LG CM4550 Service Manual page 25

4. 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
SPINDLE MOTOR among them.
4-1. SPINDLE MOTOR
4-1-1. Solution
Please check and replace IC407, IC408 on MAIN board.
4-1-2. How to troubleshoot (Countermeasure)
1) Check the SPDO signal from pin24 of IC407.
  If no signal, check 3.3 V(RF) and X400.
2) Check the SPIN- & SPIN+ from IC408 to CN405 for driving SPINDLE motor. It is about 3.6 Vp-p.
  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 spindle motor is sort-circuit or has any trouble, it can not rotate CD discs.
Please check the function after changing another MD.
4-1-3. Service hint (Any picture / Remark)
< Waveform of SP- & SP+
for driving SPINDLE motor >
ONE POINT REPAIR GUIDE
About 3.6 Vpp
Sp+
Pin17 to CN405
< Signal check point >
3-6
Sp-
Pin18 to CN405