Why does my Sony Bravia LCD KDL-40BX421 TV spontaneously reboots itself?

https://www.youtube.com/watch?v=AuWhoi5--2o
It's usually because your remote batteries are low. Remotes are known to send off some weird signals when they're on the last bit of juice. Your TV could be interpreting infrared noise from your remote as an "On" command. The power button on the remote or the TV itself could be stuck. https://www.quora.com/Why-would-a-TV-turn-off-and-on-by-itself
Samsung
Try to update the software.In some cases, a software update can correct the problem. ... If the TV turns off during the software update, it could damage the TV. Updates can take up to 30 minutes depending on network speed, so if the TV is not turning off too frequently, try updating the software.
https://www.samsung.com/us/support/troubleshooting/TSG01108742/
LG:
A TV that intermittently powers on or off is usually caused by the timer setting. ... Check if the TV power cord is securely plugged into the wall outlet or the power bar. 3. Time menu options affect TVs turning on or off automatically.
https://www.lg.com/ca_en/support/product-help/CT20098005-1412238468277-intermittent-power-or-powers-off-on
SONY:
Your Sony BRAVIA KDL-46XBR9 TV may reboot due to a damaged AC power cord. In this case you can usually resolve the rebooting problem by replacing the power cord. Your Sony BRAVIA TV may also reboot because of a bad power supply in the TV. ... The BRAVIA KDL-46XBR9 may also reboot because of incorrect settings on the TV.
https://www.techwalla.com/articles/why-is-my-sony-bravia-kdl-46xbr9-rebooting

Thin vertical lines cover screen on Samsung LCD - AVS Forum ' Home ...

www.avsforum.com/.../1127410-thin-vertical-lines-cover-screen-samsun...

Mar 7, 2009 - 30 posts - ‎25 authors
Hi guys, Ive had this TV for about a year now - all of a sudden thin vertical lines havecovered my screen (show in link below) No matter what ...Missing: 40bx421

TV Repair Help for Vertical & Horizontal Lines on Your TV ...

? 2:47
https://www.youtube.com/watch?v=b0sI7LB4cZE
Apr 25, 2014 - Uploaded by ShopJimmy.com
TV Repair help with troubleshooting lines on your TV Screen. ... hi i have a sony bravia mdel # KDL46EX523. i have horizontal multi colored lines ... My TV has the following symptoms: - Horizontal lines from top to bottom of .... thick(like 1-1/12 inch) and a couple of green vertical lines next to the black one.Missing: kdl ‎40bx421

Flat Screen TV Has Lines Going Through Screen - Possible ...

Replace main board

What you've heard is right. This is a main system control memory IC fault itself.

probably the ba board for the same ahs gone bad
the same has happended to my sony v series bravia also and have to be replaced on our own csot as this si not covered under any warranyt

The Bravia would shut-off and restart after about a minute of operation repeatedly. I removed the internet connection cable and the problem stopped.

Problems relating to the automatic turn on and turn off of a set like this usually point to the main board being an issue. For this set, I believe Sony refers to that board as the "AU" board.

It's probably not the G/Power Supply board, especially if it turns itself on. Power supplies will turn a set off, but rarely--rarely--turn itself on.

If there's no kind of extended warranty involved here,
you could be looking at $500.00 for parts and labor to repair this kind of problem.

As always, try any software/firmware updates Sony might have available on their website prior to pursuing a repair visit.

turn cc on receiver

Replaced circuit board under warranty.

Replace the BU Mount pcb. Sometimes they are called the FB pcb.