Manuel, I found the following symptom listed on Ray Carlsen's website: UF4 906109-04 (6567) VIC (has heat sink attached) on CPU board. Blank white screen, no border. Sometimes will produce garbage or "checkerboard" screen, or screen that lacks contrast. If screen is blank or garbled from bad VIC, "blind" disk commands from keyboard -may- still work.This is the only thing he lists for SX-64's for a WHITE screen. You can read the entire page here:
http://personalpages.tds.net/~rcarlsen/cbm/sx64.txt Hope this helps!-Andrew