Sinclair SCV-750EB Service Manual page 77

For SCV-750EB, SCV-1400EB and SCV-1800EB:
Communication wires X Y E have short
circuited, disconnected or are
Communication wires X Y E are not
connected in a daisy chain
Wires between outdoor main PCB and
electric control box communication
terminals block are loose
Interference from high voltage (220V or
Communication wires are close to a source
of electromagnetic radiation such as
transformer or strong fluorescent lamp
Damaged control box communication
The length of communication wire is over
Replace main PCB or user interface
Notes:
1. Measure the resistance among X, Y and E. The normal resistance between X and Y is 120Ω, between X and E is infinite, between Y and E is infinite.
Communication wiring has polarity. Ensure that the P wire is connected to P terminals and the Q wire is connected to Q terminals.
2. Check whether the communication wires X, Y and E between units have disconnected or are misconnected.
E2
misconnected 1
No
No
No
higher) wires
No
No
terminals block
No
1200m
No
Yes
Reconnect the communication wires
Connect the communication wires in a
Yes
daisy chain
Yes
Ensure the wires are connected properly
Ensure the communication wires and high
Yes
voltage wires are separated
Remove the source of interference, or add
Yes
additional shielding to the communication
Replacing electric control box
Yes
communication terminals block resolves
Reduce the wire length to less than
Yes
1200mm or strengthen the signal
wires
the error
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