Sony 36 xbr tv goes on & off.

My trusty old wega 36" xbr tv is giving me trouble after 13 years.  When turned on, the picture shuts off, then on, then off and so continually, but the sound stays on, and when the picture does flash on the screen, it's a great picture.  I know there are no simple fixes, but is the tube going, or could this be a power issue only ?????