4 
1 iPhone 6s - Dead - 20ma draw from battery or 437ma (0.44A)when plugged
Hi all
I have an iPhone 6s that I’m really struggling to get it to boot. The phone was water damaged and has been ultrasonic cleaned. It doesn’t look too bad, mainly just had signs of water around the WiFi IC, a little around the backlight driver (but doesn’t seem enough to have penetrated the huge amounts of conformal coating/glue or whatever it is that’s normal in that area!) and also at the very bottom of the board below Tigris. So I suspect water had got in near the camera at the top and near the speaker at the bottom.
When plugged into the DCPS I get 0.00A (good start) but then on prompt to boot I only get 0.02/0.03A so about 20ma. When I test with a lightening cable I instantly get 0.437A (through the usb cable) as soon as I plug the cable in, and it then just stays like that.
i’ve checked the voltage and diode readings on all power rails and I can’t find anything wrong, besides PP_CPU gets a constant 0.898v whereas a known good board fluctuates from around 0.5v+ but I think this is probably not the cause of the fault but an effect. I did find 2 capacitors that were bad on VCC main which I’ve removed, they were C5283_RF and C5284_RF near the WIFI IC, they were causing the diode reading on VCC main to drop, I’ve not yet replaced them.
Does anyone have any advice on what to try next?
As always, really appreciate advice on this.
Thanks
Ist dies eine gute Frage?
1 
Are you using a squid or ipower out of your dcps? It is best to use a squid as the ipowers are not much good for low power readings.
von Chris Stables
Hi Chris, I'm using a standard squid cable.
von Darren
As I've found a few other threads on various sites with the same/very similar issue which don't seem to have been resolved, and I've convinced myself now that this is economically unrepairable I'm going to use it for experimenting to help further my understanding/skils and help to repair if I get others like this. My plan is to start removing all "non critical" ICs/components one by one until it boots, checking what changes/if anything changes each time. I'm thinking it might be best to repace Tristar and Tigris before I try that, or I could wait until there's nothing non critical left to remove. I'll probably start by removing things like the backlight driver and audio and taptic ICs.
I may need to post a seperate thread to get ideas of what ICs are critical to boot. I know the schematic labels the critical components but they're not just for booting. So far I'm thinking the critical ICs are Tigris, Tristar, CPU, PMU, Baseband. Anyone have any more that I shouldn't remove if I want it to boot?
von Darren
Once I have an idea of the minimum ICs required to boot, I then can see what lines these ICs are on and therefore I'll have a list of the critical lines that can not have any faults on them (otherwise may prevent booting) if there is any fault on any line that would prevent booting then I'd need to consider these lines critical. Once I've effectively isolated the critical components, I can then rule out anything that's on any non critical lines.
I'm guessing this must be a similar approach to those that offer data recovery, where the aim is not to end up with a fully functioning phone, just one that will boot and allow the data to be recovered.
If anyone has any insight to this I'd love to hear it.
Thanks
von Darren
Hi Darren, as I mentioned in my previous (troubleshooting) answer, I've seen a few of these 6S-No-obvious-failures-yet-wont-boot phones. My only logical conclusion has been that this is a CPU/SDRAM or inner trace issue.
Of course, I encourage you to play around with this device to learn, at the very least, you can keep practicing on removing and reballing more complex IC's.
von Minho
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