you have to go into the service mode to change it. to get into service mode, use remote control, press menu 7,9,3,5. look for 'Burn In' option and switch it off using arrow keys on remote. then switch tv to standby and back on and it should be fine. if it's not, then it's dry joints and you need an engineer. ignore everything else in service menu cause you can seriously damage tv by changing wrong thing.
james, March 2010