Panasonic NN-K593MF Service Manual

Unlike many other appliances, the microwave oven is a highvoltage, high current device. It is free from danger in ordinaryuse, though extreme care should be taken during repair.CautionServicemen should remove their watches wheneverworking close to or replacing the magnetron.4.1. Check the groundingDo not operate on a two wire extension cord. The microwaveoven is designed to be grounded when used. It is imperative,therefore, to ensure the appliance is properly grounded beforebeginning repair work.4.2. Inverter warningsDANGER, HIGH VOLTAGE AND HIGH TEMPERATURE(HOT/LINE) OF THE INVERTER POWER SUPPLY (U)This high voltage inverter power supply handles very highvoltage and current for the magnetron tube. Though it isfree from danger in ordinary use, extreme care should betaken during repair.The aluminum heat sink is also energized with high voltage(HOT), so do not touch when the AC input terminals areenergized. The power devices Collector is directlyconnected to the aluminum heat sink.The aluminum heat sink may be HOT due to heat energy,therefore, extreme care should be taken during servicing.H.V. Inverter warningWARNING FOR INVERTER POWER SUPPLY (U)GROUNDINGCheck the high voltage inverter power supply circuitgrounding. The high voltage inverter power supply circuitboard must have a proper chassis ground, the invertergrounding bracket must be connected to the chassis. If theinverter board is not grounded it will expose the user to veryhigh voltages and cause extreme DANGER! Be sure thatthe inverter circuit is properly grounded via the inverterearth bracket.Grounding of the inverter circuit boardWARNING! DISCHARGE THE HIGH VOLATGECAPACITORSFor about 30 seconds after the oven is turned off, anelectric charge remains in the high voltage capacitors in theinverter power supply circuit board.When replacing or checking parts, remove the power plugfrom the outlet and short the inverter output terminal of themagnetron filament terminals to the chassis ground with aninsulated handle screwdriver to discharge. Please be sureto touch the chassis ground side first and then short to theoutput terminals.Discharging the high voltage capacitorsWARNINGThere is high voltage present with high current capabilitiesin the circuits of the primary and secondary windings, chokecoil and heat sink of the inverter. It is extremely dangerousto work on or near these circuits with the oven energized.DO NOT measure the voltage in the high voltage circuitincluding the filament voltage of the magnetron.WARNINGNever touch any circuit wiring with your hand or with aninsulated tool during operation.4 CAUTIONS TO BE OBSERVED WHENTROUBLESHOOTING8NN-S453WF