Request for Help with Overvolted WD Reds

I’m reaching out for help or insight from anyone who’s dealt with similar issues. I recently encountered a serious problem with several Western Digital Red NAS drives (4TB, model WD40EFRX), which may have been overvolted due to a faulty power supply setup. I’d really appreciate any advice or confirmation on symptoms and possible recovery options.

Background:

I’ve been running a small home NAS server with five WD Red drives in a RAID 5 array via a Synology DS1520+. Everything was stable for over a year. However, last week, I attempted to relocate the NAS into a new rack-mounted UPS + PDU setup. The moment I powered on the unit in its new configuration, something was off.

Two drives didn’t spin up, and the NAS began throwing SMART errors on the remaining three. I immediately shut everything down and isolated the drives.

What Happened:

After some investigation, I realized the power strip connected to the PDU might’ve been delivering overvoltage. It was a cheap unregulated unit, and I suspect it passed through 15-16V on the 12V rail, possibly more during boot surges. I’ve since replaced it with a voltage-stabilized APC unit, but the damage may already be done.

Symptoms:

Two drives are completely dead. No spin-up, no sound, not detected via SATA dock or directly to motherboard.

Three drives do spin up, but SMART status shows “Reallocated Sector Count” rising and “Pending Sector Count” not dropping even after extended reads.

All drives emit a faint electrical smell when removed, which I never noticed before.

PCB on one of the failed drives shows discoloration near the power regulator chip.

My Questions:

Is there any way to confirm if these drives were indeed damaged by overvoltage?

Can PCB swap recovery work on WD Reds, assuming I find identical donor boards?

If firmware microcode is embedded in the PCB ROM, will a simple swap even work?

Are the remaining drives safe to use after showing SMART degradation, or should I retire them immediately?

Can I expect Synology RAID parity to rebuild if I replace the dead drives with new ones?

Next Steps:

I’ve already begun backing up what I can from the remaining drives, but I’m not confident in their longevity after this incident. I have a few replacements on order, but I want to ensure I’m not introducing risk by reusing borderline drives or by misunderstanding the voltage damage.

Any advice from electrical engineers, data recovery experts, or anyone who’s been through similar overvolting would be hugely appreciated. I’m hoping I caught it early enough to recover data, but I’m bracing for the worst.