My sony ericsion c702 have a problem phone switch on ,then display and keypad light ok.but after 30 second display and keypad light out.but phone on

Sir there is only solution please go to sony service centre or to a repairer,!@!!

I have this problem as well except the keypad light and screen instantly turns off. Everything works except I couldnt see the what im doing. I figured it out and the keypad membrane seems to be the problem. I changed it and everything works perfectly. Dont know if you still care about this even after 2 years but at least you know.