Mitsubishi Electric PUHY-HP72 Service Handbook page 245

[8-10 Control Circuit ]
2) TNU
Check the voltage at the indoor/outdoor
transmission terminal block (TB3) of outdoor unit.
Check the voltage at TB3 after removing
transmission line from TB3.
Check whether the male connector is connected to the
female power supply connector (CN40).
NO
Check voltage of terminal block for centralized control (TB7).
Check voltage of TB7 by removing transmission line from TB7.
Check the voltage across pins 3 and 4 of CNPW on the control board.
Check the voltage across pins 1 and 2 of CNPW on the control board.
Check the voltage across pins 1 and 2 of CN600 on the control board.
Check the wiring between the control board and
power-supply board, and also check connectors
CN600 and CNDC for proper connections.
Check the wiring between the noise filter board and
power-supply board, and also check connectors
CN12 and CN100 for proper connections.
Check fuse F001 on the noise filter board.
48
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YES
24-30 VDC
NO
YES
24-30 VDC
NO
Connected
YES
YES
24-30 VDC
NO
NO
YES
24-30 VDC
NO
YES
24-30 VDC
NO
YES
24-30 VDC
NO
NO
YES
8-12 VDC
NO
YES
Any problems with wiring or
loose connectors?
NO
YES
Any problems with wiring or
loose connectors?
NO
YES
Fuse F001 is blown.
NO
A
Check whether the transmission line is disconnected,
check for contact failure, and repair the problem.
Check if the indoor/outdoor transmission line is
not short-circuited, and repair the problem.
Check the wiring between the control board and
power-supply board, and also check connectors CNPW,
CNPS, CN202, and CNINT for proper connections.
YES
Fix the wiring and connector
Is there a wiring
error or a connector
disconnection.
disconnection?
Check for shorted transmission
line or power feed collision for
centralized control.
Replace the control board.
Check the wiring between the control board and
power-supply board, and also check connectors CNPW,
CNPS, CN202, and CNINT for proper connections.
YES
Any problems
Correct wiring problems, and
with wiring or loose
tighten loose connectors.
connectors?
NO
Check the voltage across pins 4-1 of CNPS on the control board.
YES
Replace the power-supply board.
3.25-3.35 VDC
Replace the control board.
Correct wiring problems, and tighten loose connectors.
Correct wiring problems, and tighten loose connectors.
Disconnect CN12 on the noise filter board,
replace F001, and turn on the power supply.
YES
Fuse F001
Replace the noise filter.
is blown.
NO
Replace the power-supply board.
B
HWE18240_GB