[cctalk] Re: Dysan Alignment and Performance Testers

It's a mechanical system, they're *all* old at this point. Some of them just go out of alignment from wear, heavy use, whatever. I've personally had TM-100s that came with systems I got in the mid 90s slowly become less and less reliable with reading diskettes written on other systems, or even sometimes ones written on that drive but 10+ years ago. Turned out to be marginal alignment. I wouldn't be surprised if drives also become more sensitive to marginal alignments as everything in them ages -- something like lower head output levels, sloppier stepper positioning, etc. In particular, I've had drives where the azimuth alignment ends up out, and on drives with non-adjustable azimuth I do wonder if they were just not super well aligned from the factory and finally wore enough to be out. I have not done extensive failure analysis as I use those drives which have uncorrectable alignment issues as parts to fix other drives (I now have a couple TM-100s where the only original parts are the frame and wiring!) Then there are of course alignment issues caused by break-fix repairs, like replacing an index sensor, a head carriage guide rod (even if you're careful you can knock it out of alignment), stepper replacement/new bearings, or anything where the carriage actually gets fully removed. Yes. If you want an alignment that allows reliable interchange, you need to align with an AAD. I have had to realign several "good enough using ImageDisk's beep alignment" hobbyist jobs done with factory written diskettes. With the AAD, it's immediately obvious that the alignment was marginal. You could do a media interchange dance between all of your available drives, but you'd still be in the position of maybe being misaligned to everyone else in the world :P If you don't care about interchange, the only really critical alignment is index alignment on hard sectored drives. That needs to be within tolerances or else you'll get missed sectors around the index. Some drives also have adjustable index skew, which is a special consideration of index alignment (e.g. Pertec FD-400 and FD-500 series, with leadscrews that are unsupported on the hub end) Thanks, Jonathan