2SB1188-R, Rohm, medium power transistor, PNP, hfe = 180 to 390, −32V, −2A, 0.5W, marking BC+Rx, SOT89:
https://www.mouser.lt/datasheet/2/348/rohm_semiconductor_rohms10503-1-1742597.pdf

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A backup a day keeps DR away.

Thank you very much for reply!

When I measured transistors(QW1 and QW2) in the spare SV1021H, which works correctly, I noticed that It was measured 0.102 DCV between pin1 and largest pin, 0.784DCV between pin3 and largest pin. DC voltage between pin1 and largest pin is very different from that of working PCB.

When I compared resistance of 22uF 25V capacitor with same capacitor in the working PCB,Its resistance is very different from each other.So I desoldered this 22uf 25v capacitor and it is measured 17-18uf capacitance.As I have very little experience in smd soldering,I managed to resolder it on its soldering pad.So it looks screwed up But it seems that It did not develop a short circuit or open circuit.
When I measured resistance between motor terminal(white, blue, black circle in the below picture) all of them measured 1.1ohm.
and Its resistance is the same with motor terminal in the working PCB.
https://i.ibb.co/WxfMF6g/20241019-172559.jpg

Thank you very much for reply!
I compared resistance of the 22uf 25v capacitor with that of spare SV1021H PCB which works well.As resistance are very different from one another,So I desoldered this 22uf 25v capacitor and it was measured 17-18uf capacitance.
But I have very little experience in smd soldering,I managed to solder it to its PCB pad.
and I measured all of motor terminal in the white,blue,black circle of below picture.
they are measure 1.1 ohm in the both of problematic and working SV1021H PCB
https://i.ibb.co/K0Wf7XF/20241019-172559.jpg
And I noticed that transistors(QW1 and QW2) in the working SV1021H PCB was measured 0.103VDC(between pin1 and largest pin) and 0.737VDC(between pin3 and largest pin).It is totally different from measured voltage in the problematic SV1021H PCB.
It seems that some components which is connected to QW1 and QW3 cause abnormality(Spindle Motor won't rotated at all).

Obviously, the original motor controller is faulty. Did it fail on its own, or was the drive overvolted?

I don't understand the function of QW1 and QW2, but I'm wondering if they are connected in parallel. That is, does pin #2 of QW1 connect to pin #2 of QW2, and pin 3 to pin 3? Does the 3rd pin connect to +12V? Does the middle pin connect to the motor controller IC?

Can you measure the voltages between ground and each pin of QW1 and QW2? Do this with the working PCB. You can do these measurements with the PCB off the drive.

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A backup a day keeps DR away.

I'm a little confused about your spindle motor measurements. Normally there would be one common terminal and three phases (windings). The phase-to-phase resistance should be double the phase-to-common resistance.

Can you measure the resistance between the two pins in the HDA header, with the PCB on and off the drive? I believe these are the VCM pins.

This is a similar drive with a QW1 transistor (but not QW2):

https://wasp.kz/articles.php?article_id=1087

_________________
A backup a day keeps DR away.

Thank you very much for reply!

I'm really sorry that I finally noticed that there is two type of SV1021H which make use of different transistor(it is written "BC RF" or "SZS" on its surface) for QW1 and QW2
https://i.ibb.co/SRt7Qq5/20241022-175331.jpg
<BC RF>
https://i.ibb.co/V2t40PP/20241022-175222.jpg
<SZS>
I measured voltage of working PCB which is written "BC RF" on its surface of QW1 and QW2,It was measured 0.021VDC between pin1 and largest pin and 0.646VDC between pin3 and largest pin.
It it almost the same with voltage test of broken PCB.
and I also measured all of QW1 and QW2 transistor's pins by placing black probe on ground pin of power connector in the PCB and placing red probe on all of pins.
it was measured 2.673DCV and 2.646DCV 3.295DCV 2.645DCV for pin1,pin2,pin3,largest pin.
and It was measured almost same voltage in the working PCB which is written "BC RF" on its surface of QW1 and QW2.
I measured resistance between the two pins in the HDA header(two pins in the violet circle from your picture)
It was measured 11.8 ohm in any kind of situation(with the PCB on and off the drive and working and broken PCB).

