LG CM4550 Service Manual page 28

NO OPERATION OF MD
When no sound output in the CD function, you can not listen to music reading data
from a CD disc if the pickup module in MD doesn't work. This step is for checking the
LASER TRACKING ACTUATOR.
4-4. LASER TRACKING ACTUATOR
4-4-1. Solution
Please check and replace IC407, IC408 on MAIN board.
4-4-2. How to troubleshoot (Countermeasure)
The tracking actuator makes the laser beam be positioned in the center of a track on CD disc.
1) Check the TRD signal from Pin22 of IC407.
  If no signal, check 3.3 V(RF) and X400.
2) Check TR- & TR+ from IC408 to CN408 for driving the tracking actuator.
  If no signal, check +1.8 V and +5 V for IC408.
3) Check if the FFC cable is solidly connected between CN405 and MD.
4) Check the MD.
  If the pickup module has any trouble, it can not move the laser beam on the left or right side.
Please check the function after changing another MD.
4-4-3. Service hint (Any picture / Remark)
< Waveform of TR±
for driving TRACKING actuator >
ONE POINT REPAIR GUIDE
TR-
Pin15 to CN405
Pin16 to CN405
< Signal check point >
3-9
TR+