LG CMS9540F Service Manual page 27

4. 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.
4-1. NO VCC33, VCC12
4-1-1. Solution
Please check and replace IC505, IC509 on MAIN board.
4-1-2. 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 pinB2 of IC501 & R524, R5F7.
3) If PWR_CTRL is high, check R5F6, R5F4, R5F5 and if there's no defective component then replace IC505.
4) If 3.3 V (VCC33) is normal, check 1.2 V output (pin2, 4) voltage of IC509.
If 1.2 V of IC509 pin2, 4 doesn't come out, then replace IC509.
4-1-3. Service hint (Any picture / Remark)
IC505
D501
ONE POINT REPAIR GUIDE
< MAIN board top view >
3-6
IC509