Malfunction Phenomenon
There is no signal when the phone is being used
Trouble Shooting
For the iPhone X No Signal Issue. As the same, the first step we will take apart the phone and run the cosmetic inspection of the motherboard.
After checking, the cosmetic is OK, then detach the two layers of the motherboard from each other and remove the SIM card connector and measure the power supply of the RF circuit. We found that the diode value of VDD_RFFE_VIO_1V8_K is smaller than normal. So we can confirm that the fault is related to VDD_RFFE_VIO_1V8_K.
There are too many relevant components on VDD_RFFE_VIO_1V8_K. We can check and locate the abnormal component by touching with the finger, thermal camera, or rosin inspection method.
Finally, we find the MHB PA is hot when touching the relevant circuit with the finger. So we can conclude that the fault is related to MHBPA_K IC.
So we replace the chip with a new one and put back the SIM card connector after that put back the middle frame and make the upper layer and lower layer solder together.
Then assemble it and test again, the problem resolved.
