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Topic: Irem Rectifier Diodes blown up twice in one month!

Demetris Thoupis
Phenomenal Film Handler

Posts: 1240
From: Aradippou, Larnaca, Cyprus
Registered: Apr 2001

posted 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.

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999

posted 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

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 05-27-2001 10:55 PM

Also check your RF suppression capacitors. Better yet, replace them.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 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

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 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.

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Antonio Marcheselli
Phenomenal Film Handler

Posts: 1260
From: Florence, Italy
Registered: Mar 2000

posted 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

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 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

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 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!"

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 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.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 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

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 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

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 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.

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John T. Mellor
Film Handler

Posts: 52
From: Htafield, Pennsylvania, USA
Registered: May 2000

posted 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 today

Regards,
John

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 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.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 05-31-2001 09:05 PM

I find that Int. Rectifier are the most reliable

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