Hard drives manufactured in recent years store more data per square inch of platter area than ever before. This increase in data density each device is more complex and sophisticated than their predecessors.
To function at these high levels, hard drives are individually calibrated in the factory after assembly. The unique calibration parameters are stored on the hard drive, on the platter, on the control board, or both.
This customization means that the old trick of swapping one control board with another seemingly identical control board in an attempt to read a dead drive no longer works due to the fact that the calibration parameters are specific to each individual hard drive. The video above has more explanation, and a demonstration of how a control board swap fails between two drives, even though they’re from the same manufacturer and of the same model.