LG 28cz10rx fault

[zoodemon]

Hi, i have a 2 year old Lg ri-28cz10rx tv which is out of warranty has started behaving erratically. The picture becomes momentarily brighter, and then darkens until black. It occasionally comes back on, with a reversal of the previous process. Dark to light in a steady action. Sound is not affected, just picture. I have checked all leads, and sources, but the tv is the problem. I have brought up the on screen display whilst the picture darkened, to see if the picture components/settings were changing but they remained static. Do you know what the problem is, and can it be easily/cheaply repaired? thanks