Wednesday, January 20, 2016

PANASONIC Microwave oven NN-GD576 - NN-GT546 - NN-SD556 - NN-ST556 – Measurement and Adjustment procedure - Microwave Oven Repair and service

PANASONIC NN-GD576 - NN-GT546 - NN-SD556 - NN-ST556

CAUTIONS TO BE OBSERVED WHEN TROUBLESHOOTING
Unlike many other appliances, the microwave oven is a high voltage, high current device. It is free from danger in ordinary use, though extreme care should be taken during repair.
Caution
Servicemen should remove their watches whenever working close to or replacing the magnetron.
Check the grounding
Do not operate on a two wire extension cord. The microwave oven is designed to be grounded when used. It is imperative, therefore, to ensure the appliance is properly grounded before beginning repair work.
Inverter warnings
DANGER, HIGH VOLTAGE AND HIGH TEMPERATURE (HOT/LINE) OF THE INVERTER POWER SUPPLY
The high voltage inverter power supply handles very high voltage and current for the magnetron tube. Though it is free from danger in ordinary use, extreme care should be taken during repair.
The aluminum heat sink is also energized with high voltage (HOT), do not touch when the AC input terminals are energized. The power device Collector is directly connected to the aluminum heat sink. The aluminum heat sink may be HOT due to heat energy, therefore, extreme care should be taken during servicing.
WARNING FOR INVERTER POWER SUPPLY GROUNDING
Check the high voltage inverter power supply circuit grounding. The high voltage inverter power supply circuit board must have a proper chassis ground. The inverter grounding bracket must be connected to the chassis. If the inverter board is not grounded it will expose the user to very high voltages and cause extreme DANGER! Be sure that the inverter circuit is properly grounded via the inverter earth bracket.
WARNING DISCHARGE THE HIGH VOLATGE CAPACITORS
For about 30 seconds after the oven is turned off, an electric charge remains in the high voltage capacitors in the inverter power supply circuit board. When replacing or checking parts, remove the power plug from the outlet and short the inverter output terminal of the magnetron filament terminals to the chassis ground with an insulated handle screwdriver to discharge. Please be sure to touch the chassis ground side first and then short to the output terminals.
WARNING
There is high voltage present with high current capabilities in the circuits of the primary and secondary windings, choke coil and heat sink of the inverter. It is extremely dangerous to work on or near these circuits with the oven energized.
DO NOT measure the voltage in the high voltage circuit including the filament voltage of the magnetron.
WARNING
Never touch any circuit wiring with your hand or with an insulated tool during operation
Part replacement.
When any part or component is to be replaced, always ensure that the power cord is removed from the wall outlet.
When the 10A fuse is blown due to the operation of the short switch:
WARNING
When the 10A 250V fuse is blown due to the operation of the interlock monitor switch, replace all of the components (primary latch switch, secondary latch switch, short switch and power relay B (RY1)).
1. This is mandatory. Refer to “adjustments and measurements” for the location of these switches.
2. When replacing the fuse, confirm that it has the appropriate rating for these models.
3. When replacing faulty switches, be sure the mounting tabs are not bent, broken or deficient in their ability to hold the switches.
Avoid inserting nails, wire etc. through any holes in the unit during operation.
Never insert a wire, nail or any other metal object through the lamp holes on the cavity or any holes or gaps, because such objects may work as an antenna and cause microwave leakage.
Confirm after repair
1. After repair or replacement of parts, make sure that the screws of the oven, etc. are neither loose nor missing. Microwaves might leak if screws are not properly tightened.
2. Make sure that all electrical connections are tight before inserting the plug into the wall outlet.
3. Check for microwave energy leakage. (Refer to procedure for measuring microwave energy leakage).
CAUTION MICROWAVE RADIATION
USE CAUTION NOT TO BECOME EXPOSED TO RADIATION FROM THE MICROWAVE MAGNETRON OR OTHER PARTS CONDUCTING MICROWAVE ENERGY
IMPORTANT NOTICE
The following components have potentials above 2000V while the appliance is operated.
# Magnetron
# High voltage transformer (Located on inverter.
# High voltage diodes (Located on inverter).
# High voltage capacitors (Located on inverter)
Pay special attention to these areas. When the appliance is operated with the door hinges or magnetron installed incorrectly, the microwave leakage can exceed more than 5mW/cm2. After repair or exchange, it is very important to check if the magnetron and the door hinges are correctly installed.
Sharp edges
Caution
Please use caution when unpacking, installing or moving the unit, as some exposed edges may be sharp to the touch and cause injury if not handled with care.
MEASUREMENTS AND ADJUSTMENTS
Adjustment of primary latch switch, secondary latch switch and short switch.
1. Mount the Primary latch switch, the secondary latch switch and the short switch to the door hook assembly as shown in ILL.
NOTE:
No specific individual adjustments during installation of the Primary latch switch, Secondary latch switch or Short switch to the door hook are required.
2. When mounting the door hook assembly to the oven assembly, adjust the door hook assembly by moving it in the direction of the arrows in the illustration, so that the oven door will not have any play in it. Check for play in the door by pulling the door assembly. Make sure that the latch keys move smoothly after adjustment is completed. Completely tighten the screws holding the door hook assembly to the oven assembly.
3. Reconnect the short switch and check the continuity of the monitor circuit and all latch switches again by following the component test procedures.
Measurement of microwave
output
The output power of the magnetron can be determined by performing IEC standard test procedures. However,due to the complexity of IEC test procedures, it is recommended to test the magnetron using the simple method outlined below.
Necessary Equipment:
*1 liter beaker *Glass thermometer
*Wrist watch or stopwatch
NOTE:
Check the line voltage under load.Low voltage will lower the magnetron output. Take the temperature readings and heating time as accurately as possible.
1. Fill the beaker with exactly one liter of tap water.Stir the water using the thermometer and record the water’s temperature. (recorded as T1).
2. Place the beaker on the center of glass tray. Set the oven for High power and heat it for exactly one minute.
3. Stir the water again and read the temperature of the water. (recorded as T2).
4. The normal temperature rise at High power level for each model, is as shown in table.
RATED OUTPUT
TEMPERATURE RISE
1000W
Min. 8.6°C
1100W
Min. 9.4°C