Hi Ben,
Your error codes point to a failed SC board. Try this to verify:
Remove connectors between SU/SD and SC boards. Remove all screws securing SU/SD and fold the boards away from the SC. DO NOT remove the flat brown leads to the display or you'll spend half a day getting them back correctly. Locate socket SC20 on SC and short out the 2 pins.
Switch the TV on. If the set powers on to a solid green standby light, SC is OK and a green LED should light up on the SC. If you still get code 7, then the SC is knackered. It can cause codes 4, 5, 6, 7 and 10 and not necessarily from shorted FETs &/or diodes. I assume you've checked all of them on the SC.
My only concern is code 8 which is a SS board fault, but it might be normal with SC20 disconnected. Of course, if code 7 is cleared in the above test, then you have a faulty SU &/or SD, but we'll cross that bridge when we come to it. See how you go with that for starters. - Bruce