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Author Topic: Can you check a diode without removing it? Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 07-13-2006 03:52 PM                    I was just curious if it was possible to get any kind of reliable reading while checking diodes without actually taking them out first? We have a Christie P35GP with 6 diodes. When these things go out, 99% of the time taken to replace the bad diode is used removing perfectly good diodes to check them, then replacing them and moving on to the next one. I am not aware of a proceedure to get an accurate reading without removing the diode first, but was wondering if anyone else did? We'd really love to be able to find the bad diode and replace it, and get the show going again. A blown diode usually means a blown show and passes, but a quick repair would not only make customers happy, but save us a lot of work. Thanks  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 07-13-2006 05:57 PM                     Yes, as long as you completely disconnect one (or both, in some cases) ends of the diode from the circuit, and leave them bolted into the heat sink. -Aaron  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-13-2006 07:59 PM                        You can't accurately measure it without disconnecting one end, as Mr Sisemore pointed out, but one way to speed up the process to find the bad diode is to use a contactless laser thermometer and/or a current clamp. If a diode is shorted, it will get much hotter than the other diode as it conducts way more current. Although that often trips the breaker quickly, so there isn't much time for it to heat up. But you can often see the difference in temperature. An open diode will be colder. Or you can check the cables going from the mainboard into the diode heatsink with a clamp-on ampmeter. It will quickly tell you which diode is conducting excessive, which is conducting no current.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-13-2006 08:25 PM                     Oh come on guys... If you're doing your job corectly you will simply replace all of the diodes and you will be both time and money ahead of any repeat failures of the others you didn't replace. Even a semi-experienced tech can replace them all in about 30 minutes. Repeat failures of the ones you left in there usually happens shortly down the road or at the next power bump. Diodes have a finite life and they tend to mechanically break down from the repeated thermal expansion and contraction they constantly undergo. An entire set of diodes is alot cheaper than refunding a house with just 30 people in it. Also get the latest diodes. The IR diodes that Christie uses are not all that great. I use Semikron diodes rated at nearly double the current of the Christie diodes and they are in the same size case. They are much less expensive once you know where to get them and far more reliable than the IR originals that came in your rectifier. Mark  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 07-13-2006 08:57 PM                        Good point Mark. It's kind of like a fouled spark plug in a car. You don't just replace the one beause you know the others aren't 100% even if they haven't yet failed, and its not that much more work, and its cheap enough simply to avoid another breakdown in another few weeks. At the Wynnsong, ours sat in a block (pack), you can't remove them one at a time. You pull the whole block. And one of the few things we did right there is we had a spare block. Remove the old, put in the new, and you're back running. Then you take the old block to your service bench and do the replacing there taking your time to do it right, because the projector's running with the new pack. If you still feel the need to do testing and replace just the bad ones, you'd do it then, since you have time. I'd say replacing just the bad one is only for an emergency situation (sold out premere of Star Wars Ep. 7: the return of Darth Plattrus), and only if you can tell by sight (scorched), because it probably won't save you any time, and may cost you more.  |  IP: Logged Christopher Seo Jedi Master Film Handler Posts: 530 From: Los Angeles, CA Registered: Jun 99 posted 07-13-2006 09:59 PM                     If one has a desire to get electrocuted, couldn't one read the voltage drop across the diodes while the rectifier is on?  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 07-13-2006 10:19 PM                        Standard voltage drop is either .7 or .3 V. Projector diodes I'm not sure about. But if you're getting a very high drop, would indicate an open circuit, and a low to nonexistant drop would indicate an internal short. But I wouldn't be messing with anything that powerful hot. Best just cut power and remove the whole pack and replace. Besides, even if you found the bad one without electrocuting yourself, then what? You'd still have to power down, remove the diode, or pack, and replace. Might as well just do them all while you're in there.  |  IP: Logged Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 07-13-2006 10:31 PM                    I agree with replacing them all, but my goal is to get a bad diode changed out as soon as possible to get the show going. Even if we have to hand out passes...at least the customers didnt have to wait for the show to continue. I dont know how comfortable I am poking around inside there with the power on...I might have to continue doing it the slow way.  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 07-13-2006 10:49 PM                        Yeah, better safe than dead I always say.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-13-2006 10:49 PM                     Frank, I think you missed the point completely. You can change them all out faster than you can find the bad one. It still involves disconnecting one end of each diode anyway and with the correct tools its a breeze. Have a tube of GC Silicone heatsink grease at hand when you do it. Absolutely DO NOT work on a live rectifier. Even the expereinced have been electrocuted this way. Some rectifiers are pretty tight with a lack of space inside and sharp corners and metal edges... and worst of all... the recoil that you will endure from contacting live AC can and will do more damage to you than contacting the voltage itself. Literally.... people have been thrown far distances. Respect any voltage source and you'll be fine. Also, make it mandatory that someone in your theater know CPR and that they are aware that you are working on AC/DC equipment. Above all SAFETY FIRST around ANY electricity! And check Out These Cool Electrocution Photos! And I used to work around an 18kv 20 amp source! Mark  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 07-13-2006 11:03 PM                        Mark, I love it. Blah blah blah, safety first. And I agree with you, but I love the wrap up, it like "Oh by the way, check out these really cool electrocution pics" Smooth.  |  IP: Logged Frank Dubrois Jedi Master Film Handler Posts: 896 From: Cleveland, OH Registered: Mar 2005 posted 07-14-2006 12:03 AM                    Mark, you said that you can also get better diodes fairly cheap. I think we spend about $30-$35 for the crap christie diodes. What are the "good" ones going for? and whats the source?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-14-2006 03:24 AM                     You know Mark I only replace the bad diode and most of those rectifiers spend another 10 years before they have an issue the one exception is the allinson rectifiers as they are matched sets  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 07-14-2006 07:06 AM                        DAMN that Photoshop! Yah, very cool pics, but fortunately for the guy on the pole, there's a 90% chance this is just very pretty doctoring. How to tell? Check out his partner in the lift (with the hard hat). What to you think the chances are that he would still be in the same postion in picture 3 that he is in picture 1? His buddy explodes above him and after all those spectacular fireworks, he is still reading or whatever he is doing in picture 1. VERY suspect. On the other hand, it sure does make for a dramatic reminder when playing around electricity. BTW, even before you insist that someone in close proximity know CPR, never ever work around electricity alone, especially after hours like many of us do after the theatre closes.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-14-2006 07:48 AM                     quote: Frank Dubrois I think we spend about $30-$35 for the crap christie diodes. Clearly Frank... if this is for a diode in a 2kw unit you are getting ripped off...! We might charge that for cetain 4K diodes but I don't think so. No, I won't divulge where we get the Semikron diodes from and we do get them in quantity.... You have to learn to do some of that figuring out on your own. There is a google and an internet out there to utulize. Even the IR diodes can be bought for very little $$ each but they are almost the same price as the higher rated Semikron is.. quote: Frank Angel What to you think the chances are that he would still be in the same postion in picture 3 that he is in picture 1? Frank, Note that the guy in the bucket's head is above the roof line in photo # 1, at the roof line in #2, and below the roof line in photo #3. Also note the flexing wire the guy is getting fed the 16kv from being in different positions. I bet that whole thing lasted less than 3 seconds and while the bucket guy was on his way down. Power companies train their guys to look in the direction they are headed in those lifts for good safety reasons. Most Nikon or Canon motor driven cameras are capable of 6 fps. Gord, Humm, I know a guy in Kinmount that needed diodes replaced sooner than 10 years. But what the heck... there is nothing wrong with getting in an extra service call or two.... Mark  |  IP: Logged

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