Chosen Solution
Hi, I do small repairs on small devices but this is for MY IPHONE, embarrassing as I can’t fix it to date. It just died one day….. and I mean its DEAD, No response at all and the USB meter shows no current draw whatsoever. I know that this is a board level repair as I have placed the board in a working housing and still no difference. i.e. good battery, dock, screen etc. everything but the board! I have checked for shorts on power lines and have not seen any at all. The board also looks good under the scope (nothing physically damaged - why would it it just died!) Now as I last saw the device working before I plugged it into a car charger (yes a crappy one!) I suspected a TRiSTAR problem. So I replaced this IC and no difference, still DEAD no current draw. All posts and forums suggest for a completely dead device either a short of U2 Tristar… I am now thinking of the Power Management and Big Power Management IC’s. Has anyone else seen anything like this before and have any recommendations before I try these in desperation? Any help very much appreciated…. Nathan
As you suspect, this is very likely a U2 problem. Depending on how experienced you are with this kind of repair, it is possible that you either have a defective replacement IC or it was not properly soldered with all pins connecting. If you applied too much heat, you may have shorted some solder balls underneath neighbouring chips or on the other side of the logic board. You may also have blown off some components. Just ideas to check against…if you are experienced, you probably already verified this stuff, if not, then this is as good a time as any to learn :>). U2 primarily functions as a communication chip. Tigris is responsible for generating PP_VCC_MAIN from either the battery or Lightning cable. The PMIC generates a multitude of power rails. Ideally, you need to test them all to ascertain full functionality.
connect just the battery, press the power button and check pp_vcc_main, if you get the current. now remove the battery and connect just charging port and check if there is 5v but no pp_vcc_main. check L1401you.
