First helium-filled drive for me.
The customer said that the drive dropped.
The drive spin and calibrate normally with full ID,SN, FW and caacity.
But no UA access and all sectors shows UNC.
I think it's a weak/bad head issue.

Anyway, I told the customer that I can't help in such case and he needs to contact a more experienced DR company.

If you isolate the HDA, does the drive still ID?

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A backup a day keeps DR away.

Didn't try to isolate the HDA.
I gave the drive to the customer before even unscrew the PCB.

I suspect that your drive may support Rebuild Assist. Rebuild Assist allows the user to test the heads and to skip over any LBA which belongs to a faulty head. That said, @maximus investigated this ATA command and found that its implementation was broken. In any case the drive may not respond to this command in its current state.

_________________
A backup a day keeps DR away.