The backlight is separate, with a separate inverter chip. Either the backlight material has arced over and died or the PSU is dead - or both (one killing the other). Schematics aren't available, but you can try unplugging the backlight connector and checking with an AC voltmeter the output voltage. My previous email of 1000v was a bit OTT, I think it's more like 200-250v AC at very low current.

I don't know what the service stock of RR's is like, but it'd be worth asking them before returning it!

Hugo