So I have been doing my own research of course. Sadly it does not appear to be straight forward. Here is what I have found so far
1) Using lg.encompass.com, linked from the LG website as an authorized midwest retailer, searching for 65EF9500UA-AUSZLJR, it provides EBT64006605 "Chassis Assembly". It lists as an equivalent EBT64006602 - Chassis Assembly. It does not in any way say why you might want one or the other. The picture of the 6602 shows some extra cables and what appears to be some extra plastic at the bottom. I don't think i need the plastic, I have that piece already and it's not broken. The later number - 05 versus 02, makes me wonder whether the 6605 is a newer board revision. Maybe the 6605 fixes the issues that caused my board to die and the 6602 will just blow the same way again? The 6605 is backordered for 2 months. The 6602 is available in 3 days. Anyone know the difference or have any contacts or insider info they can leverage? I am not sure I can wait 2 months for the 6605. I definitely can't wait that long if I get there and then it's still not in stock.
To further complicate matters, lg.encompass.com also lists EBU63457401 as equivalent to EBT64006602, but is out of stock for 60 days. It then lists CRB35228701 as equivalent to EBU6345740. That one is "Bpr Total Assembly,refurbished Board" so I presume it to be a refurbished 6602 board. Out of stock for 60 days.
2) A different authorized supplier - Andrews Electronics (west US) - their website says EBT64006605 is the right part but that it has been substituted with EBT64006602. It does not even give the chance to order 6605, it wants you to go to 6602. When you get to the 6602 listing, it then says that has been substituted with CRB35648501 "CHASSIS ASSEMBLY,REF" - which I take to also mean Refurbished. So Andrews doesn't give you the ability to buy either the 6602 or 6605 board. It's the refurb only, and that is maybe in stock in 5 days time.
Sadly ebay does not appear to have any of these.
Not sure what to do. I've got the TV in pieces and I've reinserted all the ribbon cables and connectors. No improvement (but at least I didn't make it worse) and I can see how replacing the board is going to be an easy job, so I am reluctant to get an LG service call going and pay a massive premium for this.