Malfunction Phenomenon
The phone can’t recognize the SIM card.
Trouble Shooting
For the iPhone X No SIM Card Detected issue. Take apart the phone and run the cosmetic inspection of the motherboard, and it’s a little bit deformed.
Then we can measure the SIM card connector J_SIM_K, the measured diode value of pin J_ SIM_K_2 is OL, which is abnormal.
From the circuit and bitmap, pin 8 of SIM card connector J_DEBUG_K is connected with pin F18 of U_BB_K by way of R1615.
Then measured diode value of pin 8 on J_DEBUG_K is 620, which is normal.
So we can conclude that the line is disconnected between J_DEBUG_K and J_ SIM_K_2.
We can reconnect it with a jumper wire from Pin 8 of J_DEBUG_K to pin 2 of J_ SIM_K_2.
After finished it, then make the upper layer and lower layer solder together, and assemble it and test again, problem resolved.
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