My experience also shows that the vast majorities of control boards failures are in the order shown below. As you can see, the microprocessor is the least likely to cause the failure.
1- Programing errors.
2- Design error: Not including the type of protections needed to recover from adverse events : power glitches, em pulses, over-temperature...
3- Not enough IO protections that allow external over-voltages to reach the control logic.
4- Weak electronic design: Bad power supply or board design and as in #3 bad IO.
5- I have rarely seen a processor itself being affected by noise when the above is covered but it can happen.
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