LG GWA-4164B Service Manual page 82

LS Media Recognition Fail:
LS CD, DVD
Check the Cleanness of Media.
YES
Check Encoder IC Power.
YES
Check the OFG Signal.
YES
Check P/U Read Power
4.5~5.5mW.
YES
Check the RXD/RFS_INT Signal
On Recognizing LS Media..
OK
86
NO
Change the Media.
NO
Check 3pin FFC and Q501.
NO
Check Enc Assy's Alignment and
Grease on it.
NO
Go to 'LD CHECK'.
NO
Replace IC501, 502.