Board repair is rare so you have to find a service manual then follow the charts, change the boards until it's fixed.
More at http://www.shopjimmy.com/tv-repair-tips
I have a PROSCAN 50 INCH TV (PLDED5066A-E) (sn:A1305096070000235 ) Turns on and runs good for about a min or two then goes black. Can see picture with a flashlight. turn it of and back on the same thing happens.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic