The drive is a WD2500BEVS-75UST0. My laptop froze with a Windows black screen, followed by the drive clicking loudly. I turned off the computer and let the drive rest. I turned the computer back on and the drive started clicking loudly then spun down. I turned off the computer again. When I turned it on again, the drive didn't spin up at all and the BIOS said no drive detected.

I have checked the voltages where they are marked on the PCB and they all matched the voltage printed at the respective spots. When I block the preamp contacts with paper, I hear the spindle motor spin up (buzz) twice and then stop. When the PCB is installed with all contacts, nothing happens at all, no motor spinning.

I bought another drive to test out and practice with. I have been connecting in Windows 7 using a BlacX SATA to USB box with a SATA cable running from the BlacX to the drive being tested.
Patient PCB on patient drive: no spin up
Donor PCB on donor drive: runs correctly
Patient PCB on donor drive: no spin up
Donor PCB on patient drive: no spin up

I tried a hot swap:
Initialize donor drive with its own PCB and I see the drive in Windows Explorer with a small text file I saved to the drive for testing.
Let Windows go to sleep mode and transfer donor PCB (still connected to SATA cable) to patient drive. Open Windows from sleep. The patient drive spins up and clicks (softly, not loud like before). In Windows Explorer, I still see drive e: with my sample text file (as saved on the donor drive) showing. Should Explorer be showing the donor drive's files or should I see drive e: refreshed with the patient drive's files?

Since the drive was clicking, I put Windows back in sleep mode and disconnected the drive.

The donor drive is a WD2500BEVS-22UST0. I have read that I need to match the WD2500BEVS-__UST0 for donor drives. Is it OK to have -75 vs -22? WD's documentation says those numbers are for "internal use only" and designate a vendor code only.

8 letter DCM is matching all but the 6th and 7th letters.
Both made in Thailand.
Patient and donor manufactured 6 weeks apart.
On the PCB, I have matching 2061- code except the last letter is different (AD vs AE).

Does this sound like a PCB or mechanical issue? I am afraid it is the preamp/head assembly.

I can't find any listings of what the 8 letter DCM letters correspond to for laptop drives, only listings of 9 letter DCMs. Does anyone have the codes?

If I want to try another PCB where the 2061- number/letters match exactly, do I need to also match the DCM and or the -75? I see drives with -60UST0 and -22UST0 in addition to the -75UST0.

I have spent many hours reading these forums and searching the internet to learn what I can about my WD2500BEVS. Any help is really appreciated.

The bad of the internet is that there is not always an happy end.
What's worst, the problem is elsewhere (internal anyway) . No multimeter, datasheet and internet wisdom can resurrect a dead head or a firmware problem ( I vote for the first).

Thanks for the responses.

When I tried the hot swap should Explorer be showing the donor drive's files or should I see drive e: refreshed with the patient drive's files?

What hardware/software is required to read the adaptive info from the Marvell MCU chip and transfer to another PCB? My PCB doesn't have a U12 chip.

Do I need to match the vendor numbers in the model number? Do I need another WD2500BEVS-75UST0? or can I use WD2500BEVS-60UST0 or WD2500BEVS-22UST0?

Which letters in the 8 letter DCM code need to match on a donor to replace the preamp/head assembly?

Since the drive spun during the hot swap, how do I know it isn't the PCB and I need to find a better donor PCB and/or have someone (professional) copy the adaptive data from the MCU?

just one question : you seems not to know how precisely your hdd work and , in the vain hope to do it yourself , you just confused yourself with TMI (i.e. the hotswap and shown files...) . So said, you probably need cleanroom work (let alone the fact that there may be other problems next ...) and a precise diagnose first with pro gear, there is no alternative to it.
With a really expensive tool like PC3000 it is possible to rule out the problem with total certainty (with use of a loader first and some features).