max capacitance of 1 cu ft box?

Have youi considered getting your head out of your ass and using a username that is a reasonable length?

Nick, The volume of the box has nothing to do with the dangers you describe. Large electrolytics with high working voltages are to be respected. Most modern equipment has bleeder resistors to discharge the caps. The static charge on the CRT can "surprise" you if you come in contact with the anode, after all it is a big "capacitor." If you are not that certain about procedures, educate yourself before opening the box. BTW: I don't know the position of your head with relation to your anus but I agree with JeffM. Regards, Tom

Weeks. The CRT itself acts like a capacitor and could store charge for several days or so. It is safer to get a long screwdriver with good insulated handle, heavy gauge wire, and 10 Mohm resistor all in series. Clamp the cable ro any ground (metal chasis of monitor usually works), and then work the screw driver under the suction cap on the CRT until it makes contact with the metal clamp inside.

You should do the same with each caps just to be safe. Even a $10 disposable camera with flash bulb carries a nasty kick if you touch the caps with your bare hand.

There is no foolproof system for determing the remaining charge of any CRT. I've been zapped by charged CRT and trust me you don't want to get shocked while carrying the CRT, they make a terrible mess when you drop them in reflex. :) Never needed medical attention yet but better safe than sorry.

PS really long email address. Try something shorter like snipped-for-privacy@aa.aa.

What is this about? The capacitance of the surface area of a volume such as a one cubic foot sphere or cube? Or the the capacitance internal to an electronic device such as the Mac SE? In the first case we are talking about

If you have to ask this question, you have no business opening an electronic device! There are warnings on the device about hazardous voltages inside and qualified techs getting into it. Heed the warnings! A tech will discharge hazardous caps to work on the circuits, but of course, he knows how to identify them and what to do. If you don't, keep out. To answer you question, some caps can hold there charge for a week or more so be careful. Bob

I've only done a few hundred PC monitors over the years, but typically, unlike TV's, they are discharged by the time you get the cover off, but..YMMV.

Tom

That is, the CRT is discharged. All bets are off for capacitors. CP01 (I think) in Thomson TX 85/86/825/826 were nasty ones. :-)

Tom

John's and Impmon's answers are likely the best. I'll probably just have to cautiously learn discharging and trust it won't get colorful. Thanx.

Tom Biasi and Bob, the dangers are precisely why I asked, and being knowledgeable before undertaking a procedure is precisely why I asked. I already agree with both principles. Having to ask a question is a qualification, not a disqualification; the necessity for asking comes from the nature of electrical circuits, and getting the information in advance is exactly what should be done when anything dangerous is undertaken. The lectures are better suited to those who don't ask. The issue to worry about is lack of judgment: the person who doesn't know what to ask when or when to turn back is the one who shouldn't do the work. I apply my expertise to many difficult problems and have refused various assignments when I saw fit to do so.

Tom Biasi, the size of the box proves little, but is a basis for inferring the possibility of there being more capacitance or less of it, all else equal, depending on intent, design, etc., since capacitors supporting more capacitance tend to be bigger. There's no practical way of knowing whether there's a bleeder resistor inside and whether it hasn't been dislodged or broken by past damage until it's opened, and I'm not sure I'd always recognize it anyway; the design isn't binding on used equipment.

Bob, internal capacitance is my concern, because that's the one that can be deadly. Carpet static and doorknob shocks are no worse than annoying or surprising to healthy adult humans, although the shocks can damage equipment.

Tom MacIntyre, I'm wondering if I was lucky when (based on one book) I waited an hour before opening a Mac SE, which I did many times, never with a shock from being too early. The SE is roughly a cubic foot. You might be lucky, too, based on other comments. Scott Mueller, author of Upgrading and Repairing PCs, suggests weeks as a possibility. On the other hand, it seems questionable why a designer would want more than an hour of usable capacitance, or more than a few minutes, for that matter, but maybe designs are only for minimum durations, not long ones, leaving us to allow for long durations, or discharge manually.

Jeff and Tom Biasi, the username was an error. When I registered with the newsgroup, I changed the default (the e-mail address as nickname) to Nick, then detoured through a link and came back to the registration page, and didn't check that the fields hadn't changed. (If it hadn't changed, Google or the newsgroup server goofed, but I'll assume I erred.) I changed it a moment after posting my message and seeing the ridiculous heading, but my subsequent change had no effect on that post. Maybe it will on this one.

Impmon, the e-mail address is real, although I prefer getting e-mail at my Yahoo address given in the message. I had intended a strategy of spam-resistance, but it doesn't seem to work, since I get more at Yahoo than at abcde.... My guess is someone out there manually reads posts for spamproofed addresses and figures out the real forms, then markets the list.

Thanx, all.

-- Nick

E-mail: Nick_Levinson Domain: yahoo.com