Baseband Common Malfunction - FLY MC165 Maintenance Instruction

3.4 Baseband common malfunction

3.4.1 Nor Flash programming does not download
Data lines used for downloading software: VBAT, TX, RX, GND, CHARGE. It is
mostly due to the false solder and wire bonding. First check whether the serial port
of PC and cell phone is unrestricted, if not, it is caused by being lack of devices or
empty solder of power manager, USB-con and peripheral resistance. Measure the
TX, RX signals by using AC-coupled oscilloscope to track the signal flow, if a
certain period circuit of no signal it may be AC short circuit to ground, or is caused
by a short circuit and open circuit. On checking the malfunctions, first should
carefully observed the welding of these devices with a magnifying glass, then plug
in the download line to observe whether the current is normal, there is short-circuit
to ground of VCHG or VBAT if the current is large, at this time cut off power supply
as soon as possible, and then find the short-circuit point. It may be the abnormal
output power supply of a certain circuit that the current is larger than normal
(about 30 mA) but not particularly large, at this time should check whethe the
valgate of VCORE (1.8V), VDD (2.8V), VADD (2.8 V), VTCXO (2.8V), VRTC
(1.5V), VMEM (2.8V) is noamal, if not, bad welding can be detected. Focus on
checking the welding of PMU and USB-CON if there is a little or no current.
Unplug and re-plug the download line to see if it is caused by poor contact; It can
test that whether the output of 26MHz clock signal to the CPU is normal by using
oscilloscope.