Peugeot 307 help help help

i guys im having trouble with my trip computer after 30 mins it starts to go blur and then lose letters n numbers???? iv had it plugged into the computer diagnostic thing...it came back ok no faults at all iv had a good working trip display put in my car and that one did the same??? theres no bad earth thats all been checked?? someone said i could have the wrong bulbs in?? maybe there to high a watt for the display??? so waht is the correct watt bulb for the display???