Re: screen flicker: probably not X related

On Monday 28 February 2005 04:37 am, Rick Miles wrote:

>
> I have to spend a day in Scoresby tomorrow and we lease a warehouse to a
> mob that make transformers and such. Maybe I can get something to use as a
> shield from them.
>
> Strange as it is. when I was googling on the other side I came across a
> link to a microsoft page that talked about such problems and suggested
> using a cookie sheet as a shield.
>
> I still have to try shifting things around a bit. Maybe switch PC positions
> Maybe get a cookie sheet that isn't teflon coated.............hmmm

What is inside the section of the PC nearest the monitor?....

I would almost make a bet that the wobble effect on the screen is caused by 
the changing magnetic field surrounding one of the PC's fans. These pesky 
little devices have permanent magnets in them, as well as having AC driven 
electromagnets. As the permanent magnet is spinning and the electromagnets 
fed with AC power from the fan's internal electronics both will have changing 
magnetic fields generated.... If the fan is not magnetically shielded 
properly this would make you CRT screen go crazy.

You could try unplugging the fans one at a time and power the computer up for 
a few seconds to see which fan is causing the problem.


I very much doubt it is going to be the power supply circuit itself as the 
transformers used in these operate at an extreemly high frequency, and 
usually have a 'shorted turn' type copper shield to keep their magnetic field 
under control. It could be the fan in the power supply though, these are 
usually a 12 Volt DC powered motor as described above.

Be very careful if you decide to open the power supply box up.... there are 
LETHAL voltages present inside that metal box!

Replacing a fan with a better quality unit is not usually an expensive 
exercise.


Good Luck,
Pip