Cracking open an Emac - Deadly CRT Discharge

Posted by: wyclef

Cracking open an Emac - Deadly CRT Discharge - 05/30/07 03:43 PM

hey, i'm crackin open an emac to swap out the optical drive and hard drive and just want to doublecheck to see if I can do this without discharging the CRT? since i've never done this before, and am aware of the deadly risks yet plan to do this anyways and read this article yet will still probably fry myself i was wondering if anyone could offer some homebrew advice for a noob. I'm doing it regardless of the risk so give me some good advice.
Posted by: TCPMeta

Re: Cracking open an Emac - Deadly CRT Discharge - 05/31/07 05:56 AM

Avoid the cable going to the CRT to the power board. Also avoid the big black box on the power board. I would discharge it.

Heres a nifty idea. Get a old power cord and cut off the two main prongs and tape them off. Leave the ground 3rd prong on. Plug it into a outlet for 10 seconds. Just prey your outlet has a common ground so it will discharge. If the outlet doesn't have a common ground then it will not discharge.
Posted by: modyourmac

Re: Cracking open an Emac - Deadly CRT Discharge - 05/31/07 08:29 AM

I would say that the short answer is no, you dont need to discharge the crt.  All the work you'll be doing is on the other side of the analog display assembly, so you wont be near the anode aperture, or anode cap. The closest you'll get will be removing the main rear fan assembly. So, bearing that in mind, pay attention to what you do touch, make sure not to touch other things, and you should be all good.

however, should you want to discharge that puppy, got a long handled screwdriver, and some wire with alligator clips. clip one end to the screwdriver, and the other end to the heat sink on the computer's chassis. Use the screwdriver to pry up the anode cap, and rub its contacts thoroughly. then, do the same to the anode aperture. Be careful though, as you dont want to be wearing a wrist strap when doing this. likewise, if you let it sit, you may want to discharge again, since the charge can build back up.
Posted by: Waragainstsleep

Re: Cracking open an Emac - Deadly CRT Discharge - 05/31/07 08:32 AM

You can remove the optical drive without discharging the CRT. Just don't touch the tube or the power board..
Posted by: wyclef

Re: Cracking open an Emac - Deadly CRT Discharge - 05/31/07 09:22 AM

Cool. I'm not gonna discharge the CRT. I'll just power down and leave it unplugged for 24 hours. I also need to replace the HD but that's on the same part as the optical drive so it should be good. If the machine is unplugged for awhile shouldn't the charge dissipate?
Posted by: manhackman

Re: Cracking open an Emac - Deadly CRT Discharge - 05/31/07 09:38 AM

Originally Posted By: "wyclef "

Cool. I'm not gonna discharge the CRT. I'll just power down and leave it unplugged for 24 hours. I also need to replace the HD but that's on the same part as the optical drive so it should be good. If the machine is unplugged for awhile shouldn't the charge dissipate?


Some circuits are set up to do that.... I think.  But I've got no idea whats going on inside the eMac.  The prob is that the consequences of being wrong are pretty severe.  I tried to discharge the CRT in my Mac Classic II with a discharge tool I borrowed from some friends and I'm sure I broke something in the process.  I was just gutting the case so it didn't really matter.  I like TCP's  prong clipping method.  I'd leave it unplugged for a couple days, and do the prong thing and avoid the sensitive areas ( and I'd wear a jock strap and cover my head in tinfoil too). SAFETY FIRST!
Posted by: wyclef

Re: Cracking open an Emac - Deadly CRT Discharge - 05/31/07 10:35 AM

i didn't understand TCPs idea? wrap an old power cord around my tongue, stick a fork in a socket and put one foot in a bucket of water?
Posted by: TCPMeta

Re: Cracking open an Emac - Deadly CRT Discharge - 06/02/07 05:39 AM

Last time I try to help you.
Posted by: zenstate

Re: Cracking open an Emac - Deadly CRT Discharge - 06/02/07 06:12 AM

Originally Posted By: "wyclef "

Cool. I'm not gonna discharge the CRT. I'll just power down and leave it unplugged for 24 hours. I also need to replace the HD but that's on the same part as the optical drive so it should be good. If the machine is unplugged for awhile shouldn't the charge dissipate?


after only 24hrs the crt will still have loads of current sitting in it.  enough to kill or seriously mess you up at least.  a crt has to be unplugged for at least a couple months before it will totally lose its built up current.

its doesn't seem like you really know whats up (no offense) so you shouldn't go poking around inside.  you need to put this project on hold and do a bunch os research.
Posted by: Waragainstsleep

Re: Cracking open an Emac - Deadly CRT Discharge - 06/02/07 11:16 AM

Originally Posted By: "wyclef "

i didn't understand TCPs idea? wrap an old power cord around my tongue, stick a fork in a socket and put one foot in a bucket of water?


