<> I knew about that too, Those disks is too far expensive for few fixes
<> run to pay off in due time. :)
<
<It's not that bad. You only need 4 disks total - one of each size. They're
<no more expensive than the other test gear you really should have.
<
<If somebody could find a UK source of 8" alignment disks then I'd buy one
<_now!_
Dec diagnostic disks that havent been rewritten are generally very close to
nominal alignment.
<I was planning on removing the pin altogether and letting the head
<carriage move freely over the leadscrew. Then fit a micrometer head and a
<spring to pull the head assy agains the end of the micrometer. I should be
<able to get about 1" of calibrated head movement.
While you can do this there is one problem. Alignment disks are recorded
with a narrower than normal trackwdith and also stagger tracks (recorded
with offset either side of true) for alignment use.
Another tool you need is a source of 125/250/500khz pulses that conform to
FM timing (single density) for writing patterns. This is something you can
build out a handful of counters and a 4mhz clock osc.
Over the years I've found that if the drive needs alignment it's wise to
look for other problems like spindle and motor bearings that are tired
or head to actuator wear that will make for sloppy operation. Head
alignment can signal other problems. I retired a SA800 for spindle
bearings because the thing would not reliably read (had a new in the box
spare). Generally I've found that it's best to put aside those drives in
favor of a better one stealing the logic from it as needed. The only time I
would fix it is when there is really no other choice. Unless doing a museum
style restore I've found some drives are better dumped (sa400s in general)
in favor of other better drives of the era.
Allison
Received on Tue Aug 19 1997 - 08:10:01 BST