The SZS transistor is equivalent to BC. It looks like it may be the pass transistor in a Vcore regulator, in which case Vcore would be 2.6V.

KSB1121-S, Samsung, PNP transistor, Lo-sat, -30V, -2A, 500mW, marking SZS, SOT-89:
https://www.mouser.com/datasheet/2/149/KSB1121-57411.pdf

The voice coil is not open circuit, so I think it is OK.

That said, I don't know why your replacement PCB is not spinning up the drive. Can you hear any sound if you place your ear against the drive?

I don't know whether your model has a UART port, but you could investigate it.

How to connect a terminal adaptor on a Samsung drive ?
https://www.hddoracle.com/viewtopic.php?p=432#p432

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A backup a day keeps DR away.

I'm guessing that this is the UART port.

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A backup a day keeps DR away.

I'm sorry for the delayed reply.
A few days ago, I have to pay the rent in arrear so I have been busy to borrow money for payment of overdue rent.
By the way, When I powered on broken SV1021H HDD,I placed my ears close to HDD.
And I found that It is possible to heard seldomly clicking noises from broken HDD which was usually heard just before spinning noise from ordinary HDD.
But it seems that this clicking noise won't lead to spinning up for an unknown cause.

It sounds like the drive has a stiction fault (heads stuck to platters).

_________________
A backup a day keeps DR away.

But when I swapped its broken PCB for working PCB,it surely spinning up and it was truely recognized in the computer BIOS which has PATA connector.
So I'm 100% sure that there is no stuck to platters or any type of platter failure.
By the way,I measured resistance between pin 1 and 2,pin 2 and 3,pin 3 and 4,pin 4 and 5,pin 5 and 6 of hitachi HA13626 chip, and compared it to that of working PCB.
https://i.ibb.co/KDXGcZJ/20241031-223321.jpg
I found that resistance between pin 1 and pin2(26.09k ohm for working PCB, 23ohm for broken PCB),pin5 and pin 6(13.77k ohm for woking PCB, 13.1ohm for broken PCB) was very different to each other.
and resistance between pin 2 and 3(26.09k ohm for working PCB,13.03k ohm for broken PCB),pin 3 and 4(26.09k ohm for working PCB,13.02k ohm for broken PCB) was the half of woking PCB.
I guess that hitachi HA13626 chip would have been faulty or a certain component near HA13626 chip have been broken

But earlier you wrote ...

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I'm sorry that It seems I omitted what I really swapped for.It does not means PCB Replacement
It actually means that I detached broken PCB board from hdd disk drive and attached it to another working hdd disk drive.

I noticed that the resistance between hitachi HA13626 chip's pin5 and ground pin of power connector was 1.1 ohm.So I traced PCB track of HA13626 chip's pin5,and I finally found that one of its track have been crushed which is shown in the below picture(in the yellow circle)

https://i.ibb.co/CPcDc65/20241104-211556.jpg
https://i.imgur.com/2ppeTuF.jpeg

It seem that SV1021H PCB has three layers(top layer, ground layer, bottom layer) and I guess that this crushed track lead to short circuit(low resistance connection between HA13626 chip's pin5 and ground)..

That track leads to the voice coil.

_________________
A backup a day keeps DR away.

I measured the resistance between hitachi HA13626 chip's pin5 and ground pin of power connector in the working SV1021H PCB and It was measured 12k-13k ohm.
And I just have noticed that the resistance between hitachi HA13626 chip's pin1 and ground pin of power connector is measured only 10.1 ohm.
But On the contrary, the resistance between hitachi HA13626 chip's pin1 and ground pin of power connector in the working SV1021H pCB is measured 12k ohm.
I think that there is a need to replace hitachi HA13626 chip whether it have been really broken or not..

I also it very informative.