Needed: 1 IBM 8" alignment disk. - test-drb@ccmp.vtda.org

29 Nov 1999

-----Original Message-----
From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Monday, November 29, 1999 9:15 PM
Subject: Re: Needed: 1 IBM 8" alignment disk.

...
 >
> Before I find the highest building to jump off of, I though I might ask here
...
 > first....
>
> I have a Sykes 7150 8" floppy drive (negibus PDP-8I) that I have invested
a
...
 > half and hour in and have solved *most* of
it's problems... It finally talks
...
 > to the PDP and I can select tracks, reset, read
status, etc... once in a
> while read a sector.
>
> I need a single sided 128 byte record alignment floppy.
>
> When I do a read now, the drive stays busy forever looking for the sector I
...
 > asked it for. (even if the head is on top of it).
Since it was made in 1974
...
   with TTL chips
it is only bright enough to sit there and *wait* for the
 correct data to come by. An alignment disk would make life a lot easier.

 Anyone have one available? Please e-mail.

 P.S. The sooner the better.. this thing is eating original IBM software
 diskettes from the early '70s 

Do you mean it's physically damaging those disks? Or it's erasing them?
Or what? Becase if it is, then the last thing you should do is feed it an
alignment disk (for obvious reasons).

When I do a write the logic happily kills *needed* data on the disk. It does
not erase them,.... it kind of writes what it wants to them.

...
 Normally, of course, you get the system working well
enough to
format/write/read a bulk-erased disk. It can do that however badly
aligned it is. And once it can do that it's safe to stick the alignment
disk in. But I assume that like many DEC and DEC-compatible systems, it
can't actually format a disk. 
That's right... this drive is pre '74.(an Orbis drive inside - serial #4) .
No formatting possible.. all TTL.. but  double buffered (really cool)...
about 170 ttl chips in the interface alone (8 boards)

This drive can be used on (according to the most recent manual):

PDP-11/20
PDP-8,8/s,8I
nova
hp 2100
varian 620 or 70 family

You just plug in one small interface board into the cage for each different
mini.
...

In that case, what I normally do is to put in a factory-formatted scratch
disk. Clip a 'scope to the outputs of the read amplifier and move the
head positioner slightly to peak the read amplitude. Sometimes it's
easier to find 2 points, one each side of the track, where the amplitude
has fallen off by the same amount and then to set it midway between them.

I did that (mentioned above).. I had the scope on the head... It did not
need alignment but looks like it might need a few TTLs...

...
 Once you've done that, the drive should be working
well enough to test it
fully. I'd not trust the alignment for real data like that (although the
last 2 drives I did this way were within spec when checked with a catseye
disk). But at least you'll know if it's safe to use the alignment disk.

I was hoping to use an alignment disk as this drive is filled with TTLs and
pots... The manual has many test points with pictures using the alignment
disk. I have no idea if the IBM system diskettes I have actually have a good
format on them (betting it)

...
 Sorry, BTW, I don't have an 8" alignment disk.
I wish I did...

-tony