We’ve a case with the following HDD:

Fujitsu MHW2120BH with PCB dead.

We have a donor exactly the same model.

1.) We’ve swapped the PCB patient with the PCB donor. The HDD run but not initialize. It’s not detected.
2.) We’ve swapped the HSA patient with the HSA donor. This is the same thing.

Do we need to unsolder the PCB rom chip patient and solder it on the PCB donor ?

Thank you in advance for your answer.

Yes. But check fuse on bad PCB first.

Thanks.
I've read that for this family HDD (Fujitsu MHW) there isn't any rom chip but bga chip.
Is this bga chip contain unique informations for each HDD as a nvram for hitachi ?

Yes, masked ROM is contained in big chip. Not a soldering job for the faint-hearted. Did you check the fuse as I suggested previously?