Hi John, 1st off microwaves are not a repair item for the untrained, they can and do kill even after being unplugged for months, so care is needed. if the unit is less than 3 years old
(warranty may still apply to parts) best get it to a local Panasonic dealer. the most likely problem is inverter failure, (the 4000v) power supply. For further help and advice contact me direct. info on microwave-repairs.co.uk
kindest regards
patrick, July 2009
