This is topic Irem Rectifier Diodes blown up twice in one month! in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Demetris Thoupis (Member # 833) on 05-27-2001, 07:22 PM:
Hello all,
Well, I have this small problem with a cinema I am doing the projectors maintenance work and I was wondering whether you can help me. An Irem rectifier has blown two diodes twice this month and I am not sure where is the problem. All the diodes and connections are completely screwed very very tight so there will be no loose screws. What do you think the cause is? We all know that you have 16 screws to unscrew to reach to the diodes area and that is time consuming. Do you think the power is unstable? Suggestions please.
Thank you all
Demetris Thoupis"FOR STRENGTH AND HONOUR"
P.S: Irem Rectifier 3 phase - Country uses 240v power.
Posted by Aaron Sisemore (Member # 145) on 05-27-2001, 10:48 PM:
Did you use heat sink grease when replacing the diodes the first time? Without it many diodes won't last very long.
Power surges can also kill diodes, but heat is the biggest killer.
Aaron
Posted by Paul G. Thompson (Member # 655) on 05-27-2001, 10:55 PM:
Also check your RF suppression capacitors. Better yet, replace them.
Posted by Mark Gulbrandsen (Member # 72) on 05-27-2001, 11:29 PM:
Antonio,
I have had this exact same problem before with Irem rectifiers. You need to replace all of the diodes at the same time. There are not that many of them so it does not cost that much. A different date code batch of diodes can have slightly different charasterics even though they have the same industry part number an this can cause the thing to go slightly out of balance and put more stress on one or two other diodes. Always use silicon grease, and if in doubt replace the bypass caps. When I have them go I always replace all of them and the problem usually does not come back again.
Mark @ GTS
Posted by Brad Miller (Member # 2) on 05-28-2001, 12:49 AM:
I agree with Mark. I have had the same findings as he has expressed above. Always change them ALL out. 
Posted by Antonio Marcheselli (Member # 373) on 05-28-2001, 11:10 AM:
Mark,At the other cinema they have and have had many problems with their Irem rectifier, but this time it is not me to claim about my rectifiers!!! 
Bye
Antonio
Posted by Gordon McLeod (Member # 33) on 05-28-2001, 12:17 PM:
Also it is a good idea to use larger sized diodes in both PIV and amperage ratings. IREM uses the bare minimum to get buy
In most of the 2K Irems I service I have replaced the 35amp 200PIV diodes to 75amp 400PIV They cost about $2.00 more and don't fail as often
Posted by Steve Guttag (Member # 268) on 05-28-2001, 12:25 PM:
I agree with Gord...IREM uses too small diodes...I go a bit more overboard though and go with 800 or greater PIV and 85A.Are your diodes going bad during the show or when it starts? If it is during the show, then there is a possible heat problem...if it is at the show start then often it is RF coming back and killing them.
Make sure your lamphouse is grounded well...check your RF supression caps in and about the igniter they should be well connected to ground.
Steve
------------------
"Old projectionists never die, they just changeover!"
Posted by Paul G. Thompson (Member # 655) on 05-28-2001, 03:15 PM:
I have used 100 Amp 1000 Volt Peak Inverse diodes in all my power supplies. Failures were very rare. One thing you have to be very careful of all the stud diodes - you must use a heat sink when you solder the lead to them. If you don't, you can expect failures.
And, yes, be sure to use an approved heat-sink compound when they are installed. This also includes removal of all the coagulated compound from the mounting surface before you apply the new compound.
Posted by Gordon McLeod (Member # 33) on 05-28-2001, 09:32 PM:
I believe that the 100amp have a different stud size than the IREM uses
I believe that the 1/4" is maxed at 85amp but I could be wrong
Posted by Mark Gulbrandsen (Member # 72) on 05-28-2001, 09:49 PM:
Gord I think you are correct in that statement. I've never been able to find anything larger than 85 amps in a 1/4" stud size case. If he goes to 85A they will probably never fail.
Mark @ GTS
Posted by Paul G. Thompson (Member # 655) on 05-29-2001, 12:29 AM:
Gordon and Mark: You both have me wondering now. I bought two bags of those diodes about ten years ago. Today, I cannot find a current reference on them. I wonder if they were discontinued. I know they were 100 amp diodes, though. If I find a good number on them, I'll pass it along to you.
Posted by John T. Mellor (Member # 468) on 05-31-2001, 03:13 PM:
I have been using Diodes from a company called EDAL located in Conneticut Good diodes and very reasonable I will try to locate the phone number and post it as soon as I can We have been install ming the higher aperage 75 - 85 and most of the problems have disapeared I agree the only way to change them is to change all at once with hyeat sink grease. One of the problems we had experiance was that if someone was not shonw the proper way to change diodes we had a multitude of loose conections thayt led to premature diode failures.
I again will try to find the number for EDAL corp later todayRegards,
John
Posted by Paul G. Thompson (Member # 655) on 05-31-2001, 07:42 PM:
OK, Gordon and Mark, you are correct. The diodes were rated 85 amps. The ones I used were Italian doides, (number unknown) in a bag of 50 each. Unfortunately, I used them all up in the last 12 years, and the power supplies I used them in are no longer accessable for verification. I cannot recall at this time if I got those doides out of California, or Portland Oregon. 
Posted by Gordon McLeod (Member # 33) on 05-31-2001, 09:05 PM:
I find that Int. Rectifier are the most reliable