User manual

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Heater Shorted to Ground
Some components are switched on the neutral
side; therefore, it is possible to bypass the relay
and close the heater circuit by shorting it to
ground. If a heater shorts to ground, it will
energize any time the door is closed. This will
usually trip a GFCI but not a standard household
breaker. This problem will most likely cause the
cavity TCO to open. However, if a heater is
shorted to ground and the microwave is used,
either the 20-amp in-line fuse or the household
breaker will trip. If the sheath heater is shorted to
ground and Speedcook is used, the 12-amp fuse
on the sub PCB will trip.
Control Panel Test
The control panel circuits from the keys to the
main PCB can be verified by a continuity test.
1. Remove the control panel.
2. Disconnect connectors CN3 and CN4 from
the main PCB.
Terminal 11Terminal 11
Terminal 1Terminal 1
Terminal 11Terminal 11
Terminal 1Terminal 1
Connector
CN4
Connector
CN4
Connector
CN3
Connector
CN3
Main
PCB
Main
PCB
Control
Panel
Control
Panel
3. Using the chart, perform continuity tests for
the keys that are suspect. With the ohmmeter
leads connected to the appropriate terminals
on connector CN3 or CN4, press the key and
note the ohmmeter reading.
• key not pressed - infinite resistance should
be measured
• key pressed - continuity should be
measured
Note: Ohmmeter must be set at high scale.
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Low Voltage Transformer Test
To perform a low voltage transformer test:
Verify 120 VAC is present at CN1 on main PCB
across the white and black wires. If 120 VAC is
not present, suspect a faulty main PCB. If
120 VAC is present, use the following chart to
check the voltage output of the low-voltage
transformer.
If the voltage output or resistance is not correct,
replace the low voltage transformer.
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