hitachi very slow after heads swap

[Bunsun]

Hi everyone

I'm now practicing on hdd heads swap,what I do is taking discs with a good head maybe with few bad sectors,puts inside data, taking out the heads with professional equipment and brings them back into place then try access the data.
What happens is while in Seagate and WD always anything goes well and can access the data immediately from proper partition no software needed,but in hitachi after head replacement the disk became very slow and some times extremely slow when connect it as a second disk and some times can recover just by software some times even software failed and can see just empty partition.
I tried three 2.5" HTS545050B9A300 all of them same symptom.
I know it is possible to extract data with special equipment but first I want to understand why this phenomenon happens.
Is anyone familiar with this phenomenon ? how can I prevent it ?

Thanks all

[BlackST]

So you take heads off and put back on SAME drive (let alone swap on a patient...)

1) On OLDER WDs maybe, on most common recent if you just open the lid it won't work again . So don't say "always anything goes well".
2) On Hitachi there are other problems to consider and / or it's you damaging the headstack. A DDA can tell everything by analysing the signal before and after.