Hi,
I cannot find a schematic for the board (EAX64905301 (2.3) to find out why the diode overheated but looking at the board it appears to be connected to the primary side of the power supply between the transformer and the power switching transistors.
You could check if the power transistors near the diode are short circuit or not and also check if the fuse blew at all.
After that if the transistors test OK then try testing the capacitors around the diodes to make sure that they’re not short circuit either.
If all test OK then perhaps it was just a case of the diode failing. You could try just replacing it (use the specs from the one next to it) and check what happens ;-)
Other than that, without a schematic the easiest option is to replace the board.
I found a [https://www.ebay.co.uk/itm/POWER-SUPPLY-42LN5400-42LN540V-42LN578-TV-EAX64905301-2-3-REV3-0-LGP42-13PL1/124037111747?hash=item1ce1301fc3:g:3EcAAOSwLWBeFyim|board], no doubt the same one as you found. If you live near Bolton you could always ask if local pickup is available to save the shipping cost