Vfd Is Not Displayed When Power On The Set - LG CM9750 Service Manual

4. VFD IS NOT DISPLAYED WHEN POWER ON THE SET

When power on the set, any icons or characters on VFD are not displayed.
4-1. VFD (VFD301)
4-1-1. Solution
Please check and replace VFD301 on FRONT board.
4-1-2. How to troubleshoot (Countermeasure)
1) Check if 39 V, FL+ and FL- are output from SMPS to VFD via the MAIN board.
2) Check if the IC501 outputs VFD_RST, VFD_CLK, VFD_DO, and VFD_STB to the FRONT board.
3) Check if the VFD grid current amplifier circuit on the FRONT board.
Check the drive signal to the transistor's base.
  If the control signals from VFD (DGND_2, VH, VDD) isn't output, replace VFD with a new one.
4-1-3. Service hint (Any picture / Remark)
< FRONT circuit >
ONE POINT REPAIR GUIDE
CN315 CN315
VFD_STB, VFD_STB,
VFD_CLK, VFD_CLK,
VFD_DO VFD_DO
R327(TP304)
Q301 Emitter
< Waveform of the grid current driver>
3-5
about
30 Vp-p