Do you have a question about the Hitachi 55HK6T64U and is the answer not in the manual?
TV working, LED normal, but no picture and backlight on the panel.
TV not booting or hanging in standby mode, indicating a potential short on VCC voltages.
No audio at main TV speaker outputs; check supply voltages, headphone connector, or detect circuit.
Device cannot boot or TV hangs in standby mode; check power supply and SW.