Picture keeps going off anf on, but sti...

Unfortunately that's an indication of the crt going bad in a Sony.
You can turn the G2 voltage down on the flyback or have a tech rejuvenate the picture tube but either of these are only a temporary fix..
The flyback is the rather large transformer with a red (anode) wire coming from it and attaching to the crt. (looks like a suction cup).
There are two adjustments on the back of the FBT, one is screen (or G2) the other is focus. With the unit on turn the G2 counter clockwise just a little and the picture will get slightly less bright. That should stop the picture from blinking out - or doing so as often. But again, it's only temporary!
Good thing Santa's almost here... :)
Bill