I have a

Seagate Barracuda 7200.8
400 Gb SATA
Model: ST3400832AS
P/N:9Y7385-301
Firmware 3.03
Date Code: 06227
Site Code: AMK

I recently recovered my friends SATA drive 320gb, also a Seagate, but it had a software/partition problem, not specifically related to that hard drive.
This unit wouldn't recognize in his enclosure and had that CRC error in windows where it would write to a portion of the drive and just drop off.
I remember picking this drive up and flicking it slightly and hearing spinning inside.

I have recovered from overheating and clicking seagates before where my promise sata controller would only detected on the second time.

The current drive baffles me.

A flick of the wrist causes the same light spinning sound as the 320gb but does not power up. Everything is plugged in properly and nothing. Dead.
The pcb doesn't seem to have any visible damage.
It did have a Vantec IceberQ Hard Drive Cooler bolted to the bottom.
http://www.vantecusa.com/front/product/view_detail/104.

This drive's power was connected in series with another sata drive and it is not affected.

I would assume that the drive would still recognize if the motor was dead or something was wrong with the heads because I had a maxtor that would spin up and get detected, even with grinding and clicking but the drive itself could not be accessed.....such as tests, recovery attempts and formatting. Since this drive makes no noise at all, and it does emit a spinning noise when given transferring some physical motion to the drive.

So its either the pcb or motor...

I want to replace the PCB on the drive, so, is there anything I should know about this drive and the process of swapping the pcb....

It seems not the pcb as the drive spins during transfer request. So it's not the motor. (this is what I understood). If the drive contains only downloaded or unimportant stuff, assume the risk and do some experiments. Otherwise, if you want to safely recover the data, PM me. Or ask any other pro.