Ma Remote Controller Problems; The Lcd Does Not Light Up - Mitsubishi Electric HP120TNU-A Service Handbook

[8-1 MA Remote Controller Problems ]

8 Troubleshooting Based on Observed Symptoms
8-1

MA Remote Controller Problems

8-1-1

The LCD Does Not Light Up.

1. Phenomena
Even if the operation button on the remote controller is pressed, the display remains unlit and the unit does not start running.
(Power indicator ( ) is unlit and no lines appear on the remote controller.)
2. Cause
1) The power is not supplied to the indoor unit.
The main power of the indoor unit is not on.
The connector on the indoor unit board has come off.
The fuse on the indoor unit board has melted.
Transformer failure and disconnected wire of the indoor unit.
2) Incorrect wiring for the MA remote controller
Disconnected wire for the MA remote controller or disconnected line to the terminal block.
Short-circuited MA remote controller wiring
Incorrect wiring of the MA remote controller cables
Incorrect connection of the MA remote wiring to the terminal block for transmission line (TB5) on the indoor unit
Wiring mixup between the MA remote controller cable and 220-240 VAC power supply cable
Reversed connection of the wire for the MA remote controller and the M-NET transmission line on the indoor unit
3) The number of the MA remote controllers that are connected to an indoor unit exceeds the allowable range (2 units).
4) The length or the diameter of the wire for the MA remote controller are out of specification.
5) Short circuit of the wire for the remote display output of the outdoor unit or reversed polarity connection of the relay.
6) The indoor unit board failure
7) MA remote controller failure
3. Check method and remedy
1) Check the voltage at the MA remote controller terminals.
If the voltage is between DC 9 and 12V, the remote controller is a failure.
If no voltage is applied, check the causes 1) and 3) and if the cause is found, correct it.
If no cause is found, refer to 2).
2) Disconnect the remote controller cable from TB15 (MA remote controller terminal) on the indoor unit, and check the voltage
across the terminals on TB15.
If the voltage is between DC 9 and 12 V, check the causes 2) and 4) and if the cause is found, correct it.
If no voltage is applied, check the cause 1) and if the cause is found, correct it.
If no cause is found, check the wire for the remote display output (relay polarity).
If no further cause is found, replace the indoor unit board.
HWE18220_GB
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