7200.11 ST3750330AS def. heads / nasty FW fuckup

[Overflo]

P/N: 9BX156-568
FW: SD35
DATE: 08315
SITE: AMKSPR

drive spins up, heads start knocking.
after ~30 seconds drive shows READY.
when trying to access data i get ABR/UNC

when connecting to terminal ctrl+Z ->F3>
/1 ->OK
N1 -> LED000000....

i tested pcb 100% ok

P/N: 9BX156-302
DATE: 08213
FW: SD04
SITE: AMKSPR

heads from customer do not work in sparepart but look ok under microscope
heads from spare do not work in customer drive making typical incompatible knockknock sounds

questions:
- when looking for matching replacement heads what is a MUST to match in 7200.11 series?
- bug might also be a nasty form of firmware fuckup.
i tried the usual bugfixes by hand but they dont work as heads seem not to read

F3 T> .
Current R/W User LBA 00000000 LLL CHS 00000000.0.0000 PLP CHS 00000000.0.0000
R/W Status 1 R/W Error 00000080 Not Ready

best regards
-flo

[Overflo]

i was able to come up with a working solution.
the heads were in fact defective and i had to swap them with a matching sparepart.
the sparepart i used was from a different family 7200.11 GT series
it was manufactured 8 months later.
it was from a different manufacture site.

the serial from the customer is 3QK07QY8
the serial from the spare is 5QK0MWM2
the part number is IDENTICAL from the first to the last digit

can someone tell me if the serialnumber was of any importance here or if it was just the identical partnumber that made the heads match?

best regards
-flo