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damaged, otherwise need to be replaced and repaired.
b)
Under the circumstance that DJ1 has 9V, U2's PIN3 can output 5V. If it still cannot be repaired after
welding, U2 has been damaged and needed to be replaced.
c)
Use a multimeter to measure whether the voltage of 3.3V and 5V is short with the ground. If short,
cut the line and check the location of short circuit.
d)
Determine whether U1 can output 3.3V, check whether PIN5 has 3.3V, if not, then replace the chip.
e)
Check whether there is 3.3V at both ends of L4 to determine whether there is virtual welding or
damage.
f)
Determine whether U31 can output 3.3V, check whether PIN2 has 3.3V, if not, then replace the
chip.
g)
Check whether there is 3.3V at both ends of L12 to determine whether there is virtual welding or
damage.
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