Paul wrote:

VanguardLH wrote:

https://www.hddzone.com/fix_hard_drive_pcb_board.html

https://www.youtube.com/watch?v=Yn2eL4o-6Eo
Timemark 5:40 - Swap doesn't work.
Timemark 7:12 - Gotta swap the ROM chip.

You'll end up having to move the ROM chip, if still usabled, from the
failed drive's PCB to the identical replacement PCB. ...

According to this, the main chip has firmware.

Yes, some microcontrollers chips have a ROM section. The Youtube guy
mentioned that. Instead of transplanting a ROM chip, you have to
transplant the microcontroller chip assuming the PCBs are clones so the
surrounding logic is the same.

Knowing all the architectures used in different brands, models, and
submodels, especially since some same-brand drives come from different
factories can make you go crazy. Some have separate ROM chips. Some
have ROM inside the microcontroller chip. The point was that the drive
data on one PCB may not be usable or be incorrect for another drive.