User:UntoK/Sample Guide

Note: This is a copy of the first problem listed in the IPhone 11 guide.

Tools and Equipment
To do this repair you will need a set of fairly advanced equipment.


 * Microsoldering capable soldering iron and hot air gun.
 * DC-powersupply
 * Freeze spray or a thermal camera

Diagnosing this fault
Connect the DC-powersupply to the phone to measure the amount of power it draws. If the device does not power on and draws over 2 Amps from the DC-powersupply then follow this guide.

Repair
Do a full visual inspection of the board and check for water damage under the stickers on the back. Remove the foam around the connectors to get a better look at everything. You're looking for any signs of corrosion on or around components and ICs.

If there is no water damage, is is most likely a shorted capacitor on any of the below lines:
 * PP_VDD_MAIN This is the most likely line to be shorted
 * PP_VDD_BOOST This line is usually shorted when it's not VDD MAIN
 * U_NFC - In some cases, the chip itself can crack & cause a short within the bottom board.
 * Rigel (U4400) This is a bit rare but it does happen

You'll need to inject voltage (4V / 2A) directly into the line you measured as short and use freeze spray (see here https://youtu.be/3MtLSQJvQxI) or thermal camera (see here: https://youtu.be/fkd4iDjgfvc) to spot the capacitor that is shorted.

In these cases, you can just remove the shorted capacitor and not replace it. The device will function normally with no negative effects.

Replacing it means you are adding more heat to the board to reinstall it, which increases the risk of something going wrong.

If you have a case of water damage, then you'll have to pay attention to the spots on the board where there's signs of water damage.

Often, you'll find corrosion on capacitors but also under ICs.

Since this is a 2 layer board, you can split the sandwich into 2 separate parts, top board & bottom board.
 * Then you can check to see if the short is still present when connecting the top layer to the DC Power Supply by itself.
 * If the short is still present, the culprit will be on the top board somewhere
 * If the short clears, then the short is present on the bottom board.
 * In this case, you can inject voltage into the bottom board to find the short.

Please Note: If you are using a DC power supply to inject voltage through the battery connector, like using an iPower Pro or DT880 (see here https://youtu.be/rawjB9yxe1A), be aware that Yangtze may heat up instantly. This is because the battery connector line PP_BATT_VCC connects to PP_VDD_MAIN through it, which creates lots of heat. In most cases, the short is not the chip itself, but a shorted cap. In rare cases, it's Yangtze itself. So try removing it & check if there's any shorts under Yangtze. If not, then the issue was Yangtze and you'll need to replace it.