Squeal on Older Hard Drives

Tony Duell wrote: Is it, though? The spring is not to ground the whole drive, it's to ground the spindle/disks. Apparently, static buildyp on the disks can cause read errors (it induces small signals in the read heads), and the bearings may not be that good a conductor due to the lubricant forming an insulating film. Certainly just about all hard drives (including the demountable ones on my '11s) have grounding contacts. You would therefroe think they performed some useful purpose. -tony It was a lot more serious than mere read errors. The static charge on the surface of the disks could build up to thousands of volts in just seconds. And its main discharge path was through the heads - they were the closest to the charge. I changed many a head on the early 14 inch drives that had a clean little burn hole right through the flying surface. The static discharge springs had a metal button that fit on the end of the spindle shaft. It was metal to metal so there was always some wear. If the button wasn't replaced when it wore, the charge wasn't bled off and sooner or later, took out a head and usually the preamp. Maintenance schedules always included cleaning and inspecting the springs. Very quickly, other schemes can into use that alleviated the need for the discharge spring. The most practical was a ferrofludic seal on the top of the bearings. The design goal was a path of around 10K ohm to ground. That would bleed off the charge but not put a spike on the ground. Tony is right about bearings not being that good of a path. But ferrofludic seals were excellent and the resistance could be controlled. They came in about the time of the transition from 14 inch to 8 inch drives. So some 14 inch drives didn't need a static discharge spring, but most did. I only saw one 8 inch drive with a discharge spring. After that, the ferrofludic seal was standard. I would never ever bend a spring away from the spindle. Too many bad experiences. The noise was a necessary pain. You can ease it by moving the spring slightly, so a different part of the button is touching. All the designs I know have oblong holes on the spring, so you can tweak the adjustment. It's unfathomable to me why an OEM would tell its customers to bend the spring away from the spindle. Billy