Boot loop after replacing main motherboard and flashing firmware

Hi there,

My Sony bravia kd55xd8005 stopped turning on about 6 months ago.

Last week I decided to start having a poke around to see if I could fix it. From what I read online at the time a lack of status led and screen turning on could have been either the power supply or the main board.

I removed the cable going from the power supply to the main board and the led panel lit up white, again reading online that suggests that it's the main board. So I replaced the main board.

The led indicator started glowing green and orange when I plugged it in and I could hear the original instal music (birds and a waterfall). Great! But no display.

I went back to Google and read flashing the firmware should fix it. So I tried that.

Now the Sony logo comes up the android icons come up and then it restarts. So I Google again, try factory resetting. No luck, reboots after 5s of the big ring coming up.

"Try updating firmware again by renaming file to update_package.api"

So here we are now, the update bar is getting about 1/5 of the way along before the TV restarts again, tries to boot normally, restarts and tries to update again.

Any idea what my next step should be?