Two days ago, a small package arrived on my doorstep after 15 day’s worth of travel. Straight from China, 5 pc. of the L7251 spindle/VCM driver (remember the bad harddrive?), sold by Shenzhen Drivestar, who have a very friendly and competent customer service. Thanks again! I figured replacing the chip was the best option, looking at the chances of success.
Well what do you know. After soldering in one of these, the little sucker spins again. It is not accessible, yet, but this is definately progress! Even the o’scope shows perfect waveforms at the motor terminals, but listening to the clicking and squeaking noises I’d say something is wrong with the heads.
After investigating a little further, I spotted the central problem: The drive has suffered a triple headcrash, meaning three of its trackheads have touched the disc surface prior to the fault and were literally ripped to shreds – but in the wrong direction! The head assembly was bent and got stuck near to the platter edges, *almost* in the standby rack. Something prevented it from getting there, as it should automatically move and lock there as soon as the disc loses power. My best guess is that the disc stack rotated against its normal rotation direction, which can happen if you carry the drive.
To explain: Normally, the heads would create their own air cushion using the movement of the platters and “float” over the surfaces during operation. While the platters are motionless, that cushion is not present and therefore there is friction between the surface and heads – and any motion of the platters is also directed at the heads. For that reason, the heads have to be parked before the disc slows down too far. Usually, some kind of mechanical tensioner handles that part. It also ensures that the head assembly never moves freely while the drive is stopped.
The resulting braking force during spinup probably caused the controller to fail, and after repairing that part, the disk spun and pushed the head out of the platter spindle.
To sum it up, it is very likely that the surface of the lower platters is severely damaged, and even if not – the only way to undo this is to mount a new head assembly. I will look into this a little further, but for the moment that’s just that until I get around to building myself a small “clean room box” for repairs on discs and displays.