A shorted VGH or VGL rail can overload the DC-DC converter. Using the schematic, you measure resistance from the VGH pin to ground. If it is near 0 ohms, you remove capacitors listed in the VGH section one by one.
The "3V/5V Standby" circuit must be active before you press the power button. e89382 hannstar j mv-4 94v-0 schematic diagram
Often not the TCON itself, but the schematic helps rule out the "BLON" (Backlight On) signal path. The schematic will trace the enable pin from the input connector to the backlight driver IC. A shorted VGH or VGL rail can overload the DC-DC converter