Whirlpool WML55011HW Service Manual page 20

DIAGNOSTICS (Cont.)
Not Heating Troubleshooting Instruction
IMPORTANT: High-voltage is present at the magnetron and high-
voltage capacitor terminals. Avoid direct contact when power
is connected to these components to avoid serious injury or
possible death. Always be sure that the high-voltage capacitor is
discharged before accessing any of these components.
For a no-heat condition, refer to the following step-by-step
instructions:
1. Unplug microwave oven or disconnect power.
2. Discharge the high-voltage capacitor.
3. Disconnect the high-voltage transformer primary windings.
4. Attach the voltmeter leads to the high-voltage transformer
primary input wires.
5. Plug in microwave oven or reconnect power.
6. Close door and program the microwave oven to operate for
30 seconds.
7. Press START.
8. Check the input voltage at the high-voltage transformer
primary input wires. If the voltage is not close to the rating
voltage 120 ± 15 VAC, unplug microwave oven or disconnect
power. Check the circuitry as follows:
n Measure resistance of the fuse, micro-switches, and
thermostats. Replace any failed components. (Refer to
the wiring diagram.)
ACU Pin Voltage Matrix
Check for proper voltage by completing the following steps:
1. Unplug microwave oven or disconnect power.
2. Connect voltage measurement equipment to the terminals
listed below. (P1-3 and P2-1 are neutral.)
NOTE: For 50 V and over, the tolerance is ± 15 V. For 0 V, the tolerance is ± 3 V.
Abbreviations
HL - Hood Light, N - Neutral, CL - Cavity Light, HF - Hood Fan, L - Line Voltage, TT - Turntable Motor, NFS - Neutral for Switch
NOTE: When checking voltage readings on ACU, connect the Negative test lead of voltmeter to connector P1-3. Use the positive test
lead to probe connectors designated below.
Pin Name Wire Color
P1-1 (L) BLACK
P1-3 (N) BLUE
P2-1 (N/ BLUE AND
NFS) GREEN
P2-2 ORANGE
(Door)
P2-3 (N/ WHITE AND
NFS) BLACK
P4-1 (CL/ BLACK AND
CF) GREEN
P4-2 RED
(TTM)
2-6 n Low Profile Microwave Hood Combination
For Service Technician Use Only
MW Oven Plugged In—Sitting Idle—ACV Readings
Power Power On, Hood Fan
On, Door Door Open Motor—
Closed High
120 120 120
0 0 0
0 0 0
0 120 0
0 120 0
0 120 0
0 0 0
n Check for loose terminals. (Refer to the wiring diagram.)
Check all of the terminals on the main route from the
power supply to the high-voltage transformer.
n Check for loose or failed connectors on the PCBA
(P1, P2). If these check out OK, plug in microwave oven or
reconnect power.
n Check for ACU failure. Refer to "ACU Pin Voltage Matrix."
9. If the input voltage at the high-voltage transformer primary
input wires is close to the rating voltage 120 ± 15 VAC, unplug
microwave oven or disconnect power.
10. Check the power supply components. Refer to "Component
Tests."
n High-voltage transformer
n High-voltage capacitor
n High-voltage diode
11. If the power supply components check out OK, check the
connection between the magnetron and the high-voltage
transformer.
12. If all of the components check out OK, replace the
magnetron.
13. Reconnect the high-voltage transformer primary windings.
3. Plug in microwave oven or reconnect power, and confirm
voltage reading.
4. Unplug microwave oven or disconnect power.
Hood Fan Hood Fan Hood Fan
Motor— Motor— Motor—
Med-High Medium Low
N/A 120 120
N/A 0 0
N/A 0 0
N/A 0 0
N/A 0 0
N/A 0 0
N/A 0 0
MW Oven
Running—
ACV
Readings
Hood Hood Microwave
Light— Light— Oven Start
High Low
120 120 120
0 0 0
0 0 0
0 0 38
0 0 0
0 0 120
0 0 120