On 8/20/22 08:42, Zane Healy via cctalk wrote: > > I have to ask, which is tragic? Needing to lookup SA400, or the fact that > webpage (from the Smithsonian), indicates it’s a 3 1/4” drive. That wasn’t > typo on my part they say *three*.
I do have a couple of the 3 1/4" drives and media to match, but they don't look anything like an SA400. I have only two memories of the SA400--the first was when a friend who was a hard-bitten KIM-1 addict got himself a KIMSI and a single-drive Integrand case to hold it all. I don't recall the S100 controller he used, but it was based on the WD1771. An SA400 drive completed the picture. He couldn't get the darned thing to work and turned it over to me to troubleshoot. It turns out that the big Integrand power supply transformer was throwing enough AC magnetic field to render the SA400 nearly useless when the drive was inside the box. Outside of the case, everything worked as expected. Eventually, the solution was to fabricate some steel shielding around the drive. The second instance was when work moved to new digs. We had a brand-new SA400 that was offered to me, because, in the words of the lead disk engineer, it was garbage. It sat around for a year or two at home, and then I stuck it into a 5150 PC. In comparison with the Micropolis drives that we'd been using, he was right. Eventually, an inductor on the tach board opened up and, after repair, the drive was given away. That plastic disc-and-follower arrangement was a terrible idea and the guys at Shugart must have known that. The guys from Micropolis were rightly proud of their precision-ground leadscrew technology and pointing out that the sheet-metal construction was far more precise than the Zamac castings that others were using. It was also far more expensive. IIRC, our OEM price for a carton of the 1115 drives was about $600 (1978 dollars) each. On the other hand, we were getting 460KB (77x12x512) on a single-sided disk using GCR and the WD1781 FDC, all on a Multibus-sized card. That would have been impossible on an SA400. The Micropolis drives were so accurate in positioning that we made our own alignment disks using one mounted on a 1/2" aluminum plate, driving the leadscrew through a 100:1 precision reduction. These disks were for field use, so it was acceptable to record tracks at various offsets to get a good idea of how far from the radial ideal the customer's drives were. I'm a bit surprised with the call for finding alignment disks, that this hasn't been done in the hobbyist world. After all, what most folks rehabilitating drives are interested in is radial alignment. I doubt that many know how to adjust azimuth. --Chuck
