c. After eliminating software and battery problems, check whether the battery connector is welded well and
whether there is desoldering;
d. Check the power-on circuit
5.8 Not charging
a. Check whether the battery voltage is lower than 6V. If the battery voltage is too low, it will not charge;
b. Check whether the charger, data cable and USB interface are in good condition;
C. Check the relevant charging circuit.
5.9 Unable to recognize SIM card
a. Check whether the metal surface of the SIM card is oxidized or has foreign matter;
b. Check whether the elastic feet of the card holder are in good condition;
c. Check whether the pins of the card holder are soldered;
d. Check related card circuits, TVS, and chips.
5.10 No network, weak signal
a. Check whether the motherboard antenna is assembled well;
b. Check the welding condition of the antenna shrapnel;
c. Check whether the RCL component of the mainboard RF antenna shrapnel has fallen off;
d. Check the RF circuit of the motherboard
5.11 Unable to print
a. Check whether the printer connector cable is connected properly;
b. Cross-check whether the print head is damaged;
c. Check whether the printer motor driver is hot. If so, replace the driver chip and check TVS;
d. Check whether the printer MCU is damaged, and if so, replace the MCU;
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