Chosen Solution
Hi guys, I have an iPhone 6 Plus here, Phone is not water damaged, it won’t turn on, not charging. Not screen or battery issue. It’s motherboard problem. Upon diagnosis, I found PP1V8_SDRAM has problem. It’s not shorted, but resistance value is very low. The cap C1739 only has 0.006 ohm, it’s almost shorted to ground. I used freeze spray, but couldn’t find any bad component. I removed Tristar chip, made no difference, PP1V8_SDRAM still has very low resistance value. Don’t know where to check next. Can anyone help please? Many thanks.
Hmmm…I doubt your meter has enough resolution to measure 0.006 Ohms. Perhaps you are referring to diode mode readings, which would be 0.006V. Either way, that seems low. A normal diode-mode reading for PP1V8_SDRAM is ~0.330V. Unfortunately, that lines goes to a lot of places; Tristar, Tigris, Backlight, Audio, PMIC, SDRAM, CPU along with a whole host of caps. At this point, you need to take into consideration what the failure mode and history was to guide you a bit. Otherwise, you’ll just have to pull components until you find the guilty party. Start by the easiest and move on towards the hardest. You could also remove L1216 to isolate the PMIC output from the downstream circuitry to see if the short is upstream (PMIC) or downstream (something else). Then you could inject 1.8V from a DCPS and slowly crank up the current until freeze spray shows you the bad guy.
