Osbourne Executive help

I have an Osbourne Executive that is in fairly decent shape and for the most part works fine. There's no burn-in on the CRT and both floppies work great, but there seems to be a problem with the power supply or the video system. The system boots fine, but once it has booted, the image on the screen begins to jump or shimmer, and you can hear the fan on the rear of the machine appear to change speeds, as if there was a power fluctuation. I would really like to find out what's wrong with this machine, and repair it if possible, and am hesitant to run it the way it is. Any help would be greatly appreciated. Thanks. Jeff jeffh(a)eleventh.com -- --------------------------------------------------------------------- Sent from an Amiga 3000..the computer for the creative mind! --------------------------------------------------------------------- Collector of classic home computers: Amiga 1000, Atari 800, 800XL, Mega-ST/2 and XE System, Commodore C-128D, Plus/4 and VIC-20, IBM 5155, Kaypro 2X, Osbourne Executive Radofin Aquarius, Sinclair ZX-81, TI-99/4A, Timex-Sinclair 1000, TRS-80 Color Computer-3 and Model 4, plus Atari Superpong and 2600VCS game consoles.