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Topic: Diode Change

Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 04:10 PM

I need your help.

On my Vic 5 I've changed the diodes, replacing the original 70A with 85A. Now the lamp doesn't strike... Or better, it doesn't try to strike.

If I turn on the rectifier (IREM) I hear the relais, I hear the typical "huum" but no strike at the lamp.

I'm quite sure that diodes has been replaced correctly. What could be happened? A faulty diode?

The only thing I was able to check was that the diode "array" was not electrically connected to the rectifier chassis. I have to disassemble all the array to test the diodes...

Any suggestions?

Bye
Antonio

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 08-16-2002 04:33 PM

Antonio:

Did you check all of the diodes or did you stop looking after you encountered a bad one? I just serviced a machine that had 2 bad diodes.

Did you check the new diode to ensure that it was good before you installed it?

You mention that the new diode doesn't exactly match the one you removed...maybe somebody with more experience can say whether that's the problem. FWIW the ones that I recently replaced weren't an identical match to what I removed...I'm sure there must be a rule to determine just how far you can stray before running into problems.

By the way, you did not mention the wattage of your lamp. Maybe you should provide that information in case it is needed.

The direction of the new diode is correct?
Also, about 2 weeks ago, somebody here on Film-Tech said that you should change them all at the same time.

~Manny.

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 04:39 PM

Hi Manny

I've changed them all. But I didn't check the new ones. Do you believe that a new diode can be faulty?

Question: let's suppose that one diode is bad. The lamp doesn't strike. What happen if I left powered the rectifier? When I realized that the lamp didn't strike I turned off the rectifier immediately. Can I damage the lamp keeping the rectifier on in my situation?

Bye

------------------
Antonio Marcheselli
Florence, Italy

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 04:43 PM

Manny,

I didnt' read fully your message or you edited it while I was replying you!

Lamp is Osram 3000W.
Diode direction... I believe there is no way to connect them upside-down

Bye!
Antonio

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 08-16-2002 04:44 PM

Antonio:

Yes. I believe a new diode can be faulty. I will agree that it is not likely but, whenever it is possible, it never hurts to check that any new part is really working before you spend time installing it.

As for diode direction - they come in two varieties: forward and reverse. You have to know which one you need.

~Manny.

The first brand new car my dad ever bought was faulty.
I got a brand new Dolby CP-45 with a faulty Cat. 512 board.

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 04:51 PM

Manny,

Thanks for your help. Tomorrow I'l disassemble the array and I'll check the diodes.

Ok, diodes are right. I've replaced the 72HFR100 with 87HFR120. Both are reverse.

ehm... I never checked a diode. A faulty diode is completely shorted (or completely open) or should I check the value that my tester says?

Bye
Antonio

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 08-16-2002 05:00 PM

Testing a diode to ensure that it only works in one direction:

Use your meter and if you get continuity in both directions (reverse the meter probes to check each direction) then you have a bad diode.

To be honest, I don't know if there is anything else you should check (values, or whatever). Maybe somebody else can make a suggestion about that.

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 08-16-2002 05:09 PM

Some diodes are isolated from the case, and you may have to do something extra to make sure the "case" side of the diode is connected properly. Did insolating hardware come with the new diodes, and you installed it, even though there was no insolating hardware on the old diodes? I found this done one time, and it disconnects the "case" side of the diode.

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 05:15 PM

Bruce,

What do you mean with "insolation hardware"? I have nothing between the "case" of the diode and the chassis of the array.

I'm also quite sure that the diode case is electrically connected to the array because I've connected the tester's probe to the array's chassis and to the diode and there is continuity. But I have continuity on both side of the diode (Again: tested while installed and connected)... Perhaps capacitors can distort the test?

Antonio

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Paul G. Thompson
The Weenie Man

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

posted 08-16-2002 05:35 PM

Sounds like you might have a reverse diode in a forward hole - or vice versa.

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 05:41 PM

Paul,

I'm asbolutely sure that all diodes are connected correctly. There is no way to connect a diode upside-down in an IREM (in my IREM I do not know the others!)

Do you mean that one of the diode can be forward instead of reverse? Uhm.... more and more unlikely... But I'll check!

Thanks for your help and... Would you tell me the way to have fast hair grow like yours???

Bye!
Antonio

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 08-16-2002 05:43 PM

In the CFS console rectifiers we have to use 3 forward and 3 reverse diodes. There is also a wire that hase to connect from the transformer to the center diodes in order for the lamp to power up. I am not that familure with the inside of the Irem rectifiers but wouldn't there be both forward and reverse diodes in use. you mention two diodes both reverse. Just a little puzzled here.

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 05:46 PM

Darryl,

I really don't know how the IREM works, I've just found 6 reverse (red lead) diodes in my IREM and I've replaced them with 6 reverse diodes!

Antonio

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 08-16-2002 05:50 PM

Antonio,

check the direction of your diodes with a multi meter. Do not rely on the lables on the diodes. These can be wrong.

Forward: place the black lead of the meter on the screw head of the diode and the red lead on the lead coming out of the diode. You should get a reading

Reverse: put the red lead of the multimeter on the screw end of the diode and the black lead on the lead coming out of the diode. You should get a reading.

when you check the be sure they are disconected from the unit.

hope this helps

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Jean-Michel Grin
Expert Film Handler

Posts: 222
From: Geneva & Lausanne, Switzerland
Registered: Jul 2002

posted 08-16-2002 05:56 PM

What kind of igniter have you in your lamphouse ? DC (like Strong models) or AC Like cinemecanica ?
Had you checked the no-load voltage at the output of the rectifier ?

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