Re: Seeking APTEST

[Linards Ticmanis <ticmanis@gmx.de>]

David Chiu wrote:
> Thanks for all that replied. I have two Disk II clones (Mitac) and three
> or four half-heigh drives that won't read any disks anymore. Spindle
> speed looks fine, heads are clean too. So I am kind of at loss as to
> what else I can do with them.

A common failure mode is a destroyed 74LS125 chip in the drive. This is
usually a result of unaligned plugging of the drive into the controller
card. Also gone may be the ULN2003, but that is less common.

Drives with a broken 74LS125 are often in a "write-only" mode where they
will write to the disk surface at all times and never read. This happens
even with write protected disks, so be careful! These drives "eat" disks
by leaving a "spiral path of death" on the disk surface whenever you try
to CATALOG them or do something similar! (The data is gone, but the
disks can be salvaged by re-formatting in a working drive.)

Luckily the 74LS125 is the most common of all the chips in the drive.
Replacements are very easy to get.

-- 
Linards Ticmanis