Whirlpool WML55011HW Service Manual page 29

Components
Hood Exhaust Fan Motor
HF NTC Thermistor
AC Line Filter Board
Thermostats
Cavity Thermostats
Magnetron Thermostat
Open Door Switch
Switch
POWER OUTPUT MEASUREMENT
The power output of the magnetron can be measured using the following "Voltage Measurement at Power Source" and "Output Test"
sections. Before you perform the test:
n Make sure that the oven cavity is cool and clean.
n Check the line voltage at the wall outlet while microwave oven is operating. See the "Voltage Measurement at Power Source"
section.
Tools Needed
n 2-cup measuring cup
n Thermometer
n Voltmeter/ohmmeter
Voltage Measurement at Power Source
1. Fill the measuring cup with 2 cups (500 mL) of tap water.
2. Place in the center of the microwave oven cavity.
3. Operate the microwave oven on high power for 1 minute.
4. While the microwave oven is operating, measure the
line voltage at the power source. See "Measure Voltage"
illustration.
5. Verify the voltage is constant during microwave oven
operation. If voltage drops below 108 V, contact a qualified
electrician to check your electrical supply.
6. Make note of the voltage while the microwave oven is
running and proceed to the output test.
For Service Technician Use Only
Test/Results
1. Unplug microwave oven or disconnect power.
2. Remove wire leads.
3. Measure resistance:
n High Speed—Normal: Red (RD) and Blue (BU) wires: 70 to 170 ohms (approximate);
Blue (BU) and Black (BK) wires: 20 to 100 ohms (approximate)
n Middle Speed-Normal: Grey (GY) and Blue (BU) wires: 50 to 130 (approximate)
n Low Speed—Normal: White (WH) and Blue (BU) wires: 60 to 160 ohms (approximate);
Blue (BU) and White (WH) wires: 80 to 150 ohms (approximate)
1. If "NTC SHORT, CALL FOR SERVICE" or "NTC OPEN, CALL FOR SERVICE" scrolls on display,
unplug microwave oven or disconnect power.
2. Measure hood thermistor:
n Normal: 10 k ohms +/-5% at 77°F (25°C)
1. Unplug microwave oven or disconnect power.
2. Remove wire leads.
3. Measure resistance:
n Normal: L-IN to L-OUT (coil): Less than 1 ohm; N-IN to N-OUT (coil): Less than 1 ohm
NOTE: Refer to "Parts Layout" for opening and closing temperatures.
1. Unplug microwave oven or disconnect power.
2. Remove wire leads.
3. Measure continuity:
n Normal: Continuity
1. Unplug microwave oven or disconnect power.
2. Remove wire leads.
3. Make sure the switch is pressed
4. Measure resistance:
n Normal: >1M ohm
n Abnormal: <5 ohm
COMPONENT TESTING (Cont.)
Measure Voltage
A
B
C
A. House power supply wall outlet
B. Voltmeter/ohmmeter test leads
C. Microwave oven plug
Low Profile Microwave Hood Combination n 3-7