5 Feb
2011
5 Feb
'11
1:29 p.m.
On electronic (i.e. personal computer) gear, I
wonder if the role of
the ever-present ground wire isn't more for RF noise than actual
safety protection.
Possibly. Althoguh a lot of computer equipment is metal-cased and
certainly wouldn't meet the requirements for double insulation. One
consern would be the mains filter. With no ground wire the casing would
flaot at half mains voltage due to a capacitive voltage divider formed
from the capacitors from the power-carrying wires to the case. Yes, the
source impedance would be quite high, but enough to give you a tingle.
Worse than that, if you connect the machine ta an earthed device and if
the logic ground wire is defective you are most likely to end up zapping
driver and receiver ICs. This was, I am told, a problem with some Acorn
Econet installations...
6 Feb
6 Feb
8:01 a.m.
It's happened to me :-( I have a Vaxstation 3100
which was equipped with an
Ouch :-(
SPX graphics adapter which was plugged into a very
nice VR297 monitor (Sony
Trinitron). I plugged out the monitor cable from the back of the Vaxstation
for some reason. When I plugged it back in I felt a zap. On investigating,
the earth pin in the IEC plug going into the monitor didn't seem to be
making proper contact for some reason. The monitor didn't mind a bit but one
I've neve seen that happen. Normally it's due to a wire having fallen off
in one of the connectors. Of course tend to prefer the rewirable IEC
sockets so I can check the wiring and make sure the contacts aren't bent
open/
of the primary colour outputs from the SPX adapter
went away (red I think).
I traced the connections on the graphics card and found the RGB outputs came
directly out of a large, probably expensive, difficult to replace and rare
looking BT459 RAMDAC :-(
I asuem that's a Brooktree part from the number. They are not mormally
custom chiups, you even find them (although probably not the right one)
on old VGA cards.
That was the only serious problem I ever had with them but I never liked IEC
plugs and sockets much. Even when they are correctly mated, they often seem
loose. I suppose on the plus side, they are more likely to pull free than
cause damage when I trip over a mains lead...
There is a locking assembly avaialble, but few manufacturers seem to use
it. And it doesn;t work with moulded scokets (see above ;-)).
What mains connector do you prefer?
-tony
5068
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5069
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