LG CM9750 Service Manual page 28

8. NO BOOTING IN CD/USB FUNCTION
After you turn on power key and displayed message in the following order (HELLO  VOL XX 
CD or USB) on VFD, it will not display other message on VFD, and it will not boot-up normally.
8-1. NO VCC33, VCC12
8-1-1. Solution
Please check and replace IC505, IC500 on MAIN board.
8-1-2. How to troubleshoot (Countermeasure)
1) Check Voltage of IC505 pin3 on MAIN board.
  If IC505 pin3(about 4.9 V) & D500 Input 5.6 VA doesn't come out, check 5.6 VA from SMPS board.
2) If IC505 pin3(about 4.9 V) is normal, check the PWR_CTRL(IC505 pin2) is high (about 3.3 V)
  If PWR_CTRL isn't high, check pin B2 of IC501 & R524, R522
3) If PWR_CTRL is high, check R524 and if there's no defective component then replace IC505.
4) If 3.3 V(VCC33) is normal, check 1.2 V output(pin2) voltage of IC500
  If 1.2 V of IC500 pin2 doesn't come out, then replace IC500.
8-1-3. Service hint (Any picture / Remark)
ONE POINT REPAIR GUIDE
< MAIN board top view >
IC505 IC505
< MAIN board bottom view >
IC500 IC500
D500 D500
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