Streaky video can be one of two things...
Most likely, surface mount caps on the main board (ps2), causing video issues...very similar to whats happens with the Namco Classics series of Pcb's.
or, issues with your video chip (solder joints going cold, lifting pins, etc.)
If you don't surface mount solder, or aren't super handy with an iron, etc....Speedys is a division of Namco, and handles all their RMA repair, and has intimate knowledge of the 246/56 series boards, and their repair.
They have done several for the company I work for, and we have always been happy with them.