Film-Tech Forum ARCHIVE: Diode Change

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Topic: Diode Change

Gordon McLeod
Film God

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

posted 08-16-2002 05:59 PM

First things first did you measure the output of the rectifier no that it doesn't work
The Irem has a seperate boost supply. It is possible that it got disconected somehow in the process and the new diodes are working
If it reads somewheres around 30v out then the stack is working and the boost supply s diconected
Most Irems use all the same diode and I never found a mislabled one

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 06:05 PM

Darryl,

Perhaps they are not diodes, are a piece of pizza..

Thanks for the suggestions, I'll check them as you wrote.

Jean/Gordon,

I don't know. Since it is a Cinemeccanica Lamphouse I believe it is Cinemeccanica Style.
However I wouldn't search anywhere than diodes: before replacing them the lamp was working...

However, I'm curious. How could I check the no-load voltage? It can be useulf for future problems...

(Gordon, you posted your message while I was writing this one! Can you tell me how can I check the no-load voltage?)

Thanks to all

Antonio

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Gordon McLeod
Film God

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

posted 08-16-2002 06:11 PM

Locate the DC output terminals of the rectifier (the one with the two large cables atached) and with you meter et to DC volts measure the voltage across it

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 06:18 PM

Ok.

But what means "no-load"? Should I have to measure it with lamp in place?
A

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Gordon McLeod
Film God

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

posted 08-16-2002 06:20 PM

No ,load means rectifier on but bulb not lit

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Jean-Michel Grin
Expert Film Handler

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

posted 08-16-2002 06:23 PM

Maybe the igniter in the lamphouse (I know Only the DX 4 model) Is no powered or the neutral / live cable may be interrupted. Maybe you got a fuse inside the rectifier or in the console to power the igniter. check it them !
In manual mode (usualy the red button on the back of the lamhouse) work the igniter ?
To check the "no load voltage" is verry easy: Connect a voltmeter at the ouput of the rectifier, switch on the rectifier and if the lamp doesn't strike, you must measuring a voltage between 80 and 100 volts.

Good Luck !

------------------
Jean-Michel Grin - Europlex Cinemas (Switzerland)

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 06:24 PM

Ok, thanks. I'll check tomorrow. I have many to check!

Final question, will a rectifier damage itself if keep on with no load?

Thanks to all!!

Antonio

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Jean-Michel Grin
Expert Film Handler

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

posted 08-16-2002 06:27 PM

Normally not,

But discharge the capacitor before toutching it ! That's hurt really !

------------------
Jean-Michel Grin - Europlex Cinemas (Switzerland)

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 06:31 PM

Thanks for the advice.

How can I discharge the capacitor?

Antonio

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Gordon McLeod
Film God

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

posted 08-16-2002 06:37 PM

To discharge a capacitor use a large resistor to bleed off the charge.
Almost all rectifiers will have a bleader resistor across it IREM normilly does so after about 30 min it should have only about 5 volts across it that can be discharged with a piece of heavy wire shorting it out
The working voltage of the filter cap in the IREM is high enough that it should not be bothered by long period of being left on with out a ignition
THe odds are it is the boost supply that is down. There is a a small relay that controls it with it's own small bridge

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 06:45 PM

Do you believe that I have disconnected or touched it while changing the diodes?

Perhaps I remember what this relais is. There is a large relais inside the rectifier and a smaller one just above it. However I'll check for something disconnected inside the rectifier, where I can had accidentally touched.

I'll let you know!

Antonio

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Gordon McLeod
Film God

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

posted 08-16-2002 06:46 PM

The small relay is the control of the boost supply

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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 07:01 PM

Antonio:

When I talk about having the diodes "in reverse" I mean that the forward diodes look the same as the reverse ones. Also they could be labeled wrong.

I do not mean that you have wired or installed the diode backwards (or upside-down). I am talking about what the diode is made to do.

~Manny (When only the best will do.)

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Antonio Marcheselli
Phenomenal Film Handler

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

posted 08-16-2002 07:21 PM

Manny,

Ok, I will check also each diode polarity.

Thanks for your help!

Bye
Antonio

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Dennis Burns
Film Handler

Posts: 2
From: Midland, TX, USA
Registered: Jul 2002

posted 08-16-2002 10:41 PM

No spark usually means ... Igniter went boom... I know someone suggested that... but when you have a bad diode you still will get a spark... just not the voltage to keep it lit...

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