Chosen Solution
Hi! I would be grateful for your advice on troubleshooting this problem; I was using my iPhone 6 plus, and the top right corner of the screen went dim. I thought this meant I would need a new screen. However, within 10 seconds it felt warm on the back of the metal case (where the motherboard is). The battery was 45% charged and went down to 36% within seconds. I pressed the power button to switch off the screen; the metal case got hotter, and when I switched the screen on again, the battery had fallen to 30%. I did ‘slide to shut down’, and located my iphone tools. The phone continued to get hotter even when fully shut down; at about 60 seconds since the backlight went dim I opened the phone and quickly unplugged the battery connector. The phone rapidly cooled down once I had done this. The motherboard was very hot at the top, as was the metal case in the same area. The battery was very slightly warm, and a bit warmer where the hot motherboard was touching it. This phone is (was!) in mint condition; I’ve never opened it, and it has all original parts. If the battery had been full (or even charging), this fault would probably have caused a fire - especially since whatever kind of short circuit it was, continued to generate heat even when the phone was ‘fully’ shut down, so I am lucky I was using it when this happened! I would be grateful for advice, or if anyone has had the same problem (backlight failure with sudden battery drain and overheating). I have repaired iphones all the way up to 5S in my spare time, but this is the first time I have opened a 6. It has no water damage, no dents, no bends in the case etc. I’m guessing that, if the motherboard isn’t destroyed, a replacement of part of the backlight circuitry is in order; I have been wanting a BGA rework station and microsoldering kit for some time (there is no way I can get someone else to fix it as I’m in New Zealand so noone does this for iPhones here). Thank you for advice on further testing - and let me know if you know of anyone has had this issue - I do wonder if I have an ’exploding’ iphone which may well have caught fire if I hadn’t disconnected the battery - it is interesting that the area of overheating was not the battery, but was immediately next to the battery…..
This is a belated answer so hopefully it can be of use to folks who search for and find this question. It definitely sounds like a backlight circuit issue. Because the phone has never been opened (i.e. to install a glowing logo) and has had minimal physical damage, it could just be a random component failure. That said, the backlight circuit is along the one of the two “fault lines” of the iPhone 6Plus; one along the Touch IC area and the other along the baseband IC. These fault lines are caused by the micro-flexing of the housing over time. History has shown that a lot of these devices have failed due to issues with the circuits in these two areas.
