Diagnosis & Troubleshooting; Power Output Measurement; Failure Codes - Whirlpool MH9180XL Service Manual

DIAGNOSIS & TROUBLESHOOTING
The power output of the magnetron can be
measured using the following test. Before you
perform the test:
• Make sure that the microwave oven
cavity is clean and cool.
• Check the line voltage at the microwave
oven and note the reading.
1. Fill a glass beaker with 32 oz. (1000 ml) of
tap water.
2. Stir the water with a thermometer and record
the temperature. The temperature should
be between 50° and 75°F (10° and 24°C).
Likely Failure
Display
Condition
Flashing
Power Failure
colon ":"
Keyboard Failure Replace membrane switch. If problem persists, replace control system assembly.
-F2-
Humidity Sensor
-F3H-
Failure
Exhaust Fan
-F3T-
Thermostat Failure
1100W Inverter
-F7-
Failure
NOTE: If lights work, but cooling fan does not, 40W inverter may have failed.

POWER OUTPUT MEASUREMENT

FAILURE CODES

After a power failure, the colon ":" will be flashing. Press any key to end this indication.
The colon will then be steady when in standby.
Connect a new sensor to the board (at P5). If no failure code appears when starting sensor
function, replace old sensor. Otherwise, replace control system assembly.
1. Check that the oven temperature is not below 5°C (41°F) or above 60°C (140°F).
2. If problem persists, replace the control system assembly.
1. Unplug the oven for at least 40 seconds. Check to see if this solves the problem.
(Possible reason: Over temperature protection for the magnetron operated earlier.)
2. Check the resistance of the magnetron thermostat. It should be close to 0 ohms.
3. Check wiring to the 1100W inverter and control system.
4. Replace 1100W inverter.
5. If problem persists, replace control system assembly.
3. Place the beaker of water in the center of
the microwave oven cavity.
4. Operate the microwave oven on high power
for 1 minute.
5. Remove the beaker of water and stir it with
the thermometer for about 20 seconds.
6. Record the temperature of the water.
7. Subtract the temperature of the water you
recorded in step 2 from the water tempera-
ture in step 6. The normal rise in tempera-
ture range is shown in the following chart.
Voltage
(VAC Under Load)
120
108
Recommended Repair Procedure
6-1
Temperature Rise
°C °F
11 - 14 19.8 - 25.2
9.5 - 12.5 17.1 - 22.5