adams@svcrus.dec.com (BOB 223-7016 PK01/D-6-2) (11/18/87)
In article <1448@bsu-cs.UUCP>, cfchiesa@bsu-cs.UUCP (Christopher F. Chiesa) writes: > > I've just gotten thoroughly disgusted with my Percom AT-88 SS/SD 5 1/4" floppy > drive. It's been screwing up my disks more and more over the past few months, > and I finally "caught it in the act" today. [ description of error ... ] > Error appears to occur primarily with high-end (600 and up) sectors, when it > occurs (I was able to write that file to begin with, but glitched when trying > to alter it later). NO problem at ANY time with low and mid-range (360's) > sectors. > > 1) I'm hoping this is just a case of a dirty head: hasn't been cleaned > or otherwise maintained since I bought the drive in mid-1983. Can > anyone offer opinions on the likelihood of this being the cause? I don't think so. From past experience with many types of disk drives (mostly large mainframe types) and tinkering with my 8-bit drives when they bite the big one. I have found that this type of error is usually indicative of the carriage-way being out of alignment. A simple head out of alignment symptom will give you problems on all or most of the tracks at one time with the key symptom being that the drive will format, write and read itself just fine, which makes sense since the heads are in the same place for writing as reading even if that is the wrong place,but a disk written on a properly aligned drive (as is the case with store bought programs) can not be read on the misaligned drive.Also try formatting and writing all sectors on the drive in question and then trying to read what it wrote on a known good drive.This may or may not work since a drives alignment is only as good as the alignment disk used. And these can vary by more that you could believe. This is easily corrected if you happen to have a scope and alignment disk and diagnostic cartridge(which I do:-)). But your case is a little more complicated. It appears that the heads are not tracking in a perfectly straight line. So at track 0 the heads are in line but as they move closer to the spindle they angle either to the write or left and eventually are out of alignment. I don't know if the drive mechanism you are using has an adjustment for the carriage-way or if you could get someone with the right equipment to do it. You need a calibrated micrometer and a way to attach it to the carriage-way and some way to adjust it. I think it would be cheaper to just get another drive or head assembly. But before you trash the drive completely you could try to adjust the head alignment slightly in one direction and then test it. If it still doesn't work or if it is worse then try the other direction. Since the alignment has a margin in it for compatibility (slop) with other drives moving the alignment slightly like this may be able to compensate for the carriage-way problem. I have aligned my sisters drive like this in the past before I aquired the proper equipment and it is still working today. I formatted a disk on a known good compatible drive and then ran a program that tested disk speed constantly while I moved the alignment screw until the disk would read. The procedure took some trial and error and I actually ended up moving the heads much farther than I thought I would have to. After the drive will pass the speed test then try and test all the sectors on the known good disk. If it works your all set if not try it again if you have the patience. This procedure took me about 45 minutes (and I do it for a living). The final test will be to format a disk on the adjusted drive and then test all the sectors on your known good drive. GOOD LUCK. I hope I wasn't to long winded on this one. Bob Adams I.H.F.S. Digital Equipment corp. 126 Parker St. Maynard, Ma. 01754 PK01/D-6-2