Electronics: this really is a repairWhere a drive shows no sign of life at all, the board has generally gone — a TVS diode shorted, electronics finished, a bridge chip on a USB drive that no longer answers. Each of those is a repair in the plain sense of that word, and they make for the cheapest news anybody here gets to give.
Firmware: mendable with the right kitDamage one module in the service area, or corrupt the translator, and a mechanically perfect disk will announce itself as 0GB, or vanish off the bus entirely. Reaching structures at that level takes purpose-built hardware. Nothing you can download gets close.
Mechanics: a single sweep and no moreA seized spindle freed, a donor stack fitted, heads lifted off a surface they had settled onto: what each of those buys is exactly the working life one complete copy requires, and not an hour beyond it. Outliving the job it was woken for is not what the mechanism is for.
Swapping the board stopped working long agoMeasurement happens once, on the production line, and the resulting figures end up in a ROM soldered onto whichever board shipped with that mechanism. Put a board off another drive on and the heads hand back noise instead of data. Your own ROM has to make the journey, and that needs a soldering iron and a programmer.