Film-Tech Forum ARCHIVE: Diode Change

This is topic Diode Change in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Manny Knowles (Member # 1171) on 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.

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Manny Knowles (Member # 1171) on 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.

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Manny Knowles (Member # 1171) on 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.

Posted by Bruce Hansen (Member # 281) on 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.

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Paul G. Thompson (Member # 655) on 08-16-2002, 05:35 PM:

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

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Darryl Spicer (Member # 711) on 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.

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Darryl Spicer (Member # 711) on 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

Posted by Jean-Michel Grin (Member # 1360) on 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 ?

Posted by Gordon McLeod (Member # 33) on 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

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Gordon McLeod (Member # 33) on 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

Posted by Antonio Marcheselli (Member # 373) on 08-16-2002, 06:18 PM:

Ok.

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

Posted by Gordon McLeod (Member # 33) on 08-16-2002, 06:20 PM:

No ,load means rectifier on but bulb not lit

Posted by Jean-Michel Grin (Member # 1360) on 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)

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Jean-Michel Grin (Member # 1360) on 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)

Posted by Antonio Marcheselli (Member # 373) on 08-16-2002, 06:31 PM:

Thanks for the advice.

How can I discharge the capacitor?

Antonio

Posted by Gordon McLeod (Member # 33) on 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

Posted by Antonio Marcheselli (Member # 373) on 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

Posted by Gordon McLeod (Member # 33) on 08-16-2002, 06:46 PM:

The small relay is the control of the boost supply

Posted by Manny Knowles (Member # 1171) on 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.)

Posted by Antonio Marcheselli (Member # 373) on 08-16-2002, 07:21 PM:

Manny,

Ok, I will check also each diode polarity.

Thanks for your help!

Bye
Antonio

Posted by Dennis Burns (Member # 1366) on 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...

Posted by Dennis Burns (Member # 1366) on 08-16-2002, 10:44 PM:

But then again i am a Christie over loaded engineer...

Posted by Manny Knowles (Member # 1171) on 08-17-2002, 12:00 AM:

Welcome, Dennis!

I can sense that Brad wants somebody to tell you that you can edit any of your posts by clicking on the "edit" button above them. You don't have to post again just to add something that you left out.

True about getting a spark with a bad diode...but what happens if you've got a diode that's the wrong type? Either wrong voltage (amperage?) or polarity?

~Manny (squeeze your way to shapely hips & thighs.)

Posted by Steve Kraus (Member # 476) on 08-17-2002, 07:35 AM:

Wrong voltage (PIV): Depends "how" wrong. Either immediate failure or failure at some future point probably in response to a voltage spike.

Wrong polarity: Short circuit upon application of power.

Or, if we take this to the limit and have them all be exactly backwards (2 one way, 2 the other) you would have reverse polarity output of the rectifier and explode the electrolytic capacitors. And major damage to the xenon bulb if it managed to ignite.

Posted by Gordon McLeod (Member # 33) on 08-17-2002, 09:50 AM:

Denis since it doesn't try to strike it is more of an indication of a problem with the noload voltage.
Cinemecanica consoles have two different styles of ignitors one is a long open assembly usually mounted along the non operating side
The newer ones have a Irem ignitor in the reflector plenum box with a Brass rod comming forward for the lamp to connect to

Posted by Antonio Marcheselli (Member # 373) on 08-17-2002, 10:37 AM:

I found it!

I connected the probes to the rectifier output and I wasn' able to measure anything (just few AC current). So I decided to check again the diode array.

One diode support (lead side) didn't have the cork insulating. This is causing the array's chassis to be electrically connected with the diode's output (lead) and so (correct me if I'm wrong) feed AC power to the lamp.
The great thing is that I didn't touch that support! So the cork insulating was not there before! I've just thightened it (removing the thin layer of paint that has insulated it during these years)...

I've keept on the rectifier in this configuration only few seconds for each test. Can something be damaged?

Bye
Antonio

Posted by Gordon McLeod (Member # 33) on 08-21-2002, 09:54 PM:

If the lamp didn't light and the filter cap didn't go bang all should be fine
Is it working satisfactorly now?

Posted by Antonio Marcheselli (Member # 373) on 08-22-2002, 03:54 AM:

Gordon,

Yes, it works perfectly now! I can't explain myself how can has worked since now without that thing...

Thanks to all for the help!
Antonio

Posted by Jean-Michel Grin (Member # 1360) on 08-22-2002, 05:27 AM:

Congratulations !

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

Posted by Manny Knowles (Member # 1171) on 08-22-2002, 06:57 AM:

Antonio:

I have a projector that had a random jumper wire in place and it worked for three years and then -- nothing. It took a short while to isolate the area where the problem existed and then when we came across that wire it was hard to believe that it ever could have worked. Sure enough, removing that jumper solved the problem.

Like yourself, I have no idea how it ever worked in the first place.

~Manny (a taste of the islands.)

Posted by Mark Gulbrandsen (Member # 72) on 08-22-2002, 07:38 AM:

Antonio,
Heatsinks are not painted, but anodized black, clear, gold,or what ever color, This is very common, Anodizing is a very good insulator itself if thick enough, just the anodizing itself probably afforded you the insulation for that duration till you tightened it up and pricked through it.
Mark