Presario CQ61 417-SA display issue

Eldest used this laptop for uni, until the display became too dim. Bought him a new Ativ and recovered his coursework using an external monitor.

It runs Win 7 Home Premium which in passing I have reinstalled from the HP onboard image, with a view to disposal. No hardware issues are indicated post install.

I thought that since the screen image is just about visible that it would simply be an issue of replacing the inverter, but no. I have just received and installed the second inverter from an Ebay seller with 100% feedback and it is still rather like me exceptionally dim.

What else could account for this? TIA

Are you sure the backlight hasn't failed? Some info on ebay about screen issues