This is a well known problem and occurs on all 42PD models once they reach 12 months old and above.
It is invariably Resistor R003 or R005 on the main power supply board. These are 10 ohm 5 Watt resistors (one is a fused resistor at 5A) but replacing them with 10 ohm 7-10 watt devices usually fixes the problem.
Dave
April 2009