LG OM7550 - Vfd Is Not Displayed When Power on the Set

3-5
ONE POINT REPAIR GUIDE
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 (DIG300)
4-1-1. Solution
Please check and replace DIG300 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_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, VDD) isn’t output, replace VFD with a new one.
4-1-3. Service hint (Any picture / Remark)
R327(TP304)
Q301 Emitter
about
30 Vp-p
< VFD schematic > < Waveform of the grid current driver>
CN3E14
CN3E14
VFD_D0,
VFD_D0,
VFD_STB,
VFD_STB,
VFD_CLK
VFD_CLK