What fun from a Macintosh SE

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Aug 20 18:20:06 2004

> >> There are dangerous voltages on the analog board of that machine.
> >> Perhaps even FATAL voltages.
> >
> > You're more likely to get hit by a car than get zapped by your
> > Macintosh
> > if you take simple precautions, like unplugging it from the wall for
> > example.
> Yes I already know to unplug it and let it sit unplugged overnight or
> for
> a few hours at least. The CRT is a big capacitor and if it is not

It's actually a fairly small capacitor electrically, the problem is it
charges up to about 12kV (it is used as the smoothing capacitor for the
EHT supply, of course).

> properly
> drianed it can throw you across the room. (well at least TV crts can.)

However the charge is unlikely to be fatal. I have been zapped a couple
of times, the worst was from the EHT supply in a Barco monitor when the
unit was switched on, and when a transistor on the EHT regulator PCB had
failed so the EHT was sitting at about 32kV. It deceid to flash over to
my fingers. And yes, I lept across the room.

However, it is _darn hard_ to connect yourself to the EHT in a Mac (or in
any other monitor) unless you are working on that area. The EHT connector
has a nice insulated rubber cover on it. The EHT rectifier is inside the
flyback transformer -- there are just no bare connectiosn to touch. The
only problem comes if you disconnect the EHT connector from the CRT to
remove the CRT or the analogue board (or replace the flyback

Received on Fri Aug 20 2004 - 18:20:06 BST

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