I have an iMac G3 that I'm planning on playing around with but need advice on handling the CRT and how to make sure I don't kill myself.

I have read quite a lot about discharging the CRT and the one thing I'm not sure about is how to make sure that when discharging you have the tool properly grounded.

Do you keep the computer plugged into the mains, but with it off, so the earth connection is still attached and thus used when discharging.

Where is the ground lug, which seems to be referenced in a few resources, such as this one, as I want to ensure I'm connected to the correct bit, so I don't become the ground.

Will wearing electricians gloves (or gloves suitable for handling high voltage) help protect me when doing this, or will they end up being cumbersome and give a false sense of protection?

Is it a good or bad idea to wear rubber soled shoes, will this also help insulate me, or again give a false sense of protection?

I guess the more precautions the better, but just trying to figure out what's actually helpful and what's not.

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    Thanks for asking this - it's a good question and one that others can use. I love encouraging people to be curious and safe at the same time. – bmike Nov 12 '12 at 1:30

I can verify that the advise in that article is correct. I have discharged and serviced CRT Macs.

I personally am not going to give you any safety advise as it is a potentially dangerous process and should not be undertaken if not confident. I would avoid servicing these machines especially if you do not have access to the official service manual.

  • Thanks for the response, guess if you're unwilling to give advice, that's a good enough sign that I shouldn't be messing with it. Didn't quite realise how dangerous it was until I started reading up. – andyface Nov 12 '12 at 1:24
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    :) glad I've convinced you. I've seen the results of it going badly, it's not good. – Justsomeguy Nov 12 '12 at 5:21

The link to safety precautions is very high quality and I can't find anything wrong with what it says.

As to going into a Mac with a CRT, if you are not sure you have a good ground, hire an electrician to ensure your path to ground can take an CRT discharge voltage and current safely before proceeding.

Many trade schools offer electrical safety classes to the public, so look for one and make sure someone trained is there to observe you from a safe distance the first time you attempt a CRT discharge.

The good news is a CRT capacitor has one good shock in it if you are not connected to the mains while working on it, so the person observing only needs a cell phone to call for medical attention if you get shocked. If you are going to mess around with it connected to the mains, give them a wooden pole long enough to knock you away from the device or to dislodge the power if things go badly.

The bad news is this shock isn't one you want to have cross your body and hit your heart since you don't need much current to cause death and the high voltage that can be contained inside a CRT makes it likely the current will jump to ground if offered the chance. You want to do all you can to ensure that your body is a worse path to ground than your grounding device.

I would find someone who has done this before as a TV repair tech or a computer tech and not try to learn this yourself. Even when you are trained, never work on these alone.

  • Thanks for the response. Sounds like the best thing to do is stay the hell away from it. – andyface Nov 12 '12 at 1:26
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    I've been shocked many times when I worked as a diver in the US Navy and it's not fun. Underwater welding, salt water, generators, electrical equipment, CRT, radar and such made many chances to come to harm when dealing with electricity. Learning to work in CRT is serious but very doable. I would recommend spending more time learning how other electronics work as you'll spend a lot of time learning to be safe with a CRT for some soon to be antiquated skills about older hardware. You could learn how to work on them, but most people don't need this skill and can safely just stay away. – bmike Nov 12 '12 at 1:29
  • yeah, been shocked a coupla times myself, not something I want to repeat. May look into some kind of electronics course as I know I'd enjoy it. Thanks for your input. – andyface Nov 13 '12 at 19:49

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