[Xiaomi Mi 5 Questions & Answers] kanoc39606:
EDIT(After 2 weeks)TEMPORARY SOLUTION WORKED FOR A WHILE BUT as imauri1990 mentioned in his post, it is mostly related to cracked solders. The solder material looks like balls(0.12mm) and located under RAM which can be SEC612 or SKyhnix. I think sec612 is 4gb ram, SKhynix is 3gm Ram ic. Under the RAM there is another chip(CPU i think), this chip can also have cracked solders.

- Why this happens?

I dropped my phone so bad, my screen protector is broken and my battery is a little bit swollen. Some guys who sell their phone on a website(used phones), i read all their posts and they almost say same thing, some of them dropped, some of them sit on it. After that their phone is not being started or touch is not working. This shows us solders are broken or cracked.

- Sympthoms:

1- My touch screen was working randomly. If i press on top middle part of screen( close to 2-3 cm below from camera) my touch screen was starting to work, if it does not, i double press power button or restart the phone than it was randomly starting to work.

2- My phone was closing itself randomly and not working even i press power button. I almost unscrewed my phone about 50 times and was removing the battery connector, pressing power button 10seconds, after i connect the battery connector the phone starts to work. When phone randomly close itself, it consumes so much energyt and battery is being discharged so fast. After sometimes the reconnecting the battery socket started not working, if i press the back of the motherboard or if i twist the phone holding with corners it was working randomly, also twisting was working as a solution for non-responsive touch screen. When phone is closed without reconnecting the battery, i tried charging the phone with using a usb-tester device and it was consuming 0.02Ampere and 5volts. Tried with fast charger and normal charger but it sometimes was charging 0.42 A if i twist the phone and not reconnect the battery.

I watched this video and after reading previous post (imauri1990), i thought the problem is about CPU and RAM ic solder cracks. Because under my press point there was RAM and CPU. It was faulty with a high probability. Also I watched lots of mi5 touch screen or repair videos some indonesian, russian technicians was reballing these ICs.

- Interesting:

I have never seen two BGA chip soldered top of another and top of motherboard. When imauri1990 said "heat both Cpu and Ram and show a red rectangle on his image, i thought "where can be the CPU?". Never thought cpu was under the RAM :ROFLMAO:

- SOLUTIONS:

1- If you have only hot air station:

You can try heating the RAM only, after heating(370 degree hot, %42 air output) you can test your device. Be careful about not moving the RAM with tweezers while heating. In my case, i watched videos and moved the Skyhnix RAM ic with tweezers in order to fix cracks and solder it better but some pins under the RAM bonded, shorted.

2- If you have hot air station and Stencil(Amaoe MI-8 stencil) And NOT SKILLED on BGA-Reballing

If first method not worked, you can buy a Amaoe MI8 stencil that may seems like specific to mi8 phones but nah, this is the part number of Amaoe brand made for mi5/mi5s/mi5s plus/Note2/MIX. You may only remove RAM and reball it. You should also heat the CPU that is located under ram to fix the cracks without reballing. (I usually used 340 - 370celcius degree and %42 air rate with a high quality liquid flux). You can watch this video for how to reball the RAM IC. When i tried reballing without watching this video, i lost 4 hours of my time, never succeed even i try lots of method and locally reball the RAM. Becaause even i was skilled on soldering any compenent on a board, i have not done any BGA reballing. Also the stencil is being wrapped while you heat the flux mixture o_O. If you put excessive liquid flux+solder paste mixture on stencil and not clean excessive part, the balls looks like mushroom and if you try to pull back the IC under stencil, the pads are lost and happy for you, you should buy a new phone!

But you can use lancet or falchta to cut the head of mushroom styled balls on stencil but never do this please, just clean the excessive part carefully and so clean. After reballing, you may need reball some missing parts again, carefully watch the video, same technique and starting from same point with the same position also same tweezer holding method, this is really worked after 1 hour. In my case this method is worked, because i am afraid of reballing the CPU, because it has lots of balls on it.

3- If you have hot air station and Stencil(Amaoe MI-8 stencil) And very SKILLED on BGA-Reballing

Just do your job, you are the master. Reball and resolder RAM and CPU.

- Notes:

I used original mi5 charger, my usb tester was showing me variable currents and voltages over time like two seconds. 6.23V 2.43A, 6.3V 1.9A then going down to 6.1V 0.40 ampere. After that it was increasing like 6.3V 2.3A then again drops. I thought there can be some solder cracks on power IC so just only reheated it which is shown in this video. I didnt changed it. After repairing process, the usb-tester shows that the Ampere value didn't changed so much, it dropped down while the battery arises up to %100 after %80 charge. This is normal for battery health while charging it.

Use high quality flux and flux-solder paste. I didnt mention about cleaning process or flux stuffs but you can watch videos. Never drop flux-solder paste to your motherboard, i did this mistake and after heating the motherboard the paste soldered some pins.

If you use hot air station with a high flow rate more than %50, your small components may go to another places randomly and I dont wanna imagine your face when it happens. Also use 300-370 celcius degree. Not more!

I hope you can repiar your lovely phone and use it or save your data. Firstly thanks to God! After thanks for your posts, if you didnt share your experience, I might not have any idea. Therefore, i am wrote this with spending my life about an hour. (y)

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