Vfd Is Not Displayed When Power On The Set - LG CM4740 Service Manual

3. VFD IS NOT DISPLAYED WHEN POWER ON THE SET

When power on the set, any icons or characters on VFD are not displayed.
3-1. VFD
3-1-1. Solution
Please check and replace DIG302 on FRONT board.
3-1-2. How to troubleshoot (Countermeasure)
1) Check if VKK, FL+ and FL- are output from SMPS to VFD via the MAIN board.
2) Check if IC501 outputs VFD_D0, VFD_CLK and VFD_STB to the FRONT board.
3) Check the GR signal(pulse signal) of IC408 on the FRONT board.
Check the SG signal(pulse signal) of IC408 on the FRONT board.
If the GR and SG signal isn't output, replace IC408 with a new one.
If the GR and SG signal is output, replace DIG302 with a new one.
3-1-3. Service hint (Any picture / Remark)
GR signal
SG signal
ONE POINT REPAIR GUIDE
Click the picture,
and then drag to enlarge it.
Check the waveform on details.
GR SIGNAL
ABOUT 30V
< Waveform of GR and SG signal >
3-5
SG SIGNAL
ABOUT 30V