MID-725 3G Service and Repair Manual CPU:RK2918 DDR：DDRⅢ256M*4 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 open 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 not. 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 not 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 level. 6. Shows that poor Check the screen is good or not, and whether a row row line normal connection. Check the U6 power supply is normal, and control line is connected to normal 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.