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Author Topic: Replacing rectifier diodes Michael Pace Film Handler Posts: 64 From: Dalby, Queensland, Australia Registered: Aug 2000 posted 03-15-2001 08:15 AM                     I had to replace a diode this morning in the rectifier in the base of a CFS console. I only replaced the shorted diode and this enabled me to get the session up and running with a minimum of delay. The question is this - is it better to replace all the diodes in the negative bank (every diode I have replaced has always been in the negative side) or is it sufficient to only replace the defective diode. What are your thoughts on this? Michael. Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-15-2001 09:56 AM                     Michael, The correct thing to do is to replace all of the diodes in the negative and positive sides, especially if they are the epoxy sealed type. One of the problems that allot of techs overlook is that of the diodes reaching their limit on thermal cycling. If you replace the single diode the others will eventually keep on failing! The junction inside a diode gets quite hot and can only expand and contract so many times before it lets go. Usually the manufacturer publishes this spec in their data. This type of diode is really crap and if you have this style you should dump them and get the glass sealed type. After many thermal cycles the epoxy filled type can actually become mechanically defective and the stem will loosen up. This typically does not happen with glass sealed diodes. Unfortunately too many companies installed epoxy sealed diodes in their equipment, probably so their parts departments would fourish. Christie for instance uses them in rectifiers below 3kw rating and I have seen them in IREM's too. Mark @ GTS Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 03-15-2001 10:00 AM                    The only time I have replaced all of the diodes is when the size of the diode changed. We started purchasing a different type of diode and sometimes you may encounter some old ones so I just change them all. Changing just the bad one should be no problem. Note if you are still using the color sleaves around the diodes get rid of them. All they do is build up heat around the diodes causing them to fail faster. Another thing to avoid is constantly changing the tap settings. This can stress the diodes and cause them to fail. It can also screw up the fine tune tap adjustment that looks like a wire hanger by causing the weld to break on the middle leg. Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-15-2001 11:34 AM                     I agree that all the diodes should be changed but I also think that getting the show back on screen ASAP is important. Why not compromise? Change only the bad diode(s) now but go back and do a "proper" diode change at the end of the day. Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-15-2001 11:53 AM                     I completely agree with Randy on this. The show comes first and the remaining maintainance comes later. Replacing all diodes is the best route, especially if the piece of equipment has been in service for 5 or more years. The cost of new diodes is miniscule compared to the loss of income and customer fustration when the show doesn't run. Mark @ GTS Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 03-15-2001 01:40 PM                     Replace them all asap. Stephen Jones Master Film Handler Posts: 314 From: Geelong Victoria Australia Registered: Jun 99 posted 03-15-2001 08:24 PM                     Yep I tend to agree replace them all as soon as you can as I have been down that road of replaceing only the defective one.A week later the others started to go, so It's best to change the lot saves time and the risk of loseing a session for the sake of a few cents. Stephen ------------------

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