Vfd Is Not Displayed When Power On The Set - LG OK99 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 (VFD801)
3-1-1. Solution
Please check and replace DIG300 on FRONT board.
3-1-2. How to troubleshoot (Countermeasure)
1) Check if VFD_12V, DVCC_3.3V and DV_5V are output from MAIN to VFD via the TOP board.
2) Check if the IC501 outputs VFD_CLK, VFD_STB, and VFD_DO to the TOP board(CN804 pin33~35).
3) Check if the VFD grid current amplifier circuit on the TOP board.
Check the drive signal to the transistor's(Q801, Q802) base.
 If the control signals from VFD (SW) isn't output, replace VFD with a new one.
VFD heat rays is RED : DVCC_5V(IC201 check) Voltage will be high than 5.5V
No VFD : VH(VFD801 pin27) will be not supply about 30V.
No VFD : VFD 12V will be not supply (Check Q205).
3-1-3. Service hint (Any picture / Remark)
VCC_5V
DGND
DVCC_3.3V
DVCC_3.3V
VFD_12V
VFD_CLK
VFD_STB
VFD_DO
+3.3VA
ONE POINT REPAIR GUIDE
VCC_5V
40 DV_5.0V
39
DGND
38
DV_3.3V
37
DGND
VFD_12V
36
VF_12V
VFD_CLK
35
VFD_CLK
VFD_STB
34
VFD_STB
VFD_D0
33
VFD_DAT
+3.3VA
32
3.3VA
CN804
< CN804 >
Q801, Q802 Base
< Waveform of the grid current driver>
3-5
Copyright © 2018 LG Electronics Inc. All rights reserved.
about
12Vp- p
Only for training and service purposes.