Service
Chapter 340
signal. Check the following levels of the square wave with an oscilloscope.
• At the black/white wire: -0.05 ± 0.05 Vdc (top of square wave).
• At the brown/white wire: -9Vdc (bottom of square wave).
If the levels are incorrect, then the power meter or sensor cable is at fault. Refer to
the power meter service manual for troubleshooting information.
If the levels are correct then the Power Sensor is at fault. Continue by
troubleshooting the A1 Bulkhead Assembly.
Troubleshooting - Power Sensors
The most common cause of Power Sensor failure is the application of power levels
beyond the specified tolerance. The second most common cause of failure is
applying torque to the body of the Power Sensor. Either of these common causes
damages the bulkhead cartridge unit (which holds the thermocouples/diodes). If this
happens, the fault causes a short or an open between the two gold wires.
A1 Bulkhead (Thermocouple Sensors)
CAUTION Disconnect the gold wires from the A2 assembly before measuring the resistance.
Be extremely careful when measuring across the gold wires. They are delicate and
can be damaged easily.
Step 1. Disconnect all cables from the Power Sensor.
Step 2. Remove the clamp holding the two gold wires.
Step 3. Resistance measured between the two gold wires from the A1 Bulkhead Assembly
is listed in Figure 3-1.
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