Update March 2017: The bug has been fixed after almost after four months of having this nasty bug on your TV (Fix: 4/18/2017 Version PKG3.865.0136NA). Some countries (like mine) does not haven an update yet.
Sony updated some TV's to Android 6.0 on mid-December of 2016. This update introduced a bug on some TV's. The TV will no longer turn on (quickly) after a period of time that it is turned off.
Symptom: The TV won't turn on with the remote's power button. On my case the bottom light of the TV will remain in color yellow, and the power buttons just remain unresponsive. After 4 minutes of waiting the light will turn off and the TV will restart complete showing the Android boot animation logo.
It is very annoying since you can not quickly turn on your TV.
Sony's Support: Sony support may suggestion your two things:
1) To make a factory reset of the TV. With this the TV will work fine for a week and after that the bug will show up again.
2) They may change your mainboard, but when it get updated again to version 6.0, the bug will show up again.
Cause: Complaining around on the Sony forum some user found which component may be the issue of the bug. If you turn off the Wifi of the TV, the bug will not show. At the same time it will cripple the TV since wifi it is very important, but it is very interesting that the possible cause of the issue was found.
Affected Models: For the moment this are the affected models reported on the forum:
KDL-50W800C - SVPDTV15_UC-user 6.0.1 MMB29V.S4.3.709 release-keys.
KDL-50W809C - 6.0.1 - PKG3.707.0120BRA - SVPDTV15_BR-user 6.0.1 MMB29V.S3 3.707 release-keys.
KDL-55W800C - PKG3.709.0120NAA
Sony told on the forum that the bug has been recognized, but it haven't post a fix for the issue in four months.