FLY EZZY, Service Manual

Page: 21 / 37

Chapter 4: Failure Analysis
The main fail cases:
Fail to download; Fail to power on; Fail to make a call (due to RX or TX); Fail to charge; RX/TX
power fail; Audio malfunction; No vibration; No display; Power supply fail; SIM check fail and so on.
In mobile circuit system, all the electrical connecting trace can be divided into three types, such
As power supply trace, controlling trace and signal trace. When analyzing the RF failure case, for the
Active circuit we should first check the power supply, then control circuit followed by the signal flow
Path to remove the failure step by step. When debugging the RF malfunction, we should diagnose the
RX part first before TX.
With the help of oscilloscope we can diagnose power supply issue, control signal trouble and
Some low frequency signals, such as I/Q signal, RTC signal, crystal oscillator signal and so on. We can
Measure the signal features such as amplitude, frequency, duty cycle etc. We can also use multimeter
to measure power supply DC voltage. For RF signal, we usually use spectrum analyzer to check signal
Spectrum and amplitude in frequency domain.
We provide a useful phone maintain software - META. Some introduction about META will be
Showed below.
4.1 Analysis of base band failures
4.1.1 The handset can not be power on
Interrelated components are mainly as below: PMIC
、
Baseband chip (MT6223A),MCP Flash
，
RF
Transceiver (AD6548), 26MHZ VC TCXO, 32KHZ crystal. you can measure the 7-route LDO voltage: VCORE
（
1.8V
）、
VDD
（
2.8V
）、
VADD
（
2.8V
）、
VCTCXO
（
2.8V
）、
VRTC
（
1.5V
）、
VMEM(2.8V). Then
measure if the 26MHZ,32KHZ output the CLK signal with right frequency to baseband, if no fault occurs,
continue to check FLASH, baseband chip by download a code, if can download DA, indicate baseband is
normal, otherwise re-soldering the baseband chip and memory .replace these chips if all the step can’t solve the
fault.
4.1.2 Display failure
FLY EZZY is a bar phone, LCM is soldering on the PCB directly. A bad soldering can lead to display
Failure, you can check it with your eyes or measure the PIN with digital multimeter, if the soldering is
OK, maybe it is the problem of LCM or MAINPCBA. You can change the LCM or repair the
MAIN PCBA.