At power ON drive does not spin and flebily noises 'gn' ... 'gn'... so if motor is seized - but is not.
removed heads motor can spin without any problem manually.
already diagnose PCB and HEADS, they are OK.
resistence on wires looks fine so i would say OHM OK
since have spacer looking for a workaround before platter transplant,
if must be done will be done but you know what i mean

Check if the spindle rotates freely by himself when receives power, instead of checking only by hand.

Do not even start rotate

If PCB and Heads are tested, so the only chance is damaged spindle.

Another option to platter swap is swap the spindle.

Platters swapped, but motor still does not rotate and same noises

So... not a spindle issue... another good conclusion to mess things up

Something not adding up. It seems like the spinning problem carries over where ever the platters go and the platters should have nothing to do with it. WTH?

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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

So spindle issue is out of question.

I had a case where ROM was the problem.

Another pcb already tested so not rom related.

How did you test PCB ?

Hard drive under recovering problem fixed (after platter swap i badly re-assembly heads and released them near but not exactly in their resting zone causing a micro-stiction )
to say that motor in .12 is not powerful.

Nice

SEMPRE controllare due volte quando riassembli lo stack ! E' andata bene perche' poteva succedere di peggio alla partenza.

ALWAYS double check when reassemblying the stack. Everything went well, at startup a catastrophical event could have happened.

This is the kind of risk that is involved in DIY and is why we discourage users to attempt a DIY recovery themselves. IT really does pay to double check and even triple check!