I'm not sure if everyone's looks the same as mine inside, I purchased mine on ebay "refurbished" and it was dead on arrival. Same issue, one blue blink, wouldn't power on, charged it, charged it, charged it, tried all the troubleshooting steps to reset the hardware. Nothing worked.
Upon opening it up I noticed it was a pretty messy bundle of wires and a lot of the ends of the magnet wire that didn't look insulated (closer to the solder joint, silver wire not colored) were able to short out a lot of the spots on the board, as well as the pins on the ribbon connector. There was a wire that pressed right up against the ribbon connector when the headphones were closed back up.
I cut small pieces of kapton tape and covered all the parts of the board using tweezers, sliding them under any wires that ran over those areas. I covered the ribbon connector, etc etc. Just doing my best to make sure nothing could make contact. There was a small foam pad as well, I saw in someone else's post somewhere else that it helped to apply a little pressure against that part of the board and the foam had been pretty compressed, so I added a square of thin adhesive EVA foam I had from Michael's (it's 99 cents for a 8 1/2x11 sheet. Headphones worked really well after that. I have logged 600 hours, 25 mins in the Sony app with these headphones so far. Now my only complaint is the annoying creaking sound the hinges make. That will be my next fix.