BR1000MS F02 error - no prior warning - iMac now DEAD

[eiseman]

In 2020 we purchased a couple of BR1000MS to provide back up for an OLD 27 Inch iMac and a newer 27 Inch iMac from 2019

Everything has been satisfactory until this morning when a piercing noise erupted from the unit connected to the OLD iMac. Initially I couldn't tell where that piercing shrill originated. I thought it was a carbon monoxide sensor but then found it was the unit which was displaying "F02".

I pressed the button to turn it off and went to check fuses outside. Nothing had tripped so I came back in and restarted the unit. It came up normally and displayed 116V (default if I am correct). 

I subsequently disconnected everything except the internal battery after it resumed "normal" operation.

It seemed like everything was back to normal but, apparently, whatever happened fried the OLD iMac.

It will not boot. It was in need of replacement and is absolutely necessary for the day to day usage of the owner. So we have a new one arriving tomorrow.

So this event makes me VERY apprehensive about connecting another iMac to it.

Does anyone have any idea if this BR1000MS is fit for duty or a way to check?