I thought that was hilarious.

Discharging a CRT is not hard. Google it
Posted by: MDC

Re: Cracking open an Emac - Deadly CRT Discharge - 06/04/07 07:07 AM

Originally Posted By: "wyclef "

i didn't understand TCPs idea? wrap an old power cord around my tongue, stick a fork in a socket and put one foot in a bucket of water?


made me chuckle for sure. smile I hate to admit it but I have had had a disassembled iMac sitting waiting for a mod, just because I haven't discharged the crt to get to the a/v board and power supply. :shrug:
Posted by: Waragainstsleep

Re: Cracking open an Emac - Deadly CRT Discharge - 06/04/07 12:05 PM

TCP is right though. If you pull the live and neatral pins from the plug (thats what we call what we have in the UK), then you are left with just the ground. That way the machine can discharge but there is nothing charging it back up again. That should discharge quicker than just leaving it.
I'm not familiar enough to know whether pressing the power might speed it up even further in this case.
Wouldn't plugging it into a socket which is powered off have the same effect? It would seem pointless to have the ground connected to the on/off switch.

Essentially you just have to short the anode to ground. You will have no trouble spotting the earth strap if you take the case off, the anode is under a rubber cap at the point of the rear of the tube. Right in the middle with a big cable attached to it. You just have to poke something metal (with a plastic handle) under the rubber cap, and attach it (usually with a crocodile clip on a wire) to ground. You can attach the clip first then just poke the anode and you're done. A long screwdriver is perfectly good for this.

Its worth noting that discharging a CRT is the one act of computer repair for which you should NOT wear a grounding strap. If you are particularly worried, stand on an old tyre or a rubber mat while you are doing it.
Don't expect the earth to move. I believe if you hunt around you will find another thread detailing the anti-climax that is discharging a CRT.
Posted by: waamatt

Re: Cracking open an Emac - Deadly CRT Discharge - 07/06/07 08:38 AM

I thought there was some fun way of actually sticking something into the CRT to discharge it. I'm serious, by the way. It's either a screwdriver wrapped in something, or a pencil. I wish I could remember where I saw that. Maybe it was on this site!
Posted by: modyourmac

Re: Cracking open an Emac - Deadly CRT Discharge - 07/06/07 09:24 AM

Honestly, Waragainstsleep, just stated how to do it. Its actually very easy. However, and I'll say this again, when working on an emac, it is usually unnecessary. The CRT and the analog video board are shipped by apple as a complete assembly. you remove the housing, and depending on the model, maybe the speaker assembly. You pull off the back grille and remove the logic board/drive assembly, and you're left with the analog display assembly, held to the front bezel with less than a dozen screws around the edges. You remove those screws, and you can pick up the display assembly by the plastic hoops on either side. Then you set it aside.  You've just taken apart an eMac.

Now, lets assume you want to dig into the analog display assembly. then you DO want to discharge the CRT. I'll explain in detail.

1. find a flat blade screwdriver.
2. find a piece of wire with alligator clips on both ends.
3. clip one end to the screwdriver.
4. clip one end to the heat sink on the assembly, or to the metal framing.
5. make damned sure you arent wearing a wrist strap.
6. on the back of the CRT, look for the large black suction cup thing, that has a wire sticking out of it.
7. pry it off with the screwdriver.
8 rub the cap's contacts with the screwdriver
9. look at the CRT. see the inverted nipple in the glass? thats the aperture. carefully place the screwdriver against the metal ring thats embedded in the glass, and rub it around in the aperture. It may spark, it may not. It will most likely be very anticlimactic. However, you've just bled out the charge. If you set your work aside for a bit, discharge the anode aperture again.
10. when done, and reassembling, pull back the anode cap with your fingers, so you can see the attachment prongs. seat one, and then use the screwdriver with wire to press the other in place. Then let go of the cap, and it will flip back into place.

If you've done all this correctly, you should 1. have removed an anode cap and discharged a CRT. 2. you should have gotten your work done, and replaced the anode cap back into the aperture. 3. you should still be alive, unelectrocuted.

Mind you, when you get tested for Apple's desktop certification, they test you specifically on ESD (electro static discharge). There are 12 questions. if you dont get a majority of them right, you automatically fail. Why? Stupidity with electricity can KILL you. Mind you, this procedure is easy, and I've done it countless times. However, its one of those things you should always pay attention when doing. The last thing your girlfriend, mom, etc wants to find, is you slumped over a half finished project, dead, having vented your bowels into your pants. So yeah, be smart, not stupid smile
Posted by: techspeak1

Re: Cracking open an Emac - Deadly CRT Discharge - 10/05/08 06:22 PM

All I can add to this topic of discharging a CRT is: Be Careful!