Update on SA-800 Problem

Jay Jaeger cube1 at charter.net
Fri Aug 21 20:46:11 CDT 2015

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

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.


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