Is it possible to recover 7200.12 drive with faulty ROM chip and no backup? Only ROM chip is bad, otherwise PCB is working fine when tested on donor drive with donor ROM chip swapped.

PCB working with another drive's ROM confirms that the PCB is good, but does not confirm that the ROM is bad. What kind of tools do you have for diagnosing the drive? What are the symptoms of the drive? Do you have any terminal output from the drive for us to review?

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Luke
Recovery Force Data Recovery

When drive connected with original original PCB with ROM chip, Spindle motor does not start and when I replace ROM from donor PCB of Seagate drive , spindle starts . This clearly shows that ROM chip is short.In that case there could not be any terminal message.

more likely the smooth chip is at fault

swap it over and it should work again

My friend, please read this carefully. I have written That when I replace ROM chip , PCB starts working, Then how the smooth can be bad.

Did u try to place rom into a soic8 reader? playing with settings of latency to try to read it?

Yep, my advice first of all is to read ROM in a programmer and check it.