Sony 5 blink error, only boots when T-Con to left panel disconnected.

My Sony XBR-65X750D has a 5 blink error code. The backlight turns on but shuts off after about 10 seconds when the error code starts. When I disconnect the t-con cable to the right side of the panel it still gives the error code. When I disconnect the t-con cable to the left side of the panel the TV boots up. After booting up, for about a week there was only audio, but now the picture has started working on the connected (right) side.

I bought replacement t-con and main boards, which I tried, but they didn’t make any difference. I opened the diagnostic screen, which shows an error, but since I can’t see the left side of the screen I don’t know what it is :(

Any suggestions for where to go next? At this point I assume it’s either the power supply board or the panel driver board. As far as I can see there are no visible signs of failure on any of the boards. I’m learning as I go and haven’t found any service documentation on this particular TV so I’m not really sure what to test next.