LG LST-5600A Service Manual page 20

(G) RS-232C check
YES
RS-232C port setup is OK?
(Baudrate, Parity, Data Bit, Stop Bit)
YES
IC204(10) is OK?(TxD signal)
Fig.09
YES
IC204(9) is OK?(RxD signal)
Fig.10
Fig.09 IC204(10) : TxD signal
Fig.10 IC204(9) : RxD signal
NO
NO
NO
3-11
Modify RS-232C port setup
Check IC101, IC204
Check IC101, IC204