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MID-725 3G Service and Repair Manual
Voltage of USB:5.0V
Power supply for the system:VCC 3.30V、VDD 1.30V、VCCDR 1.5V、VDD12
1.20V、VCC25 2.50V
DDR3 power supply:1.50V
Voltage of battery:4.20V
Common fault and analysis
1. No disk, unable to identify the USB devices
Check the USB power supply is normal, + 5 V test point whether voltage
Check the usb check whether normal, often about 2.10 V.
Check the USB two data and control whether unicom. USB-DP USB-DM
two data cables.
Measuring the power supply system.
Check whether the crystal shock.
VDD_USB check the power supply is normal or not.
Check the reset voltage is normal or not. About 3.2 V
2. Update not available
Check the power supply is normal system, check DDR1.5 V power supply is
normal or not. Check whether the main control and DDR3 false welding or
IDB failure, download firmware failed, calibration firmware failed
Check the CPU and FLASH line is normal, FLASH the power supply is
normal or not. Have no false welding. FLASH data with no feet CPU op
en and FLASH without damage.
Upgrades to no disk
Check the CPU power supply is normal, DDR voltage normal, DDR and control
circuit is normal
Not produce false welding. I2C0 data feet normal, no short circuit. And normal
VCC voltage. I2C0 plug-in all the IC power supply to normal.
Test FLASH program right. And FLASH is good.
Measuring 24 M crystal frequency normal.
3. Cannot start
Check whether the OK button. If the battery voltage measurement in 3.70 V
between 4.20 and V. Check whether the D12 burn out. PWR_EN press the
button is whether feet 3.2 V voltage
Check the CPU power supply is normal, the system voltage is normal or
USB connection to test if a current. If the normal working current is check
whether the backlit fault.
4. Not even the WIFI and bluetooth
This machine is of WIFI and bluetooth integration in a module.
First check WIFI module power supply is normal or not.
Inspection module and control line is pathways. Main control signal to feet
and WIFI module of between resistance measurements.
Check modules of the 25 M crystal is working.
Check whether the inductance of the module L702 damage
5. Not even the HDMI
Check the HDMI sockets for damage and check the HDMI sockets and
HDMI IC line normal, measurement HDMIIC7150 power supply is normal or
Check 7150 IC data communication and control line is normal. Check the
connection between the exclusion for damage.
When HDMI when insertion 7150 IC to check. HPD when insertion high
6. Shows that poor
Check the screen is good or not, and whether a row row line normal
Check the U6 power supply is normal, and control line is connected to
Measuring the internal power supply screen is normal or not
The screen VGH VGL voltage is normal or not
Check whether the HDMI even tin, and HDMI display lines and screen is
the same master public, will influence each other
6. Not even the 3 G
Check module power supply is normal or not.
Check for 3 G module and control communications is normal or not. Check
the SIM card and module is normal attachment. Measuring whether ESD
short circuit.
Check the common-mode inductor is damaged or false welding
Check whether the antenna short circuit or little pieces, damage.
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