Circuit analysis:
The SIM card circuit, external SIM card is directly connected to the main chip, including SIM
card data line, clock, reset line, power line
Fault analysis and treatment process:
The boot can not find the SIM card, the card good structure, contact should be clean and
elastic line device, if short circuit, voltage is normal (Note: not in the inserted SIM card only
moment in the boot can be measured about 2.8V VSIM, multimeter some deviation, need to use
oscillograph can be more accurately measure). Check the SIM card and the PMU signal pathway
is normal, bad welding or replacement of PMU according to the.
Detection Process:
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