I own a Philips plasma panel,model number 42PF9966/79

I own a Philips plasma panel,model number 42 PF9966/79. Approximately 30 mins after warm up an effect like someone is using a green spray paint can, works from the outside of the picture towards the centre until no picture is viewable..changing channels and returning alleviates the problem for a minute or so..then the cycle repeats itself but with shorter viewing times until this is no longer possible.My tech says probably have to change the guts of the TV beginning with the 'Y buffer boards' until problem is solved....Any thoughts would be greatly appreciated while I still have hair!