[net.micro] apple drives

Damouth.Wbst@XEROX.ARPA (05/23/84)

There are at least two different "apple drives".  The old original is a
standard Shugart 390 mechanism, with Apple data handling electronics.  I
believe that the current drives are sourced in the orient, but have no
details.

If you have a Shugart drive, you should be able to purchase a service
manual directly from Shugart, 475 Oakmead Parkway, Sunnyvale Ca 94086
(408)988-2800.  If they don't have a 390 manual, you could also use the
manual for a 400, since the mechanism is identical (the 400 has data
electronics and a few extra goodies like an index sensor and head
lifting solenoid).  

First, however, do a few checks:  

(1) format a blank disk, write something, and try to read it.  If you
cannot read it, your problem is NOT alignment (or at least that's not
the only problem). You should be able to read your own recently written
disks even with badly misaligned heads.  if the newly formatted disks
read ok and the old ones (or disks written by others) don't work, you
can suspect alignment.  You need a special disk and an oscilloscope to
do alignment the official way, so the manual by itself won't help you
much.  It shouldn't cost much to get a local service shop to align it
for you.

(2) Check that the head is clean.  You don't need a manual for this.
Remove the cover and large electronics board (be careful with the small
connector to the head cable - it's fragile).  Lift the hinged pressure
pad out of the way, and examine the head.  If it looks clean and shiny,
leave it alone.  If it has visible accumulations of crud, scrub it clean
with a Q-Tip and pure isopropyl alcohol.  Don't use "rubbing alcohol",
vodka, etc.  The head cleaning solution sold for cassette tape decks is
ok (Radio Shack, etc).  Also look at the felt pressure pad. Standard
advice is to replace it with a new one.  I just lightly scrape the pile
surface with a knife edge, which dislodges the accumulated oxide, and
I'm still using my original five-year-old pads.  The manual claims that
after replacing the pad, you should rotate it a few degrees at a time
while monitoring read signal strength with an oscilloscope, leaving it
in the position that maximizes the read output voltage.  Before I
noticed that instruction, I had removed and replaced my pads several
times without paying any attention to orientation.  Since I have never
noticed any read errors, I haven't bothered to check the signal strength
and make the ajustment.  Maybe I'm lucky, or more likely, the Apple read
electronics has a wide latitude and Shugart is being over-conservative.

(3) Check the disk speed.  Some utility disks (such as recent versions
of LockSmith) include a program to measure and display speed.
Alternatively, there is a built-in strobe disk on the motor (at least
there is on mine).  You simply look at it in flourescent light and
adjust until the pattern is stationary with a disk inserted and the head
on a center track (a "catalog" command should get the head on the center
track).  The adjustment screw is on the little motor control board at
the back of the drive.  It's a typical long skinny 10-turn pot, and is
the only ajustment on that board.  Speed can be fairly far off before
problems occur.

(4) Check the cable and connectors between controller and drive.  You
could have a broken wire - the exposed cable takes a beating whenever
you move things around.

(5) If all the above doesn't fix it, your problem is probably in the
Apple electronics, and The Shugart manual won't help.  First borrow a
good controller board, to isolate the problem to either the controller
or the drive (or just interchange drives, if you have two).  I have
never seen any detailed description of the Apple controller and drive
electronics.  There is a schematic in the back of the DOS 3.2 manual
(and probably the 3.3 manual, although I don't have one handy to check).
The book "Beneath Apple DOS" explains in a general way what is going on
in the digital stuff, but pays no attention to circuit details.  If you
want to work blind, first check the ROMS on the controller - they seem
to be more fragile than the other chips.  

burton@fortune.UUCP (05/30/84)

#R:sri-arpa:-114900:fortune:28000042:000:473
fortune!burton    May 29 13:04:00 1984

**
The current apple drives are made by Alps Electronics, and were designed
(copied from Shugart ??) at the behest of Apple.  Apple's legal actions
against bootleg systems coming in from the Far East are as blatant an
example of corporate hypocrisy as one can imagine.

  Philip Burton      101 Twin Dolphin Drive-MS 133
  Fortune Systems    Redwood City, CA  94065	     (415) 595-8444 x 526
			      - - -
{ihnp4 [ucbvax | decvax!decwrl]!amd70 harpo hpda }!fortune!burton