LG DP122NU Service Manual page 19

When you plug power cord and turn the unit on, LED light won't turn red, the unit won't
read disc nornally.
1-5. Please check main board IC U4 singal and its peripheral circuit.
1) Please check if output voltage 5 V from U4 pin8, pin19 is normal.
If output voltage 5 V is not normal, please check 5 V power circuit of main board.
2) Please check every singal connected between IC U4 and IC U1, especially including F+, F-, T+, T-,
SP+, SP-, SL+, SL- signal to drive MD.
If F+, F-, T+, T-, SP+, SP-, SL+, SL- signal is not normally output, please check if U4 is in failure.
ONE POINT REPAIR GUIDE
U4
< Main Board Top View >
U1
3-6