U2IC testing options?, No Apple logo may not always be the indicator

U2IC testing options?, No Apple logo may not always be the indicator

ok so i have been testing some iphone 5 5C 5S 6 boards for U2 IC failure . Any phones that come in i would disconnect battery and connect to power via the dock connector. if the apple logo does not appear then that would be an quick indication of U2IC failure, or so i thought.