Monitor Goes Black or wont turn on

Hi all
i have 2 sony hs75p one of them when you turn it on after a while it goes black or sometimes wont turn on at all. the lamp and inverter board is good because i switch the inverner board on my monitors and it works but the same monitor goes black after a while (it works for a while ) i'm thinking about the power board because it has two seprate board for power and inverter any body has any experiance with power board or how can i check it? i look at the board to see if there is any bad capaciator or bad join but it looks fine.