What happens when they start releasing 'magic smoke' ....
That's what causes them to stop working. The "magic smoke" is let out. Sometimes a bigger fuse isn't the answer.
When it's not the computer,
and it's not a sensor or other input device,
it can be, that the power supply voltage is off, making the 5 volts or 12 volts, whichever applies, below threshold, where it's seen as a "0" instead of a "1", causing weird, intermittent, and sometimes unpredictable problems. This sometimes happens, when the power supply is also the battery charger, and the charging voltage is wrong from maladjustment or a cell in a battery is shorted, drawing enough current to cause a voltage drop.
Some or none of this may apply to QZ8501, but might be why switching out an FAC might not have remedied the problem (assuming the reports of maintenance issues with that system on that particular aircraft have any truth to them).