolated lead
87=Isolated lead with silicone sleeve (Red for reverse polarity, Blue for Normal polarity)
88=Type for rotating application I can send the pdf if you want! Bye
Antonio
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 08-09-2002 09:34 AM
Rick: What is the typical capacitor failure mode as they age (e.g., short, open, loses capacity, leakage)? Would there be some way of checking the capacitors by charging them to a known voltage, then looking at the R/C characteristic as they discharged through a known load? What is the typical value used, and is it different for different types of rectifiers (e.g., full wave bridge, 3-phase full wave) or lamp types?------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
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