Toshiba 2.5″ 250GB SATA HDD Mechanicals (HDD2D90)

A few days ago, I thought I’ve learned enough electronics to get something out of examining circuit boards in consumer electronics. Striking out on this Toshiba 2.5″ hard drive control board immediately after coming up empty on a Western Digital 3.5″ hard drive control board makes me think I’ve overreached too far beyond my skills. No matter, I’m still skilled with a screwdriver and can handle taking apart mechanical components.

Removing a rather large sticker label unveiled just one hidden screw.

After removing those screws, the lid came off easily.

I was surprised to find two platters was packed in this drive less than a centimeter thick representative impressive miniaturization at work. One difference between a desktop drive and this laptop drive is the read-write heads are physically pulled off the platter in parked position. I was under the impression HDD read-write heads are far too fragile for transition a gap between mechanical pieces or rubbing against anything other than a cushion of air. Seeing this tells me they’re not as fragile as I had thought, but I don’t know what the actual engineering constraints involved.

On the opposite end of the pivot, beyond the voice coil actuator, is this mechanism whose purpose I don’t fully understand. The pivoting metal arm could slot into a sharp hook next to the voice coil, keeping the read-write head away from the platter. But how does it know when to engage or not? It works in conjunction with the white plastic part, but I couldn’t figure out how the whole mechanism works together. My best guess is that we have a clever mechanism that would lock the pivot safely in place until the voice coil actuated pivot performs effectively a “secret knock.” Taking advantage of inertia and momentum, the right sequence of motion would release the lock. To verify this hypothesis, I would need to reassemble the drive and see if I can power it up, but by the time I thought of doing so, I had already passed the point of no return.

Because with the mystery latch removed, it was easy to remove the read-write head assembly and once I did, I could not put it back into place.

Flipping it over, I see a hex nut holding the entire stack together.

Loosening and removing the nut allowed disassembly of the entire stack.

I was surprised to find both platters were held by a single screw. Platters for large desktop drives always had multiple fasteners to ensure their platters could not rotate out of place. With a single screw, we don’t have that mechanical guarantee. I guess it’s just friction preventing these platters from rotating relative to each other or the spindle.

I was pretty impressed at how thin and compact this laptop hard drive was, but hard drive engineers have done even better than this.

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