Replaced motor phone not vibrating
recently my phone stopped vibrating, after replacing vibrating motor it worked for about a month and stopped again. i ordered another motor and replaced. phone still doesn't vibrate. thinking it's a bad part i ordered another one but it didn't work either.
got a friend with iphone 4 and used his motor in my phone, no luck. put the motor back into his phone and it works fine.
what else could it be that prevents my phone from vibrating?