1 May
2010
1 May
'10
6:42 p.m.
I bought a case of (I think 1000) sony 3-1/2" floppies a few years ago,
along with a few packs of different colored ones. I also bought a case of 5
1/4 disks too. i'm sure they will still be on the market after production
for quite some time. as it is, there are still cassette tapes on retail
store shelves!
On Sat, May 1, 2010 at 1:50 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
The basic procedure is the same for all drives. You conenc the drive to
some device that will let you move the heads to a given cylinder (either
the machine the drive works with running a suisable program that talks to
the disk cotnroller, or a special floppy drive exerciser). You monitor
the output of the read amplifier (notmally using a 'scope). And you put
in a special 'catseye' alignment disk.
Then you step to the right cylinder and look at the read signal. It
should have 2 lobes Yiu loosen the head positioner moutings nad moce the
positioner until the 2 lobes have the smae amplitude. Clamp up the
positioner moutings and you're done
Now for the problems. The first is getting the alignment disk. They are
not commn (particularly the 3" one), they are not cheap, and they can't
be copied (for obvious reasons). The second is that uou normally need a
'scope. And you need to find where to connect this 'scope to the drive
electronics (the signals you need are the output of the index sensor as a
trigger and the differential outputs of the read amplidier). FInally
moving the positioner may be non-trivial. It's a delicate adjustment,
some manufacturers made speical tookls to make it easier -- but it's
possible to manange without them.
There was a produict called the 'microtest' that did away with the need
for a 'scope. It was a microcotnroller + ADC that linked ot a PC [1] serial
port. You connected the drive as drive B: o nthe PC (with adapters for 8"
drives, etc), and ran the suppleid software. You selected the drive type
from a menu, it showed you where to connec the test clips coming from the
ADC box, and then you put an alignment disk in the drive. You could see
how far off-alignment it was on the PC screen and adjust appropriately.
[[1] The minimum spec was 256K RAM and a serial port. And any display
adapter, even MDA.
The problem with the microtest is that (a) it only works for drives that
it knows about (which means not many modern ones..) and (b) the
instrument is not common. I was given one, and I use it for my older
drives. but for the modern drives I have to us a 'scope.
Actually the bigest problem is finding the testpoints. On old drives,
with simple chips (733s, 592s, etc) in the read chain it's pretty easy to
spot them. If you have the service manual (again more likely for older
drives) they will be shown. Most modern drives do have said testpoints,
if only as solder blobs on the PCB, but it can be a pian to work out
which poits to use. They are rarely marked.
> I
acutally wonder if they bother to align such drives=20
> at the factory, the price makes me wonder if they can, and tests on
a=20
couple of
such drives indicate they're not aligned properly...
Tony, is it easy to realign them? I would like to keep them in optimal condition (what I do now is clean them,
and keep them in a
plastic bag, to preserve them from getting dust, and put them into a
I would certianly use an anti-static bag!
box for storage on a clean, dry place. I would
like to realign them
properly before I put them in use again, if it's something easy to do
that I can do myself.
I don't worry about doing it if I have the right size alignment disk and
have some idea of the testpoints. For example when I was cleaning up an
HP9836CU I didn't worry about totally stripping the floppy drives
(losing the alignment)[2] because realigning them was not going to be a
problem. As I mentioned, when I bought my last floppy drive 15 years ago,
I also bought the service manual, wghich of course shows the testpoints.
[2] Althought I did scratch amarks on various parts of the drive, I also
seeked the heads to drive 0 using an exerciser and measured the clearance
between the head carriage and the end stop with a feeler gauge. And I put
things back ion the same positiones. This is not accurate enough to do
away with the need for a proper alignment but it meant that I could at
least find the right cylinder on the alignment disk :-)
I've come across some more modern drives that would not reliably read
disks formatted on my PC. I found what I think were the read amplifier
outputs and looked at hte catseye pattern with a 'scope. It was wildly
out (one lobe much larger than the other). Of course I might bave been
using the wrong TPs (say with a filter circuit in one side only), but
I moved the positioner to eqalise the lobes and the drive worked reliably
after that. I think it ws just badly aligned.
Also, any other advices on how to preserve, clean, store, etc. them I
would appreciate. :-)
Contrary to what it says in most manuals, I have never had any problems
cleanin the heads on any type of floppy drive uisng a cotton bud dipped
in propan-2-ol. You have to be careful not to distort the gimbal spring
for the upper head, but it's quite easy to avoid doing this.
Do you have any particular makes nad models of drives in mind? If we can
track doewn service manuals it would help...
-tony