That's scary, shouldn't the PSU take the hit if the voltage was too high/low? I don't have the knowledge required to judge this matter but I have experienced voltage spikes/drops in my farm and the result have been for the most part a dead PSU, the quality of the PSU could be the key here so make sure you confirm this matter and perhaps get a different PSU for the good unit before it's broken.

The resources on Avalon repair are almost non-existent, but here is a good telegram group https://t.me/MinerRepairChat try asking there.