1. Abnormal startup line: use external power supply to supply power, and observe the change of ammeter. If the ammeter doesn't respond, it's usually that the boot cable is broken or the boot key is broken.

2. Abnormal battery power supply circuit: Power is supplied by battery power supply or external interface power supply to distinguish the fault range and determine whether the electronic switch is normal.

3. Abnormal power IC: Test the peripheral circuit of power IC against the circuit schematic diagram to see if the test value is normal.

4. Abnormal system clock and reset: measure CPU power with a dual-trace oscilloscope and reset all the way to see if the measured reset time waveform is correct.

5. Abnormal logic circuit: Generally, repairing or re-soldering these chips can solve most problems. If it still cannot be turned on, the peripheral circuits should be measured one by one and these chips should be replaced.

6. Software abnormality: replace normal chip, version or rewrite software.