Re: Troubleshoot a Disk ][ with no known-good anything?

[Linards Ticmanis <ticmanis@gmx.de>]

On 11/01/2010 09:06 AM, savant42 wrote:

> Is it possible to boot strap a floppy disk config utility straight
> into RAM, and then check that for timing issues?

All my drives have 50Hz and 60Hz stroboscope patterns on the bottom of
the mechanism. If yours has one of these too, all you need is a dark
room, an AC driven fluorescent lamp, and a decent provider of mains
power that keeps its frequency reasonably stable. With this, you should
be able to tune the motor speed close enough to 300 rpm to allow the
drive to operate at least on its own disks without problems, if that's
the issue.

For this, you can PRINT PEEK(-16246),PEEK(-16247) to turn on the drive
motor with no DOS loaded. Use PRINT PEEK(-16246) to turn it off. This
assumes you have your Disk II card in slot 6 as usual. You'll have to
insert a floppy and close the door obviously, to get the motor loaded.
Speed can be adjusted with the little screw on the right edge of the
smaller, vertical PCB inside the drive. Turn the screw very slowly, and
(just to be sure) mark where you started!

Also, there's one chip on the Disk II analog card (the larger,
horizontal PCB inside the drive) that fails often, it's luckily also the
one that's easiest to get (and it's socketed), a 74LS125 chip IIRC,
anyways it's the only 74 series chip on the board. This one tends to be
fried when people plug the drive into the card incorrectly, sending +12V
where it doesn't belong. The usual result of that chip's failure is the
Evil Disk Eating Drive From Hell(TM), which will erase any disk it tries
to read, even if write protected. So I recommend keeping any and all
disks with important date on it away from the drive until it's fixed.

-- 
Linards Ticmanis