Backlight not working. No sign of water damage.

My brother gave me his old iphone as he said it wasn't working. I had a look and thought it was dead at first but then realised it was very very dim. Have done my homework and scoured the internet for solutions. Have tried brightness settings, soft and hard resets, cleaning lcd connector to logic board and now finally looked underneath the emi shields. There looks to be no water damage as all indicators on phone are white and bro says he didn't drop it in water etc.. Any ideas on an answer? Tomorrow i will be trying a friends lcd with my iphone to check whether its the screen or the phone.