27 Sep
2001
27 Sep
'01
10:01 p.m.
At 02:17 28/09/2001, Bill Dawson wrote:
-> Since I left the big cap in place, it can only be
the transformer
-> which is causing the wobble - can't it?
->
-> I genuinely don't know. That's the only part I've swapped in the
-> new 8032.
-> Could a flakey transformer be making the screen wobble? How do
-> transformers go flakey anyway, if indeed they *can* co flakey?
Well, actually I think the transformer is the cause of the problem, but not
in the way you are thinking. You may have an problem with the magnetic
field of the transformer being coupled to the monitor, either via the yoke
or directly to the CRT. Does the problem lessen as the distance between the
transformer and the monitor is increased?
I don't know - to try that I'd have to disassemble the whole thing again :(
The earth wires are a bit too short to make testing that easy.
See the photos of the Commodore Educator 64, Model 4064
at
http://www.swtpc.com/commodor.htm . I remember the general position of the
power transformer is similar to the Pets. Note the shielding of the
transformer in the photos. This was used to prevent the problem which you
are describing, and if this shielding is removed the wobble will occur. Try
placing a shaded pole motor or large transformer anywhere near the sides or
back of a modern monitor and you'll see the same wobbling effect.
Interestingly, the US transformer is of a different design to the UK one;
I'm assuming the primary windings are inside the secondary, and there's a
broad metal band strapped around the whole thing. The UK transformer has
the primary & secondary windings next to each other, and there's no
shielding at all. If I fabricate a box, I assume it'll have to be earthed,
and surround the whole transformer? Also, will any metal do, or does it
need to be ferric?
--
Cheers, Ade.
Be where it's at, B-Racing!
http://b-racing.co.uk