What is this chip and why should I replace it?
It's the EEPROM that stores the drive's characteristics and specific
configuration-data which is different for each drive (even for drives
from the same batch and even succeeding serial-numbers).
For the heads, I am pretty sure that they are defective.
Have you (or "The owner") dropped it onto a concrete floor?
Opened the drive and inspected the heads under a microscope?
You can never be certain, before actually having diagnosed a problem;
it could even be that the PCB isn't defective after all.
All you told us so far is that you want to replace the PCB with another
one you found on the internet.
You haven't told us what you've done to come to the conclusion the drive
in question is defective.
Something tells me you only detected that the drive doesn't work (as it
should) and you're only guessing what the actual problem is, without any
substantiating evidence, which isn't an approach an engineer would take.