Redmi Note 5 can't get into the system repair

Redmi Note 5 can’t get into the system repair

Machine model: Redmi Note5
Fault symptom: turn on Restart repeatedly,no Baseband Version and no serviecs.
When this machine comes, it starts Restart repeatedly. If it doesn’t enter the second interface, the current can reach 700ma, which means that the self-test of the kit and chip is basically completed. Don’t see Xiaomi Restart repeatedly and then do the kit.

Redmi Note5 can’t get into the system repair Figure 1.

I swiped into the system and found that no Baseband Version had no WiFi.

Redmi Note5 can’t get into the system repair Figure 2.

Baseband WiFi is available after changing IF.

Redmi Note5 can’t get into the system repair Figure 3.

Redmi Note5 can’t get into the system repair Figure 4.

Card insertion found that it can read cards,no serviecs, manual operator failed.
Fault analysis:
The search operator of Qualcomm model failed, or called to remind you to turn off the flight mode and turn on ANT. The chip on RFFE Related circuit is damaged or not working properly.

Maintenance process:
At first, the VCC of power amplifier and ANT Switch were measured, and all of them were normal. Redo the two chips and the fault remains the same.

Redmi Note5 can’t get into the system repair Figure 5.
This RFFE2 bus involves three chips, including power amplifier power supply, which is disassembled and redone.

Redmi Note5 can’t get into the system repair Figure 6.

Using the traditional Hand solder to drag PAD and chip pin bits,REBALLING always feels that the tin spots are not uniform.

Redmi Note5 can’t get into the system repair Figure 7.

Manual search for operators failed, so the failure of replacing all signal chips with new ones remained.

Redmi Note5 can’t get into the system repair Figure 8.

Looking at the drawings, it is found that the bottom pin of DRX diversity receiver on IF is equipped with RFFE4 bus, which will theoretically make it impossible to search for operators, so it was disassembled and redone, and the bottom pin bus was tested to be normal.

Redmi Note5 can’t get into the system repair figure 9.

When reloading DRX, use the method of dialing tin to make every solder spot of pin full, and then observe whether ANT Switch is not installed, and some spots of Inveracious Soldering are missing.