I had this issue where backlight would go off randomly, sometimes would work ok for an hour or so then go off (shining torch on the panel showed desktop).

I measured the backlight board supply, PWM and BLON pins while in the fault state and these were in a state where backlight should have been on but wasnt. So in my case definitely the backlight board (inverter).

The board is mostly solid state but there are 4 caps on it and it runs pretty hot, so I removed and tested the caps half way down the board and these measured ok, but the two near the power connector at the top seemed iffy. So I changed them - 270uF @35v (didnt have correct values so used some a little bigger) and its been ok since.

I know theres some variations on this board so might be different fault on others, but mine was V267-604HF

Hope this helps someone else. Its about £40 for new board and caps are a few pence so this is a cheap fix if you have the skills.

UPDATE:

This didn't last - although did last a fair while. In the end it was the backlight strips in the LCD itself!

I was fortunate enough to find them on AliExpress for very little money. A right fiddle to change though not for the faint hearted! The LEDs on the strips I removed had cracks in them when viewed with a magnifying glass even though they all worked.

And measuring current draw on individual LEDs, many drew more current than others.

So the backlight board is switching off due to excessive current draw.