Re: hot plugs

[Reza Naima <reza.reza@net>]

my favorite time getting shocked was when i was playing with the phone wiring
outside my house, bare feet in a pool of water.  a phone call came in upping
the juce on the line (something like 5v->35v with decent watage.  I few
back. fun)

reza

On Fri, Feb 05, 1999 at 01:05:34PM -0800, Dalvenjah FoxFire sent me this...
> On Fri, Feb 05, 1999 at 12:30:44PM -0800, Jim Serio put this into my mailbox:
> > 
> > Do MB's have some sort of circuit breaker? On many
> > a occasion, while working on mine, I've pulled cards
> > or dropepd screwes and hit something that caused the 
> > power to shut off. Immediatly trying to switch it back
> > on results in nothing, but waiting a minute or so
> > seems to resolve the problem. I assume either the 
> > PS or MB have some sort of circuit protection and
> > some sort of timed breaker?
> 
> I think most PC-type power supplies have some sort of cut-out that
> does this; and yeah, they 'reset' after a minute or two.
> 
> > On a related note, while talking with a co-worker
> > who was studying for his A++ cert, one of the
> > questions is soemthing like:
> > 
> > To discharge the capacitor in a monitor, you need to:
> > A. do nothing. There is no power when unplugged
> > B. Wait 24 hours
> > C. use a screw driver to short it
> > D. ?
> > 
> > Anyway, the correct answer is/was C! Has nayone tried
> > this? I imagine Carl or some other CE/EE could confirm,
> > ut I'd think you'd fry your ass off, or at least get a jolt.
> > On a related note, I've heard that power supplies, while
> > they do retain some juice even when unplugged, only
> > offer a good jolt if you open them and touch somethign you
> > shoudln't (before discharging it). But it's apparently non
> > life-threatening. Confirm?
> 
> Depends. Don't try it. }:>
> 
> The first thing you do when opening anything with a high-voltage
> picture tube is indeed to discharge the high voltage supply. There
> are special tools for this; the most common is a thin metal spike
> with a wire that looks like a spark plug lead leading to a ground
> clamp; the spike has a 2-inch-diameter rubber handle around it.
> You connect the ground clamp to a good ground, then wedge the spike
> under the high-voltage connector's rubber gasket, touching the
> metal connector post, to discharge the supply.
> 
> Note: keep ALL your body parts away from any type of ground or
> metal thing, including static ground straps, while doing this; I once
> did this operation on a Mac Plus while holding my hand next to a metal
> part of the case. Despite the two-inch-thick rubber handle, I
> managed to send a spark across the half-inch gap between my hand
> and the metal portion of the case; the display would have been cool
> were it not extremely painful.
> 
> It's generally a good idea, when working around things with large-capacity
> or high-voltage capacitors, to discharge the capacitors before handling.
> Assuming the power supply is turned off and unplugged, the shock
> will most likely not be life threatening, just painful; I do not
> recommend anyone risk it, though. (over the years, I've managed
> to shock myself with everything from 12V while starting a car, to
> 277VAC (commercial fluorescent light applications), to high-voltage
> spark plug and CRT voltages. I've miraculously survived so far, but I
> don't relish the idea of getting shocked again, and certainly have
> the memory of many different shocks to know that taking precautions
> not to get shocked is a Very Good Idea.)
> 
> Just to be safe, before working with power supplies, unplug it, and
> using a relatively thick wire, connect any voltage-bearing metal part
> to ground to drain it. This can and should include the metal grounding
> part of the power supply's case.
> 
> -dalvenjah
> -- 
>  Dalvenjah FoxFire (aka Sven Nielsen) "We've lost the bleeps, the creeps,
>  Founder, the DALnet IRC Network       and the sweeps!" "That's not all
>                                        he's lost!"
>  
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