Phil Allison wrote:
"Tim Worthington"

I'm thinking about putting a posister, the coil and a degauss
button in series with the 240v mains available inside the box.


** You need a bit more than that - usually a hefty relay is used to
engage the posistor circuit with a timer to hold it on for 5 seconds or
so.
The button just initiates the timing cycle.

I have Sanyo TVs built over 20 years ago that use nothing but a
posistor in series with the degaussing coil.



** TVs are nearly all like that.

However, the OP has a portable monitor that may need to be de-gaussed
whenever it is moved about.

Hence the need for a "de-gauss" button.





.............. Phil