Hi Alfred Grace,
First of all, thank you for posting your question here at Fixya.
Based on the symptoms you've described, I don't believe that the backlights are already faulty. If backlights gone to malfunction, that are permanent, but in your case you've said that the TV power up fine for half an hour, this is an indication that the fault not came from the backlights but from the inverter boards. Inverter boards are the one giving high voltage to the backlight to light up, it has a built in protection circuit that will activate once there's a malfunction on the board to avoid further damaged because of high voltage output.
If you would like to fix it yourself, I would advice you to replace both the slave and master inverter board. I saw your board at shopjimmy.com. Click it HERE
for the replacement. Replacing these boards are not technical, all you have to do is to unplug the unit overnight to drain any voltages from the power supply board, disconnect all connectors and then put-in the new boards. No soldering required. If just in case that the inverter boards are not the issue (I'm pretty confident that the power supply board is working fine), don't worry, the link I've provided accepted return, the fault is on the power supply board.
Hope I helped you.
Have a nice day!
Good luck and take care!