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
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{ihnp4 [ucbvax | decvax!decwrl]!amd70 harpo hpda }!fortune!burton