Discharging CRT?

Hey,

Huh? That's ridiculous. Some people have to imbue even the easiest tasks with some sense of drama or danger. You have been ill-informed. I've been inside scores of toasters and I never discharged a single CRT. The tools you need are a 9" T-15 torx driver, a philips head screwdriver and the service manual for the SE. A steady hand and a cool head wouldn't hurt either. Get the manual at the mirrored gamba site.

Hey,

You do NOT need to discharge the CRT to replace a harddrive in a Mac SE. The T-15 Torx tool is for the four case screws: two on the back bottom, two in the handle recess (hence the need for the 9" or so). The philips head is for the screws that hold the harddrive/floppy assembly to the mobo and for the screws that hold the harddrive to the assembly. If you're a true noob get the service manual. If you don't, you're a true boob.

Remember that AF is not responsible if or when you get hurt for not discharging the CRT. The service manuals for ALL of the compact Macs say to discharge before working inside them, and it is AF's opinion that one should follow the manual's warnings.

We've been through the discharge/don't discharge bit many, many times, with most if not all of those times ending in a flamewar. And if this thread starts heading in that direction, you know what an admin's gonna do.

I gotta say my experience parallels that of williamahearn, I never discharge the CRT before doing stuff like HD or MLB swaps. Still, one should always be verrrrry careful around any high voltage components. From the Larry Pina repair books I learned a basic technique for such situations - by keeping one hand behind your back, it's much harder to actually kill yourself if you do accidentally collect some stray HT volts.

BTW, the SE and later classic Macs have a discharge circuit built-in which bleeds off the stored charge within a few minutes of being powered down.

dan k.

So, to be the only one who actually attempts to answer your question, here goes.

Basically put, you want to slide a metal probe under the suction cup on the back of the CRT and touch the metal contact in the middle. The probe is connected to ground and not you. If you don't have a high voltage probe handy, a long screwdriver will work if you attach a aligator clip lead to the shaft and connect it to the computer's chassis. Just make sure you aren't touching any metal part of the screwdriver.

The Voltage on the old toaster macs is only 9000V so it's not quite as dangerous as large color monitors. However, one compelling reason to dischage the CRT other than personal safety is to protect your machine. I once saw a guy stick his hand into the machine to get the floppy drive out, got zapped, and jerked his whole arm out. In doing so, he cracked the CRT neck enough to let air in, and cut his hand open pretty good on something sharp.

As a side note, if you do this, please record it. We all thought it was pretty funny.

I had a 21-inch Monitor that I was working on, an shocked myself in the process of trying to tune the darn thing. I hit a large (and I do mean the size of a fist) Capacitor, and was lucky to get my hand out of there. (i was in pretty far due to the fact that the idiot that designed it decided to wedge the tuning controls between the front of the CRT and the board below it.) I ended up shocking myself so bad that my arm twitched so violently the my skin started peeling the next day 'till it was starting to bleed. I still am having so loss of feeling on the part that hit the capacitor.
On another note, my dad has met electicians that test light circuits in large buildings that are being built that have been shocked so many time on their hands, that they don't even bother with using equipment to test if there is power or not. They just lick their thumbs (and I do mean lick thums) and put it into the light socket. If they feel a buzz( which I imagine is pretty hard to feel after frying their brain), they know the circuit is active. If not, then go back and chech the wiring.

It'll recharge the first time you turn it on. It's not really like a battery.

BTW, the SE and later classic Macs have a discharge circuit built-in which bleeds off the stored charge within a few minutes of being powered down.

That's assuming the circuit is working. When dealing with that much voltage, it's a good idea to discharge anyway, just to be safe--and is why service manuals continued to advocate discharging after the circuits appeared.

When discharging my Colour Classic about a million years ago, I couldn't get the anode cap to come off. This is probably a bit off topic, but how much force should it take to pop it off, and what's the best way to do so? I ended up throwing away the whole CRT+Analogue Board assembly.

And as long as you aren't touching metal while discharging, and your discharging tool is properly constructed, you should be fine. Then again, I've never worked in a SE.

The anode cap has a clip which sticks out to the sides within the crt. To remove it, you squeese the two metal plates togather and lift it off, this is best done using insulated pliers.

If you're discharging the CRT with a screwdriver, you can also use it to push one side of the anode clip in, and it'll pop out easily.

I have just taken eMac apart few weeks ago. Here is the picture that shows the clip removed.

http://www.lbodnar.dsl.pipex.com/eServer/L-IMG_0657.JPG

That makes it a lot clearer to me, thanks.