Sunday, February 28, 2016

PANASONIC NN-SE992S - NN-SD982S - NN-ST962S – Inverter power supply working – Testing magnetron – Measuring the microwave output – Energy leakage test – Troubleshooting – Microwave oven repair and service

PANASONIC NN-SE992S - NN-SD982S - NN-ST962S

Inverter power supply circuit working
The Inverter Power Supply circuit powered from the line voltage, 120V 60Hz AC input supplies 4,000V DC to the magnetron tube, and functions in place of the H.V. transformer, the H.V. capacitor and H.V. diode.
1. The AC input voltage 120V 60Hz is rectified to DC voltage immediately.
2. DC voltage will be supplied to the switching devices called IGBT. These devices are switched ON-OFF by the 20 to 40 kHz PWM (pulse width modulation) signal from the microcomputer in the DPC.
3. This drives the High voltage transformer to increase voltage up to 2,000V AC.
4. Then the half-wave doubler voltage rectifier circuit, consisting of the H.V. diodes and capacitors, generates the necessary 4,000V DC needed for the magnetron.
5. Output power of the magnetron tube is always monitored by the signal output from the current transformer built into the inverter circuit.
6. This signal is fed back to the microcomputer in the DPC to determine operating conditions and output necessary to control PWM signal to the Inverter Power Supply for control of the output power.
COMPONENT TEST
Primary, Secondary Interlock Switch & Power Relay RY1
1. Unplug lead connectors to Power Relay RY1 and verify open circuit of the Power Relay RY1 1-2 terminals.
2. Unplug lead connectors to Primary Interlock Switch and Secondary Interlock Switch.
3. Test the continuity of switches at door opened and closed positions with ohm meter (low scale). Normal continuity readings should be as follows.
Primary Interlock Switch 0Ω (Close) Ω(Open)
Secondary Interlock Switch 0Ω (Close) Ω(Open)
Power Relay RY1 Ω (Open) Ω(Open)
Monitor Switch
1. Unplug lead wires from Inverter Power Supply (U) primary
terminals.
2. Connect test probes of ohm meter to the disconnected leads that were connected to Inverter Power Supply (U).
3. Test the continuity of Monitor Switch with door opened and closed positions using lowest scale of the ohm meter. Normal continuity readings should be as follows.
Door Opened Door Closed
0Ω (Close) Ω (Open)
Magnetron
Continuity checks can only indicate an open filament or a shorted magnetron. To diagnose for an open filament or shorted magnetron.
1. Isolate magnetron from the circuit by disconnecting the
leads.
2. A continuity check across magnetron filament terminals should indicate one ohm or less.
3. A continuity check between each filament terminal and magnetron case should read open.

Key board membrane (Membrane switch assembly)
Check continuity between switch terminals, by tapping an appropriate pad on the key board. The contacts assignment of the respective pads on the key board is as shown in digital programmer circuit.
Inverter power supply 
DO NOT try to REPAIR H.V. Inverter power supply (U).
Replace complete H.V. Inverter(U) Unit.

WARNING: HIGH VOLTAGE
Test if failure codes H95, H97 or H98 appear when performing the following procedure. It is recommended to use an AC line input current ammeter for testing.
Test 1
1. With the oven unit’s AC power supply cord is unplugged from the wall outlet, unplug the 2 pin H.V. connector CN703 from the magnetron tube.
2. Place 1 liter of water load into oven cavity.
3. Plug in the oven’s AC power supply cord into outlet.
4. Program DPC.
a. Press Timer/Clock button twice.
b. Press Start button once.
c. Press Power Level button once.
5. Program oven at High power for 1 minute and press [Start] button.
a. After approximately 23 seconds, oven stops operating.
b. During oven operation, the input current is approximately 0.5 to 1A. If both a and b are OK, proceed to test 2.
Unplug CN703 0.5 to 1A Oven stops in 23 seconds after started.
Test 2
Continued from Test 1
1. Unplug the oven’s AC power supply cord from outlet.
2. Unplug 3 pin connector CN701. CN703 remains unplugged.
3. Plug in the oven’s AC power supply cord into outlet.
4. Program DPC.
a. Press Timer/Clock button twice.
b. Press Start button once.
c. Press Power Level button once.
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.
1200W Min. 18.5°F(10.3°C)
MEASURING MICROWAVE ENERGY LEAKAGE
Equipment
# Electromagnatic radiation monitor
# Glass thermometer 212°F or 100°C
# 600cc glass beaker
Procedure for measuring radiation leakage
Note before measuring:
# Do not exceed meter full scale deflection. Leakage monitor should initially be set to the highest scale.
# To prevent false readings, the test probe should be held by the grip portion of the handle only and moved along the shaded area in Figure no faster than 1 inch/sec (2.5cm/sec).
# Leakage with the outer panel removed: less than 5mW/cm2.
# Leakage for a fully assembled oven with door normally closed: less than 2mW/cm 2.
# Leakage for a fully assembled oven [Before the latch switch (primary) is interrupted] while pulling the door: less than 2mW/cm 2.
1. Pour 275 ± 15cc (9ozss± 1/2oz) of 20°C ± 5°C (68° ± 9°F) water in a beaker which is graduated to 600cc, and place in the center of the oven.
2. Set the radiation monitor to 2450MHz and use it following the manufacturer´s recommended test procedure to assure correct results.
3. When measuring the leakage, always use the 2 inch (5cm) spacer supplied with the probe.
4. Tap the start button or set the timer and with the magnetron oscillating, measure the leakage by holding the probe perpendicular to the surface being measured.
TROUBLESHOOTING
H97 & H98 error code display
If 3 times H97 or 2 times H98 exist, microwave oven can not be used any more, even if the defective parts already be replaced & un-plug and plug-in again.
How to reset for the service:
Please take the following steps
1. Plug-in oven.
2. Press Stop/Reset button once.
3. Open the door.
4. Keep pressing Start button for more than 2 seconds until buzzer beeps.
5. Press Stop/Reset button three times, oven will show the total usage time of magnetron.
6. Press Power Level button once, oven will show the total number of occurrence of H97 & H98.
7. Keep pressing Start button for more than 2 seconds (until buzzer beeps) to reset.
8. While finish resetting, one beeps, and show “end”.
9. Press Stop/Reset to return to initial stage.
Magnetron usage time display
Oven has magnetron usage time display function but it will not be activated in normal operation mode.
To show magnetron usage time result, please take the following steps:
1. Plug-in oven.
2. Press Stop/Reset button once.
3. Open the door.
4. Keep pressing Start button for more than 2 seconds until buzzer beeps.
5. Press Stop/Reset button three times, oven will show the total usage time of magnetron.
(note1:the magnetron usage time is kept in L.S.I. memory.)
(note2:Magnetron usage time display is in hours.)
NOTE:
To delete the recorder of L.S.I. memory.
a. Press Start button for more than 2 seconds until buzzer beeps.
b. While finish deleting, one beeps and show “end”.
c. Press Stop/Reset to return to initial stage.