7 Oct
2001
7 Oct
'01
1:19 p.m.
At 19:31 07/10/2001, you wrote:
lab.... :)
It's worth asking. Really you need to anneal it after bending it to
shape (bending it will affect the magnetic properties and will make it
less good as a sheild). But in practice if you don't bend it except at
the corners where you have to, it will be a lot better than nothing.
Anneal - is that where you heat it up & hit it with a hammer? Or do you
just heat it up and let it cool again? I forget now... It's been a long
long time since I had any metalwork lessons.
Well, a screwdriver bit. It's one of those 1.5in long bits which go into a
handle, or drill.
Aluminium won't do a darn thing about 50Hz magnetic
fields. You want
something like mild steel, or better still mu-metal (if you can get it at
a sensible price, or indeed, at all).
Okay, that makes sense. I *should* be able to get hold of some of this
"mu-metal" stuff - I know people at an electicity/electronics R&D
I will have a poke around with my multimeter tomorrow...
In another post you mentioned you could easily detect the stray field
with a screwdriver (ouch!). OK, take the loads off the transformer. Pull the power
connector off the
mainboard, and unplug the cable to the monitor. Is there still the same
stray field (if so, suspect shorted turns or similar in the transformer).
Yes, it's still there, albeit not quite so strongly. Still enough to induce
a noticable vibration in my magnet-on-a-stick.
If not, then reconnect one of the loads (say the
mainboard) and see what
the field is like now. Then try connecting the other load (monitor) on
its own and see what the field is like.
If one of the loads causes a rediculous increase in the field, then check
the rectifiers and smoothing capacitors in that section...
No, not ridiculous (at least, I don't think so), but there is a noticable
increase when the monitor load is added.
From this, can I deduce that:
a) The transformer is kaput (or, at least, on its way out)
b) There may be a borderline problem inside the monitor cabinet.
I've not got around to the multimeter test yet - I need to take the
mainboard out to access the underside, and that's not a task to be doing at
2:20am....
--
Cheers, Ade.
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