CBM8032 - wobbly screen (The saga continues)

From: Adrian Vickers <avickers_at_solutionengineers.com>
Date: Tue Oct 9 04:27:43 2001

At 23:11 08/10/2001, you wrote:
> > Well, a screwdriver bit. It's one of those 1.5in long bits which go into a
> > handle, or drill.
>OK. Still a fair size piece of metal to move, and thus a fair size
>external field.


> > >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.
>It does sound as though you have transformer problems. You're making me
>curious enough to dig out one of my PETs and experiment with the
>transformer sometime just to see what I can detect.

I've got 4 PETs of various types here: The 2001 & 3016 have transformers
with steel bands around them - the 2001 screen is stable, the 3016 wobbles,
but almost imperceptably.

The 8032 and 8032-SK have a different type of transformer (without the
steel band), and wobble very noticably. It could have been a cost-cutting
exercise by CBM, with the result that the 8032 transformers are breaking
down more quickly.

> > No, not ridiculous (at least, I don't think so), but there is a noticable
> > increase when the monitor load is added.
>Interesting. So it might be PSU problems in the monitor. IIRC the monitor
>has a bridge rectifier input circuit. Check all 4 diodes and the
>soldering to them. If one is open you might have problems like this.

I shall give it a try tonight.

> > 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....
>Odd, I normally do delicate work like that at night. It's the one time
>you are not going to be disturbed while working on the system...

Hmm, I get tired & clumsy after about 1am - I start losing bits, forgetting
to make sure I'm earthed before touching chips & things. Far safer to
switch the 'phone off and do it straight after work...

Cheers, Ade.
Be where it's at, B-Racing!
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Received on Tue Oct 09 2001 - 04:27:43 BST

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