[cctalk] Re: RD54 Maxtor XT-2190 w/one long meep

Unsticking stiction is different than dislodging a stuck actuator. Stiction is where the heads resting on the disk surface resist the torque of the spindle drive, causing the drive not to spin up. Generally it is caused by weak driver transistors in the spindle drive such that the spindle motor does not generate sufficient torque to overcome the static tension on the disk caused by the numerous heads sitting on it. This didn't happen on drives that retracted the heads either completely off of the disk surface, or had a ramp mechanism that raised the heads off the surface when the heads were retracted. The retraction would occur at power off when a large capacitor was discharged across the voicecoil with enough energy to pull the heads to the parking position. However, some drives actually had a dedicated landing zone on the disk surfaces where the heads could gently settle down (land) onto the disk surface as the platters spun down. It was this type of drive that tended to have issues with stiction. Other cases where stiction could become a problem is in situations where the power-off retract didn't work properly, leaving the heads in contact with the disk surface when they weren't supposed to be. In these situations, if the stiction was cleared by rapping the drive the right way, data damage could occur. In the case of stiction where there is a landing zone, since there's no data/servo information in the landing zone area, causing an abrupt acceleration in the correct axis could dislodge the heads, allowing the drive to spin up properly. So, rapping them with a hammer was a solution for these cases, though I typically used a small-sized dead-blow rubber mallet rather than a hammer, as it wouldn't induce as much resonance as rapping the HDA case with a metal-headed hammer. Also, I managed to use a variant of the "twist" method to clear stiction. I would hook a power connector to the drive, with a switch that switched the +12 and +5 power. I would hold the drive in one hand, and the switch in the other. I'd throw the switch to the ON position, and at the same time, give the drive a quick twist. The twist would accelerate the platters just enough to overcome the stiction such that the spindle drive could start up properly. I'd let it run long enough to warm up, then shut it off, and quickly hook it up to the archival system, and it'd properly spin up and I could get the data off. I also used the hammer method to release stiction. Another trick was for drives whose read/write amplifiers (which were typically situated within the sealed chamber, thus not replaceable except in a clean-room facility) had become flakey, and the drive would start getting lots of I/O errors. I would take the drive and put it inside a large ziplock bag, along with a bag of desiccant(this part is really important to suck up moisture in the air in the bag), and a small battery-powered digital thermometer. I'd put it in the freezer until the drive had reached roughly 42F, and then take it out, and immediately hook it up to an archival system and power it up while it was still cold. This would allow me to get the data off without I/O errors as long as I could get what I needed before the drive warmed up enough that the weakness in the amplifiers again became a problem. I found out about this trick somewhere on USENET many moons ago. It worked for me a number of times. I can't say that it'd work on anything more recent than /early/ 3.5" hard disk drives, though. Newer technology drives have such tight tolerances that the cooling might cause shrinkage that could cause head crashes, so take heed. -----Original Message----- From: Bill Gunshannon via cctalk [mailto:cctalk@classiccmp.org] Sent: Saturday, February 24, 2024 6:10 AM To: cctalk(a)classiccmp.org Cc: Bill Gunshannon <bill.gunshannon(a)hotmail.com> Subject: [cctalk] Re: RD54 Maxtor XT-2190 w/one long meep Back in the day when these disks were common I used to elicit a good laugh from my boss when I got out my little mallet and smacked the side of the drive. Stiction was the problem but a good hammer fixes anything. And, no, I never had it damage a disk. I guess it was all in the technique. :-) bill