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Author Topic: Discharge the CRT?  (Read 5617 times)

Offline jepinto

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Discharge the CRT?
« on: September 09, 2003, 02:35:36 PM »
I'm about to replace the video/analog board on an iMac 333

"jen-how do you get into these things?  Are you NUTS?  Didn't you ever learn to say NO?"

"Hey, he's a good friend, and you know, since the stroke..... And it's a learning experience, and it is our responsibility to "spread the word" and, and"

"But a video/analog board? What do you know about EMI and discharging a CRT, and making sure you're not a open circuit.."

"Well, there's two schools of thought here.  One says the instructions "Discharge the CRT" is  a liability issue, you know CYP (patootie), and the other says that you can even blow the CRT and cause an implosion rivaling the Big Bang in magnitude...."

So the question is
1. Does the CRT really require discharging?
2.  Does discharging the CRT "blow" the CRT?  Or is more along the lines of crossing the poles on a bad solenoid so you can start the car "one more time"?

-Bad spelling edit-
« Last Edit: September 09, 2003, 07:39:38 PM by jepinto »
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Fear those who do not care; they neither kill nor betray, but betrayal and murder exist because of their silent consent.
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Offline Epaminondas

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Discharge the CRT?
« Reply #1 on: September 09, 2003, 04:01:04 PM »
<< discharging a CRT >>


If you are talking about fooling around the back of a naked CRT,  you are dealing with high voltage that can kill you.

No one has any business fooling around with a naked CRT unless they know exactly what they are doing.

Other than that - I wouldn't worry about it.


There are home repairs and there are times to take a Mac in to the repair shop.


Best regards,

Epaminondas
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Offline Bill

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Discharge the CRT?
« Reply #2 on: September 09, 2003, 04:04:20 PM »
Lorraine ... Make room for Jennie Quick!!!
She's talking to herself again! biggrin.gif biggrin.gif
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Offline bobw

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Discharge the CRT?
« Reply #3 on: September 09, 2003, 06:08:37 PM »
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Offline Xairbusdriver

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Discharge the CRT?
« Reply #4 on: September 09, 2003, 09:05:13 PM »
Just so you'll have something to do in the hospital, go to all these links and print them out!

Shoptalk
LowEndMac
Apple's Troubleshoot and Repair Many other links here from the 'core!'
This one is REALLY scary!

Jim C.

I love the understated comments like: "Discharging the CRT before repairs will lessen the chance of electrical shock [and DEATH jawdrop.gif ] oops.gif  whistling.gif
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Offline kelly

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Discharge the CRT?
« Reply #5 on: September 09, 2003, 10:06:20 PM »
I don't recommend it Jennie. It's not worth it. huh.gif

I haven't checked all the links.

But shops have tools to discharge it safely. You don't.

Trying to fix an old Tube TV 25 years or so ago.

I touched something I shouldn't.

It knocked me across the room and burned a little permanent scar on my finger.

I didn't do that again.  huh.gif
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kelly
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Offline jepinto

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Discharge the CRT?
« Reply #6 on: September 09, 2003, 10:22:53 PM »
Ok, ok, OK y'all have convinced me NOT to do it.

Now wadda I do?  It's in parts and pieces, new part sitting there calling to me......
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Do not fear your enemies.  The worse they can do is kill you.  Do not fear friends.  At worst, they may betray you.
Fear those who do not care; they neither kill nor betray, but betrayal and murder exist because of their silent consent.
~Bruno Jasienski~

Offline kelly

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Discharge the CRT?
« Reply #7 on: September 09, 2003, 10:26:35 PM »
So. How did you not get killed taking it apart? smile.gif

Call a shop and ask them what you should do.

All they should charge is the labor. No? smile.gif
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kelly
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Offline jepinto

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Discharge the CRT?
« Reply #8 on: September 09, 2003, 10:45:06 PM »
I stopped at the "discharge the CRT" stage.  The rest of the iMac is in pieces, we're now down to the diconnect and put in new board stage.

