LG CMS8450F/W Service Manual page 37

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 servo motors in MD don't work. This step is for checking the tray open/close motor
among them.
9-3. TRAY OPEN/ CLOSE MOTOR
9-3-1. Solution
Replace IC401 or IC400 on MAIN board.
9-3-2. How to troubleshoot (Countermeasure)
1) Check MOT_OPEN & MOT_CLOSE signals from pin K4 & L4 of IC501 to IC400.
  If no signal, check +1.8 V & + 5 V to IC400.
2) Check LOAD ± from IC400 to CN401 for driving the tray open/ close motor. It is about 3.85 Vp-p.
  If no signal, check +5 V to IC401. If it has any trouble, replace it with a new one.
3) Check if the FFC cable is solidly connected between CN401 and MD.
4) Check the MD.
  If the tray motor is short-circuit or has any trouble, it can not open or close the tray.
Please check the function after changing another MD.
9-3-3. Service hint (Any picture / Remark)
< Waveform
for driving TRAY open/ close motor >
ONE POINT REPAIR GUIDE
MOT_CLOSE MOT_CLOSE
pin6 of IC400 pin6 of IC400
3-16
MOT_OPEN MOT_OPEN
pin7 of IC400 pin7 of IC400
< MAIN board top view >
LO+ LO+
pin4 of CN401 pin4 of CN401
LO- LO-
pin2 of CN401 pin2 of CN401