On 01/04/2014 02:48 PM, John Robertson wrote: In looking for them, and needing to formulate queries for eBay, be aware that in the IBM XT/AT world, they were rarely, if ever, called "test/service disc". With the exception of HP and audio derived "Compact Disc", the IBM PC world spelled it "DISK". Instead of "test/service", in the PC world, try "alignment disk" and "diagnostic disk", although the latter will also being up tons of only partially related stuff, such as the "Diagnostics Disk" that IBM provided with most of their early machines (which did NOT include any drive alignment or SERIOUS disk testing) The "regular"/"analog" alignment disk required a dual trace scope of at least 20MHz. It is, of course not duplicatable with stock hardware. The "digital" alignment disk, such as the Dysan "Digital Fiagnostics Diskette" required no other tools (if you don't own screwdrivers, etc., then abandon all hope NOW). It ran a program on the computer that attempted to read sectors on the disk recorded out of alignment. For example, for radial alignment, it had track(s) recorded with a sector in alignment, one further out from the spindle, one further in towards the spindle, one even further out, one even further in, and so forth. If the computer successfully read equal numbers of (further anf further out) V (further and further in) sectors, then the radial alignment could be assumed to be OK. OTOH, if it could read more (sectors further out than correct) than it could of (sectors further in than correct), that would provide an indication of misalignment AND of which direction. It is, of course, no duplicatable with stock hardware, although we did have one very stubborn guy on this list years ago who was adament that the copies of it that he made with CopyII were "just as good as the original" (although, with all sectors that were written aligned by his drive, said copies could certainly NOT be used for aligning disks). YOu COULD, theoretically, by adding a micrometer head to the head positioner mechanism, modify a drive to be able to create your own. -- Grumpy Ol' Fred cisin at xenosoft.com

On 01/05/2014 03:49 PM, Mark J. Blair wrote: I suspect that a good approximation might simply consist of taking a drive and placing the disk clamping mechanism so it rotates a bit off-axis. I remember this happening in response to a customer complaint--he had picked up a batch of floppies where an extra hub reinforcing ring was placed on each floppy. The result was that, although the floppy was clamped somewhat off-center, it formatted fine and verified the copy of data placed on it. Remove the disk from the drive and put it back in and almost nothing worked. I nearly went bald with frustration, until I noticed the extra ring. Removed it and everything was fine. (This is what happens when you buy floor sweepings for media.) So if you intentionally wr0te a bunch of off-center tracks, then transfered the disk to a known-accurate drive, you could see what ID header was in exactly the correct center-of-track position. Cheap, but perhaps effective. --Chuck

On Mon, 6 Jan 2014, dwight wrote: A good HOBBYIST way to check it. A manufacturer would use a CASLIBRATED head positioner with greater accuracy and different head than that of a consumer drive. The Dysan Digital Diagnostic Diskette wrote multiple sectors of varying mis-position within a track. THAT requires changing the head offset from spec position multiple times DURING the writing of a track. BUT, a homemade dgital alignment diskette could be made by writing an entire track 0.1mm off position, another entire track at 0.05mm offset, etc. It would not be as good, but it could still work, by comparing which TRACKS were readable by the suspect drive. For example, if it could read the correct track, and the 0.01mm too far in track, the 0.01mm too far out track, the 0.02mm too far out track, and the 0.03mm too far out track, and no others, then we would know that it was currently 0.01mm too far out. (Just being able to read the correct track is absolutely NOT an adequate indicator that the alignment is correct.) Ideally, there should be multiple copies of each offset track. The test read should include trying to read the given track by stepping OUT to it to try to read, AND stepping IN to try to read, to allow for lash/hysterisis/slop in the positioning mechanism. Alternatively, if the hub clamp is offset from the spindle, then you COULD write multiple offsets within a track, such as sector 5 is in correct position, sectors 1 through 4 could be varyning amounts of too far in, and sectors 6 through 9 could be varying amounts of too far out. Determining which sectors are which could be done with post writing measurement (use a narrow head on a known good aligned drive to see which sectors are which), OR by positioning index before clamping (as would be the case with 3.5"). A quetion for Tony, Chuck, Allison, etc. : We need to deal with 48tpi (5.25 and 8"), 96tpi (5.25") 135tpi (3.5"), and a few bizarre ones, such as 100tpi, etc. Looking at the 48tpi example: 48 tpi is approximately 1/2mm track to track spacing. The actual width of the track is approximately 1/4 mm. What offsets from spec would be needed to be able to reasonably check for alignment? -- Grumpy Ol' Fred cisin at xenosoft.com

On 1/6/14 2:53 PM, Chuck Guzis wrote: Would be nice to get that to go along with the 5" info I have on bitsavers.

On 1/6/14 6:52 PM, Chuck Guzis wrote: Thanks! just finished uploading it That reminds me I need to take some pictures of a Dysan test box that I picked up at the flea market. It uses a normal drive, so it won't write off track but it has a lot more circuitry than would be required for just an ordinary read/write circuit.

On 01/07/2014 10:31 AM, Chuck Guzis wrote: Since I've got it right here, I'll attach a link. Exactly what is the "Dysan Single-board computer"? --Chuck I've linked 1 file to this email: * ddd.zip (11.0 KB) hosted on Box: https://www.box.com/shared/ecwreweeq2y31zov6n12

How do you calibrate that head positioner? What do you measure, etc? I would ahve thoughtusign a travelling mciroscope to locate the track position (developed with magnasee) would be a reasoanble way to do that. Incidentally, does anyone know of a source of 3" (not 3.5") alignment disks? -tony