Boot loop? QN70Q6DTAFXZA

@john65845 just so we don't get confused, which is pretty easy for me, I thought I post an image of some basics as I understand it.

Now you disconnect the flat ribbon cable from teh Driver board 2 and the bootloop stops backlights turn on like they should. Sound like on of the three driver boards are having an issue. (yes, for all the experts that may read this, it can always be the panel too, but we keep our fingers crossed ;-)

Now, I'd proceed by disconnecting the interconnect flex cable between driver board 1 and driver board 2. Reconnect the flat ribbon cable to board 2 and then power the TV up. No boot loop and backlight on would mean bord 1 is the prime suspect. If it is the same as before, disconnect the power, reconnect interconnect flex cable between board 1 and 2. Then disconnect interconnect cable between 2 and 3. keep the flat ribbon cable connected to board 2. Reconnect the power and power on. If the results are as before, then I would focus on board 2. If the results are that boot loop stopped and backlight is on, then it is board 3.

Sadly it does only narrow it down somewhat and only sometimes. It doesn't help on a component level. I do know that those interconnect flex cables can be a PITA and can actually be the cause.

Measuring Capacitors in circuit is possible but not great for accuracy. It's always better to remove them. Here is the problem. there are no schematics for these boards, that I have ever found any. It may be easier to determine a failed component by either using a thermal camera, or if you are frugal like me a Rosin Vaporizer (Atomizer), isf it heats up. Now there are thermal cameras for the smartphones but I believe that these are mostly for Androids and still a bit costly. No, not terrible expensive but still a lot of money if you do not use it often.

Hope this makes sense and that I answered your question.