Did you put the heads from each of the parts back on their own parts and tested? I am curious if any of them are still working.

_________________
Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

The problem is that after working as described for few minutes:
"Interface task reset
4096k x 16 buffer detected
MLITE - 1_Disk M-28 03-
Buzz - 15-05 20:16
Head Mask FFFF - Switch to full int.
Spin Ready
Error Reading Boot Adaptives
(
F>"

They were gone again, doing the busy noise and:
"Head Mask FFFF Head Mask FFFF Head Mask FFFF ....."
So i assume they touched some bad area and died.

I am not sure you understood my question or I am misinterpreting your answer.

First, if after every time you did a head exchange and tested the customer's drive and get repetitive "Head Mask" messages in terminal, then the drive cannot be considered to have "worked".

I am not concerned with what the customer's drive is doing.

What I would like to know if you placed each head stack belonging to the parts back on the part drives and tested them. Are the part drives working, as in initializing and able to read SA successfully and can read LBAs? If they are not "working", then what kind of messages do you get in the terminal for each?

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

Hi mate, i'll clarify the issue:
After doing what i believe to be a successful head replacement, the patient drive wasn't buzzing as usually with bad heads and gave the following terminal message:
"Interface task reset
4096k x 16 buffer detected
MLITE - 1_Disk M-28 03-
Buzz - 15-05 20:16
Head Mask FFFF - Switch to full int.
Spin Ready
Error Reading Boot Adaptives
(
F>"

Then i tried to inject firmware to RAM using SD Segate Doctor, it tried to load for few minutes and then it seems like the heads were gone again like they reached a "dirty" platter zone:
"4096k x 16 buffer detected
MLITE - 1_Disk M-28 03-
Buzz - 15-05 20:16
Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF - Head Mask FFFF....."

At this stage the drive was buzzing and seems likes the heads were gone again.
Same happened in both "successful" heads replacements. It seems like every time it gets to some area on the platters they becomes faulty again.

At this stage I haven't tried to put the heads back to the original donor drive as i assumed they were gone, but maybe i'll try to do so and update you.

Cheers

It seems like media damage to me.

The reason I was asking is because upon placing the heads back on the parts and testing, then it can provide you a little more insight toward concluding what the problem is.

_________________
Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

you are right, i am pretty sure that there is a platter damage.
I may try to replace the heads back to the donor but i am quite sure they are dead.
Thx