Well, the Altos ACS-8000-2 power supply is all back together and working again, in reasonable health. And, as I posted a few days back, I swapped out the bearings. Unfortunately, that does not seem to have helped.
Now that the problem child is the second drive, though, I was able to put a floppy in, format it, and test it without removing it. When I do that, everything is fine for multiple consecutive tests, which means that the drive electronics, head and so on are fine. The problem does indeed have to be mechanical. I do note that the problems do tend to occur more on the inner tracks, so it is possible that there is wear on the positioner lead screw, I suppose. Now that this drive is the second drive, its electronics are more accessible. So, tomorrow I plan to measure the "wobble" on various tracks during multiple insertions, using a floppy that was only ever written on the good drive (which has never had a problem with floppies inserted later after formatting). I can also try my Siemens FDD 100-8 which has been reliable forever. (Eventually I'll get back to that spare SA-801 that took out the power supply in the first place to see where the problem is. If it is in its electronics, then I might simply meld the two drives into one.) One other thing I have noticed is that sometimes after a read problem on the bad drive the FD 1791 floppy controller chip seems to get into a "snit" that even a reset does not cure - I have to cycle power to get it back. Now that I have a reliable drive as the first drive, it is clear that this is not a reinsertion / wobble issue. So, I will have to check the reset line going to that and the PIO chip that supports it to see if there is a problem on the board. I also have some spare FD 1791's I can try, that are of a slightly later revision, to see if the problem is related to that specific chip. JRJ
