Alright so i had a ST9750420AS in a MBP 13 i got for my GF 5 months ago after 3 months the MBP froze and asked her to restart and showed the wonderfully angry question-file on startup. after testing the HDD in other devices with seatools and everything i was unable to have it seen or even spin up. i threw on the PCB off of the supposed "back-up drive" i had set up for her to use with time machine...(she of course never used it... HUZZAH!) both were the exact same harddrive i bought together thinking i could avoid having problems... now with the new PCB the drive feels like it will spin up to full speed but still will not be seen by my desktop, in an enclosure or anything. both show the same firmware version on the sticker im wondering if i just have to transfer the ROM chip from the old to the new? i dont have the old drive because she decided to send it in to seagate and use their recovery service... im looking around trying it figure out my next step while i wait for seagate to send her a quote and for her to come back to me to fix it for her... and will seagate tell me whats wrong or just say its fried we need moneyz to get your data back?

The board swap with the rom swap doesn't resolve ALL hard drive problems. We have no idea what the original failure is or was without having the drive and doing proper diagnosis which Seagate will now do and provide a quote for their services. no they won't tell you what is wrong with the drive specifically your best bet at this point to move forward with Seagate's recovery services to get the data back.

from what i can tell there seems to be an electrical fault somewhere on the PCB board since with the faulty one the harddrive will not respond at all but with the new one it will at least spin up. i do not have the knowlege on how to diagnose where the problem might lie or if it is possible to transfer the PCB board on this particular model, i have been reading the board trying to find an easy answer but have not found a definite answer of if it would repair the broken drive, i have read a lot of answers that contradict one another on the subject. i just try to DIY everything i own that breaks...

If original drive won't even spin up with original PCB, you should start there. Problem might be beyond PCB also.
Seagate won't be very specific and most likely will provide several possible failures.

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i switched to a new PCB board off the same type of hardrive same firmware and everything the drive now spins up and is seen by bios but that is as far as i can get i cannot get anything to see it after bios... is there something i have to do other than a direct swap of the board? i read alot about moving the ROM chip over but i dont want to destroy me getting an RMA by me guessing...