Posts on badcaps.net indicates a common failure with this TV is caused by dirty contacts on a relay and a blown cement fusible resistor. To diagnose this failure, check all fuses on the power supply board PE0702A and the resistance of the large white rectangular resistor R850 marked RGDU5M-5E (1.8 ohm 2.8W Noble fusible resistor). The only place I could find an equivalent part was on ebay (search “RGDU5M-5E”). You also need to clean the relay contacts for SR80. It is a black rectangular part located near R850. To clean the contacts, remove the plastic cover on the part by grasping up on the sides. Slide a business card between the contacts and move it around while gently pressing the contacts closed. After cleaning SR80 and replacing R850, check that the 5V standby is stable by probing the main connector. If it isn’t, Q880 needs to be replaced. This part is STRY6456 and can also be found on ebay. Make sure the pins are straight and not right-angled. The bridge rectifier (D8820) could also be damaged but this failure is less common. You may also notice browning around R827 and R828 but these parts tend to be ok.
Update: The equivalent part Ohmite TWW3J2R0E (2.0 ohm, 3W) can be found at Digikey (part# TWW3J2R0E-ND) and Mouser. You can also substitute the 5W version TWW5J2R0E.
Youtube video from Tampatec below on this problem but he doesn’t mention cleaning the relays.
Other models using this power supply board are 46XV648U, 47ZV650U, 52XV648U, 55SV670U and 55ZV655U.