I recently had a power surge in my PC and two of my hard drives now do not power on. They are both 2TB WD20EARS. I have read about how simply replacing one of the diodes could be a easy fix, and bought a multimeter to test them before I removed them. I thought I understood what I was doing, and removed the D4 diode in one of the hard drives. It still will not power on.

I have a third WD20EARS in a WD external enclosure. I tried this hard drive's PCB on the two HDD's that would not power on, and they do indeed power on with this PCB, though of course not detected by my PC.

Any help would be appreciated, thanks.

Hi, can you see any burn signs on both PCBs?

There are 2 TVS diodes on this pcb near to sata power supply connector (5V line and 12V line), i have marked them with a red circle.
Check those two TVS diodes with diodes tester of your multimeter in both direction, if they are shorted then remove them and see if drive spins.
Check also those two "0 ohm" resistors that i have marked with orange circle, if they are open then it's better to change directly the pcb with donor pcb (in this case you have to do the rom transfer job)

If diodes are shorted and you remove them then the drive should spin unless there are other issue (example with those "0 ohm" resistor or with the VCM controller chip), if still doesn't spin it's better to change pcb + rom transfer (not DIY job).

If data are important i suggest you to let do this job to a pro.

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My firmware database:
https://mega.nz/folder/O01DkBRI

If the surge hit the +12V supply rather than the +5V, then there is a very good chance that a PCB swap should get you going again, but you'll need to transfer the 8-pin chip at U12 (if it exists) from patient to donor.

A PCB + firmware transfer should cost you no more than US$50:

http://search.store.yahoo.net/yhst-4446 ... ion.com%2F
http://search.store.yahoo.net/yhst-1443 ... rts.com%2F

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A backup a day keeps DR away.