Did you ever find a solution to this? I (along with many others I’m finding) am having this exact same issue recently which leads me to believe it is most likely a firmware issue and nothing hardware related (unless these TVs were all designed to fail at the same time!) - I tried flashing the firmware that Toshiba has on their website but it goes to 20% and fails…I’m guessing this is due to the firmware being an old version and the TV not allowing a downgrade - that said has anyone found a firmware that will work? The version I tried is 20170830113420_update_casttv_uhd_01.04.088_fy17_sc_init_clear.prg which is obviously an old (possibly the original) version. Anyone with a working version out there? My model # is 55L621U. Thanks much!