MacBook Backlight not working

I was using my macbook and suddenly i felt screen is flickering and then display went off, after that i tried everything like PRAM reset, SMC reset, nothing worked for me but the macbook was working fine with external display i thought my display isn't working, I went to apple service center, and they said my lcd is working because if we put flashlight on apple logo we can see that much part of display working fine but just because its backlight isn't working i need to change the whole motherboard, which is way too costly, please suggest me the solution, i cant spend money for motherboard replacement.