LG CM9750 Service Manual page 30

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.
8-3. SERIAL FLASH (IC503)
8-3-1. Solution
Please check and replace IC503 on MAIN board.
8-3-2. How to troubleshoot (Countermeasure)
1) If the crystal(X500) does oscillate, Check Serial Flash(IC503) on MAIN board.
  Check 8pin(VCC), 6pin(CLK), 1pin(CS), 2pin(DO), 5pin(DI) of below waveform.
2) If pin8, 6, 1, 2, 5 doesn't come out, Check damping resistor(R564, R563, R535, R536, R534) of IC503.
  If damping resistor of IC503 is OK, then replace IC503. (it need to download program)
3) After change IC503, if It is still not below waveform, Check IC501(DSP IC).
8-3-3. Service hint (Any picture / Remark)
IC503 IC503
< MAIN board bottom view >
ONE POINT REPAIR GUIDE
3-11
V V CC
CS#
CLK
DO
< Signal waveform >