2. The power supply circuit of the TV is abnormal, resulting in the Sony logo of Sony TV not being bright.
3. The TV is switched to other signal sources, which is inconsistent with the video signal output by the set-top box, resulting in the Sony logo of Sony TV not being lit.
4. The set-top box is not turned on, resulting in the Sony logo of Sony TV not being lit.
5. The backlight of the TV screen is broken or other special circumstances cause the Sony logo of Sony TV not to be bright.
6. There is a virtual welding fault in the screen drive circuit inside the TV.