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Author Topic: Replacing blown diodes on Christies Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 03-29-2006 03:41 PM                    We have had several experiences with a diode going out in the middle of a show. We replace it and think nothing more of it. We have been noticing that when one diode goes out, it is usually follwed by another one...and another one...all on the same projector, sometimes weeks apart, sometimes a month or so, sometimes never. It sounds like the one diode going out might be weakening the others in some occasions. My question is this: When one diode goes out, do you simply change that one diode and hope the others don't fail? Or do you anticipate the other diodes following suit and just change them all at the same time? It seems like a waste of "good" diodes, but then with the potential of the projector going out in the middle of another show...and the past track record of additional diodes going out soon after, it only seems logical to change them all and avoid future problems. Anyones input on this matter would be appreciated. Also, if anyone knows Christies official recommendation, I'd like to know that.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 03-29-2006 04:19 PM                        Older Christie's had "low p.i.v. ratings" and were prone to failure. Best to use at least 1000 volt p.i.v on them. There is no general agreement on your question. I usually replace only the bad one unless I am upgrading the p.i.v. Louis  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-29-2006 04:48 PM                     Replace the one that's bad just to get the show back on the screen as quickly as you can. If you've got an "Emergency Kit" all ready to go with the tools and spare parts you need to do the job it might only take you a few minutes if you work smartly. As soon as you have time, change all the rest of the diodes. If you don't you're bound to have them blow, one after another. Make sure you use enough heat sink compound. If you don't they will blow even faster. If you can, get diodes with a higher PIV. They'll last a lot longer. There is a kind of diode that's made with glass instead of epoxy inside to seal the parts together. I believe it's called "Glass Passivated". (Please correct me if I'm wrong, here.) They may be more expensive but you'll only ever have to replace them once.  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 03-29-2006 04:57 PM                     I used to be in the 'change only the bad one' camp, and this worked OK on the many older IREM supplies I delt with. But for some reason, with the newer supplies, I've had the same experience; one goes, then another, etc. So now I'm a 'change em' all' guy. I don't want to risk loosing a show. I think what happens is, when one shorts, the other diodes conduct "into" the shorted diode for only the time their phase is on, which weakens them. That's why they don't die right away. A suggestion might be; if you take out the bad diode and it's shorted, replace them all. If it's open, just change that one.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 03-29-2006 05:29 PM                        Also, there is a blower right underneath the diode heatsink of the Christie PS. In older machines, these are almost always out and that may be overlooked since you switch off the PS for diode testing and changing. But do check the blower, even though it is hard to see, with the PS switched on.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 03-29-2006 05:43 PM                        I'm with Louis on this one. I had an ORC supply that would blow diodes at least once per year... usually between shows (back when we shut the lamps down). Moving to a higher PIV required drilling the heat sinks out a bit, but I never lost a diode on that supply after that.  |  IP: Logged Mike Blakesley Film God Posts: 12767 From: Forsyth, Montana Registered: Jun 99 posted 03-29-2006 06:16 PM                        quote: Randy Stankey As soon as you have time, change all the rest of the diodes. If you don't you're bound to have them blow, one after another. You must have stock in a diode manufacturer! Our Christie tends to blow a diode every couple of years, if that. I have always just changed the blown one. Following those instructions I'd've spent over 2000 bucks replacing perfectly good diodes by now. I think this is a classic case of "your mileage may vary."  |  IP: Logged Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 03-29-2006 07:21 PM                    we do have a kit ready ready to go, but I guess I dont know how to work "smartly". It seems that when a diode blows, its a crap shoot as to which one is blown. We do keep track of blown diodes, but i'm curious if there is a "smart" way to proceed when it comes to replacing them. Are there signs to look for? I'd love to save time replacing these things.. Thanks!  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 03-29-2006 10:20 PM                     I haven't had a diode fail since 1992 when I was working with CFS lamphouses. I would tell you my secret, but then it wouldn't be a secret now would it? I'm in the "change them all and upgrade them while you're at it" camp.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-29-2006 11:13 PM                     I don't keep any secrets.... they are all divulged here on F-T!Always replace all of the diodes and only use Semikron diodes. They have a rating of 1600 volts 140 amps in the same size package that a normal 85 amp diode fits in. I never have had one fail and they are an inexpensive part available from Allied Electronics either with leads for Irem, or without leads for Christie, CFS, Strong. Big Sky and Newmaid charge over 30.00 apiece for these Mark  |  IP: Logged Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 03-30-2006 12:33 AM                    Well the exact replacment diode to get also confused me. The manual lists 3. I assumed they were different diodes for different power supplies. Our 4000 watt lamp houses use different diodes than our 3000 watt house.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 03-30-2006 03:35 AM                        quote: Brad Miller I haven't had a diode fail since 1992 when I was working with CFS lamphouses. What, cut an opening and mount a blower to ventilate the power supply better in that ridiculously small compartment? That's what we did and it seems to have helped. We used to have diodes out in our CFS consoles regularly, but not anymore since.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 03-30-2006 04:55 AM                     It's much easier to just not work with CFS lamphouses. Seriously though, heatsink, damned tight connections and higher rated diodes (when/if the initial set fails) is all I do. To date I have never had a Christie SLC diode fail on me, but upgrading the diodes has worked wonders for me in Strong and other rectifiers.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-30-2006 06:26 AM                     Actually cfs power supplies are/were made by LP assocciates and they are not that bad.... many are just very old. They are in fact the only good part of the console. As Michael said a fan also works wonders... Replace the rest of the cf guts with a christie plenum kit. A bit of work but worth the effort. The high reactance rectifiers Strong supplies today are LP rectifiers!!  |  IP: Logged Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 03-30-2006 10:23 AM                    Well, would anyone have a part number on a REALLY good set of diodes? I am personally getting sick of replacing these. All our brisge fans work fine and are cleaned out regularly. We have just been ordering the replacment diode that the book calls for, but if theres a better part available, please let me know where we can order it and maybe a part number for neg/pos diodes for a SLC30. Thanks!!  |  IP: Logged

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