According to the phenomenon of the fault, the fault may be judged in the power supply circuit and the on / off control circuit. Open the right machine shell, a circuit board, according to the real machine draw out the local power supply circuit as shown in figure 1. Check the power switch button to switch to normal. Battery to power the machine, open power switch in the road test, with a multimeter to measure the battery and the circuit ban interface (AO935 board), (10) to (14) pin voltage to 7.8v, normal, measured 7.8v insurance resistance IP1001 end voltage. At the other end for ov, apparently not. Take down the battery, with the use of the table test, found that the insurance resistance IP1001 has been broken. Replace the resistance, restart, the machine is still no response, so the detection of power control circuit. Measuring boot control switch QR1001 emitter to 7.8v collector for the OV should normally be 7.6v test base for the OV should normally be 7.OV obviously the pipe work abnormal, that QR1001 does not have working conditions (circuit shown in Figure). Measured for 47 K normal; measured another control tube launching QR1OO2 UN921F electrode is connected to the ground, the collector for ov, base 0.4V QR1001 base resistance of R1001, voltage significantly lower (boot normal voltage is 3.3V). QR1OO2 base voltage from the CPU controls the starting circuit, the hanging at the base of the QR1OO2, reboot, measure the spot weld voltage 3.4V, indicating that the CPU has an output voltage for starting up, but QR1002 did not work, analysis of the tube may be damaged. Remove the transistor QR1OO2, with the use of the table test, confirmed that it has been damaged, which shows that the QR1OO2 damage caused by QR1001 does not work. With the same type of transistor will be replaced after the boot, the machine is back to normal, the indicators are good. Analysis of the above reasons of failure may be to replace the battery after the power of the transient current is too large, resulting in damage to the above elements.