Mitsubishi Electric MXZ-SM72TAM-U1 Service Manual page 55

4220 (U9): Voltage shortage/Overvoltage/PAM error/L1 open phase/
Diagnosis of failure
Continued from the previous page.
7, 8
Check the power supply voltage on the terminal block
of the outdoor unit.
Is the power supply normal?
Check the bus voltage read by the microprocessor with
an operation of SW1 on the outdoor multi controller
circuit board.
Check the bus voltage at the test points listed
below on the outdoor power circuit board using a
multimeter.
Test points: CNDC 1-3 pin
Is the bus voltage normal?
OCH800A_55
Primary current sensor error/Power synchronization sig-
nal error
No
Yes
No
Yes
Check the power supply facility.
The bus voltage can be displayed by an operation of SW1
on the outdoor multi controller circuit board.
SW1 Setting Display on LED1,2
Unit
ON
0–9999 V
OFF
1 2 3 4 5 6 7 8
Check the resistor connected to 52C relay and
reactor.
Replace it if the resistor is broken.
Replace the outdoor power circuit board if the
resistor is not broken.
Operate the unit and check if the problem occurs
again.
The black square (■) indicates a switch position.
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