I really think you need to be fixing the patient board.

Assuming the motor IC is the same - why not remove it from the patient check for a short, replace it with the donor and check for a short.

_________________
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https://www.usbrecovery.co.uk/

Did you ever resolve your issue?
I am experiencing precisely the same symptoms - no spin.
I have gone over my board referencing each post in this thread and voltages at all test points are identical to the patient board referenced here.

Just FYI, the dual e-fuse on the OP's PCB is an MP5094. It is pin compatible with the STEF512.

MP5094, Monolithic Power, Dual-Channel 12V/5V Current-Limit Switch with Output Over-Voltage Clamp, marking AYUy, TSOT23-8:
https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP5094/

Is it possible that SATA power pin #3 was supplied with 12V rather than 3.3V? This is the DevSleep pin. I think it is connected to the MCU. I would measure the voltage on this pin.

_________________
A backup a day keeps DR away.

Sata Pins 1-3 all measure 0V. But, I also tested several Sata adapters I have here and they all do not provide 3.3V on pins 1-3. The do provide 5V on 7-9 and 12V on 13-15

If you connect the PCB on its own, do you see any sign of it in BIOS or Disk Management or Device Manager?

If you slip a business card between the PCB and the HDA pads, does the drive spin up?

_________________
A backup a day keeps DR away.

The board alone inserted in a Kingwin adapter does show up as /dev/sdc in linux

root@TR-DR-2:/home/tr# lshw -C disk
*-disk
description: SCSI Disk
product: EZD-2537U3
vendor: KINGWIN
physical id: 0.0.0
bus info: scsi@6:0.0.0
logical name: /dev/sdc
configuration: logicalsectorsize=512 sectorsize=512

But, it does not show up when connected to an eSata port I commonly use.

And, it does not spin up when the 22 pin HDA connector is insulated.
No voltage on the 4 motor pins either.

I noticed that the OP was using a donor board with one BIOS chip instead of three and wonder if that affected his results.
I have ordered the correct donor board due to arrive in a few weeks from China.

When connected via USB, the OS is seeing the USB-SATA bridge firmware, but not the HDD behind the bridge.

The OP's PCB was able to report the model number via SATA, so that would suggest that your board's MCU is not responsive.

_________________
A backup a day keeps DR away.

I understood that you wanted me to report behavior with board disconnected from the drive. I think the OP was giving results of the board and drive unit together because he was saying that the drive did not spin.

Yes, maybe I misunderstood. I'm not so sure now. You could always try this with your replacement PCB when it arrives.

_________________
A backup a day keeps DR away.

So, I just received a donor board today, transferred the three bios chips and there was no change.
The drive is still completely NSOL.

Seems like our boards have been good all along and maybe the motor is blown?

You can check if it's blown via the windings.

_________________
Data Recovery Services in the UK.
https://www.usbrecovery.co.uk/

Did you try the donor PCB before you transferred the ROMs?

_________________
A backup a day keeps DR away.

I did not, but I will, and report back.

How would I do that?
I do not have an ISO room but I do have a very clean environment ( ) and have opened up many drives without dust issues to do head swaps and even a few successful platter swaps.
My main obstacle is that I have to wear a mask so I don't drool on the platters when working .

The spin motor has 3 windings ("phases"). Measure the phase-to-phase and phase-to-common resistances using the 200 ohms range of your multimeter. They should be around 2 ohms and 1 ohm, respectively.

_________________
A backup a day keeps DR away.

How - is as per fzabkar's instructions, Where - is from the outside of the drive where the motor contacts for the pcb are.

_________________
Data Recovery Services in the UK.
https://www.usbrecovery.co.uk/

Did you guys solve it?

I have a similar issue as OP on the same board, though with different components (eg. I dont have electronic fusem, only have 1 ROM IC and all my inductors look like inductors -- ie. have uniform casing).
In my case the fault was most likely caused by multiple failures -- first a voltage spike, followed by a short and 12V supplied to the 5V rail (don't ask how, don't ask why ).
The 5V fuse was fried and the TVS was shorting the 5V rail to GND. I've replaced the fuse, TVS, and protection diode (it looked fine on the DMM, but I figured I might as well replace it anyway).

Still, the motor won't spin and the head won't move, but I see 200 mA being drawn on the 5V rail (constantly). I don't know if any current is drawn from the 12V rail because I have only one bench supply, and thus 12V is coming from a non-digital power supply (genuine MeanWell, so I hope it doesn't botch the results). I don't see any components heating up more than the motor IC itself (alongside the other "main" IC), to around 40°C.

I took some measurements (perhaps more than I should), but I figured it's better to take more than too few.
At this moment, I've reached a ceiling and I don't know how to move further.

I won't buy a replacement board because I don't care about the data on this drive -- I'm doing this purely for curiosity and the potential satisfaction of not having to throw this drive into a landfill!

Can you tell us whether the preamp supplies are present? Many designs will switch on the negative supply briefly after power-up and then switch it off if the preamp is not detected. If this doesn't happen, then this would suggest that the MCU and motor controller are not communicating.

Can you verify whether the test point at the MCU is connected to either Vp1 or Vp2?

Edit:

I'm not sure which side of the Vp1 capacitor is grounded, so you might test both ends.

_________________
A backup a day keeps DR away.

So vp2 is ~5V and vp1 is ~0V. Can't tell if these values are expected so I'm just posting numbers and an updated image. I've also took the liberty of marking them with separate colours and an zoomed in section around these components.

1) The part between 4.9V and 9.75V is an inductor? I wonder what account sfor this voltage split in half on both ends, while all other inductors show output voltage on both ends. I assume this may have sth to do with me measuring it with DMM instead of scope?
2) You asked to test endpoints between MCU (I guess you meant the IC in the middle - motor controller?), not the IC on the right (with thermal pad)?

in any case I couldn't find path from either vp1 or vp2 to the IC with thermal pad test points. The ones I've found were close to the IC in the middle, however I'm not sure if they are connected to the IC itself or only in close vicinity.
Sorry if I missed something