🚀 go-pugleaf

My sister is having problems with the monitor integrated into her Performa
5200CD. The image quality is excellent when the computer is first switched
on but after 25 minutes the image starts to ripple and then suddenly
reduces in size before the monitor goes blank. After I shut down the
computer and restart the same thing happens, again after 25 minutes. There
is no colour distortion.
My guess is that it is a component level failure (probably a capacitor).
I'd rather not take it to an Apple dealer to have it serviced since they
will charge exorbitent amount and won't attempt to find the cheapest
solution. I thought a local electrical service centre that handles
computer monitors would be the best way to proceed.
Any enlightenment as to the cause of this problem, feasibility of repair,
and  the best repair solution would be greatly appreciated.

Thanks in advance,

Steven