How to judge the HDD failure was caused by PCB or not?

Hard disk drive failures would be caused by kinds of reasons. How to judge? We can judge it from the detail problems. Now we will introduce the HDD's electric supply malfunction here.

HDD's power supply is from computer's electrical source. Connect the electrical source with the HDD PCB's power interface; the HDD can be powered up. Power line has 4 terminals. The 4 terminal are: one red line is +5V, two black lines are ground wires; one yellow line is +12V. Linear power supply changes the electrocircuit to be the varying voltage for HDD normal working.

If the HDD's power supply has the problem, the HDD will not work. The symptoms are: no power; can't recognized; can't spin; heads do not seek, etc. The power supply's problems are always from socket terminal, filter capacitors, diodes, transistors, MOSFETs, inductors, resistors and insurance resistance, etc. Hard drive PCB components

If the power supply is unstable, sudden high voltage will burn the HDD PCB. However, the PCB has the protector: electric resistance or diodes. When the HDD suffer the abnormal voltage, the insurance resistance /protection diodes will be burnt first. Then the power will be cut off, and thereby protect the other parts of the HDD.

When the HDD encounters the voltage exceeds a certain limit, the protection diodes will be burnt. Then the HDD can't get the power supply.

2.5" HDD don't have the protection diodes; however, it has an insurance resistance which has the same function as protection diodes. When the voltage is high, the insurance resistance will be burnt and protect the HDD.