schuster@dasys1.UUCP (Michael Schuster) (09/15/88)
Anyone want to take a stab at this perplexing hardware problem?
HARDWARE:
-520ST with 1MB upgrade.
-A: drive - original double-sided SF314 (Epson mechanism).
-B: drive - TEAC FD55BV 40-track 5.25" (IB Drive)
-Compaq 386 clone with 720K/1.44M 3.5" drive
-Both Atari disk drives run at 300 rpm (+/- 0.5) and seem to be in good
alignment as evidenced by easy interchangeability of disks with other
Atari users, even with extended disk formats. The PC drive has no
trouble with inerchange of even 1.44 MB disks with other AT users.
SOFTWARE:
-pc-ditto configured for 3.5" A: drive and 5.25" B: drive; name your DOS.
-TOS, 4/22/87 version, with verified pokes applied to change drive B:
step rate to 6 ms (I've tried it with 12, too).
SYMPTOMS:
-5.25" B: drive works fine for minutes to an hour or so, depending on
degree of activity. Suddenly it refuses to read or write reliably;
DOS reports "drive not ready"; TOS reports "the data on drive B: may
be damaged". Has happened during disk copy operations, so I can verify
it's affected both inner and outer disk tracks on the first sign of
trouble.
-3.5" A: drive works _perfectly_ in Atari mode. However, if the Atari
writes to an PC-formatted disk past track 65 or so, a PC then has
trouble reading the disk past that point. The Atari has _no trouble_
reading all 80 tracks of a disk formatted on the PC, but once it
writes to that disk past track ~65, the PC can no longer read it.
WHAT I'VE TRIED:
-Swapped cables: Oh, come on. You have to ask?
-Clean the heads: Yes, and inspected them with a mirror to be sure.
-Tried the IB drive on someone else's Atari: Cannot reproduce the
5.25" problem, even after hours of testing.
-Tried the IB drive mechanism on my PC: Yep, it works 100%
-Tried the Epson 3.5" mechanism on my PC: Yep, that works too.
-Tried a different 3.5" drive on the Atari: Well, my original B:
drive is another SF314. Same problem, same starting track #.
-Looked for thermal problems: Nothing gets especially hot. Yet, the
time-related start of this 5.25" stuff sure makes me THINK something
is overheating.
WHAT I SUSPECT:
I know the Atari disk controller setup is a total kludge, what with
unbuffered select lines coming off a SOUND CHIP and all. It sure
sounds to me like it's a wee bit flaky but I have no way to test it.
I've also hear things about write precompensation on diskette drives
too, and wonder if the track 65 stuff might have something to do with
that. Any of you disk drive mavens care to lend a hand? Thanks!
--
l\ /l' _ Mike Schuster {sun!hoptoad,cmcl2!phri}!dasys1!schuster
l \/ lll/(_ Big Electric Cat schuster@dasys1.UUCP
l lll\(_ New York, NY USA DELPHI,GEnie:MSCHUSTER CIS:70346,1745