Problem is finding a shop.... there's one chance in less than 60 miles.  And only if he is willing to take it on....  I'll find out Wednesday.
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Do not fear your enemies.  The worse they can do is kill you.  Do not fear friends.  At worst, they may betray you.
Fear those who do not care; they neither kill nor betray, but betrayal and murder exist because of their silent consent.
~Bruno Jasienski~

Offline Epaminondas

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Discharge the CRT?
« Reply #9 on: September 09, 2003, 11:30:08 PM »
<< Now wadda I do? >>
 
 
Don't touch it. Don't let anyone else touch it.
 
 
The biggest danger here is to the visiting friend, neighbor, or grandchild. A note to "Do Not Touch" will likely have the opposite effect on any intrested, inquiring mind.
 
 
The capacitors associated with a CRT store considerable current, even when the CRT is unplugged for considerable periods. I have heard one story (Internet) similar to Kelly's involving an old CRT that had been stored in the attic for several years. The assumption was that the charge had dissipated in the interim. Wrong assumption. Knocked the guy on his rear - thankful to be alive. The guy seemed credible - tough ol' no-nonsense fixit type. True or no? I choose not to seek the answer question scientifically.
 
But I do know for a fact that it really is hard to perform CPR on yourself. Particularly when you are unconscious at the time.
 
 
You got yourself into this one, Jennie. I'm sure you will find your way out.
 
 
Do take care,
 
Epaminondas
« Last Edit: September 09, 2003, 11:33:19 PM by Epaminondas »
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Offline sandbox

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Discharge the CRT?
« Reply #10 on: September 10, 2003, 12:25:58 AM »
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Offline Dreambird

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Discharge the CRT?
« Reply #11 on: September 10, 2003, 01:55:40 AM »
Think it's worse than just talking to herself Bill... she says she hears puter parts calling to her. whistling.gif

BTW...

jen-how do you get into these things?  Are you NUTS?  Didn't you ever learn to say NO?
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Offline gunug

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Discharge the CRT?
« Reply #12 on: September 10, 2003, 07:56:41 AM »
I'm someone who has swapped out a bunch of CRT's and I can remember back to the original Apple tech references that showed using a screwdriver with a wire wrapped around the top of the blade with the other end hooked to the chassis ground of the CRT. . .that's if you don't have the "official" discharge tool.  A tool can be something not much different than the screwdriver (generally they involve a large resistor).  I have "yet" to be shocked in the process of changing out a CRT but it is something that requires care!
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Offline Xairbusdriver

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Discharge the CRT?
« Reply #13 on: September 10, 2003, 04:18:11 PM »
QUOTE
Apple tech references that showed using a screwdriver with a wire wrapped around the top of the blade with the other end hooked to the chassis ground of the CRT.

But that's not the complete description of the tool. Read the links, one of them is from Apple and describes how to construct this type of tool. It recommends a 10megohm resistor. That's not a very conventional, in-most-scrap-box resistor! If you simply use a screw driver (or some other metal object) you will likely damage some thing on the mother board and quite likely your self! oops.gif Probably will melt whatever that object was, also...

This is not rocket science, but you must know what you are doing to do it safely. It is one of those things Mr. Wizard used to say, "Kids! Don't try this at home!" Which, of course, created lots of terror in many homes! rolleyes.gif  biggrin.gif

Jim C.
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Offline gmann

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Discharge the CRT?
« Reply #14 on: September 10, 2003, 06:17:41 PM »
It is a very simple procedure. Use a insulated lead with alligator clips at both ends. Clip one end to the shank of a slender screwdriver and the other end to ground (metal chassis will do) Slip the screwdriver under the pubber suction cup on the side of the CRT, making contact with the end of the hi-pot lead. you may or may not hear a snap sound. This action will discharge the high voltage. You then can lift the edge of the cup and unclip the end of the lead from the pit in the side of the CRT. If you have rubber gloves (dishwashing type) it may give you a sense of security.  I used to have a TV repair business and perfomed this simple task several times a day.
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