8 Oct
2005
8 Oct
'05
6:51 p.m.
A disk drive performs several different functions. In
particular, it
rotates the disk, it detects the index hole and write protect notch, it
moves the heads between cylinders and detects the track0 position, and it
actually does the reading and writing.
This much I actually know :-)
Do you know which, if any, of these systems are
working? Can you get the
disk to spin? Do you get an index pulse? Can you get the head to move?
And so on.
All functions appear to work (Motor, Index, Step) - problem in all cases
is in the read/write circuitry. Drive goes through all the motions, it
just can't read/write.
A drive exerciser is handy for this, but by no means
essential.
Imagedisk's "Align/Test" function lets me excercise the drive with a fair
bit of manual control.
You can
often get away with just pulling pins on the interface connector low with
bits of wire connected to the 0V line. And look at the outputs with a
logic probe. Remembr there output drivers are open-collector, so you need
to add terminating/pullup resistors (traditionally 150 ohms to +5V) for
tssting.
Note that some drives with a big ASIC or microcontroller on them do some
kind of power-on initialisation. In particular, a few drives do odd
things if inputs are held active (low) at power-on. Other drives will
ignore all inputs if the power-on seek-to-track-0 fails.
If you have one of the latter units, you should be able to see
transitions on the stepper motor drive outputs just after power-on. And
you can check the track0 sensor by hand, of course.
All of this works.
I can't believe it would be that hard to trace out
a schematic. Even if
there's a big ASIC in the middle of the board (likely on half-height
drives), you can often figure out what it's doing from the surrounding
circuitry. You can at least check if things like senosr inputs do the
right things as you move a bit of card in and out of the sensor, etc.
It may come to this - At least I do have a couple of working drives
that I can compare signals with - but I asked in case a) someone has
the technical documentation or b) someone might say "oh yeah, thats
a common problem caused by xxx...", either of which could save me a
lot of time.
I think I agree with Allison however that these drives are crap, and
I'm not sure I want to spend a lot of time on them if suitable
substitutes can be found - in this case, the physical constraints make
this a but more challenging.
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.parse.com/~ddunfield/museum/index.html
9 Oct
9 Oct
5:34 a.m.
A disk drive performs several different functions.
In particular, it
rotates the disk, it detects the index hole and write protect notch, it
moves the heads between cylinders and detects the track0 position, and it
actually does the reading and writing.
This much I actually know :-) Do you know which, if any, of these systems are
working? Can you get the
disk to spin? Do you get an index pulse? Can you get the head to move?
And so on.
All functions appear to work (Motor, Index, Step) - problem in all cases
is in the read/write circuitry. Drive goes through all the motions, it
just can't read/write. It may come to this - At least I do have a couple of
working drives
that I can compare signals with - but I asked in case a) someone has
the technical documentation or b) someone might say "oh yeah, thats
a common problem caused by xxx...", either of which could save me a
lot of time.
I don't know how complicated these drives are, but I can't believe it
would tkae more than a day to figure out the read amplifier section, even
if it is hidden in the ASIC. Sometimes it's quicker to just sit down and
have a go :-)
I think I agree with Allison however that these drives are crap, and
I'm not sure I want to spend a lot of time on them if suitable
substitutes can be found - in this case, the physical constraints make
this a but more challenging.
Well, I like to keep my machines as close to original as possible.
-tony
2:21 p.m.
On Sunday 09 October 2005 08:34, you wrote:
One of the problems with this list is that it's impossible to know the
knowledge/skill level of the person asking the question.
Your original question did seem to suggest you thoguth of the floppy
drive as a single unit, whereas as we both know, it's a collection of
several systems. It certainly helps if we both know which of those
systems is the problem.
Ah, right (or is that Ah... Write :-)). Can you identify the read
amplifier chain (often using NE592 ICs), or is it hidden in an ASIC.
In the latter case, look for a pair of LC filter networks connected to
the ASIC. The read chain almost always consists of differential
amplifiers right up to the final comparator stage, so you expect filters
to come in pairs, etc. If you can find a pair of test point pins
associated with those, then they're almost certainly the outputs you'd
use for head alignemt. Hook a 'scope with differential inputs to those,
try reading a normal disk (never put an alignment disk into a dodgy
drive!). Do the signals look at all sane?
That fired a few brain cells that haven't been active for a long while...
Oh yeah..that's a common problem caused by the small inductors
in the read amplifier going open. too much stress on the leads.
Add a couple of years and bingo no read.
joe lang
A disk drive performs several different functions. In
particular, it
rotates the disk, it detects the index hole and write protect notch, it
moves the heads between cylinders and detects the track0 position, and
it actually does the reading and writing.
This much I actually know :-) Do you
know which, if any, of these systems are working? Can you get the
disk to spin? Do you get an index pulse? Can you get the head to move?
And so on.
All functions appear to work (Motor, Index, Step) - problem in all cases
is in the read/write circuitry. Drive goes through all the motions, it
just can't read/write. It may come to this - At least I do have a couple
of working drives
that I can compare signals with - but I asked in case a) someone has
the technical documentation or b) someone might say "oh yeah, thats
a common problem caused by xxx...", either of which could save me a
lot of time.
I don't know how complicated these drives are, but I can't believe it
would tkae more than a day to figure out the read amplifier section, even
if it is hidden in the ASIC. Sometimes it's quicker to just sit down and
have a go :-)
I think I agree with Allison however that these
drives are crap, and
I'm not sure I want to spend a lot of time on them if suitable
substitutes can be found - in this case, the physical constraints make
this a but more challenging.
Well, I like to keep my machines as close to original as possible.
-tony
10 Oct
10 Oct
8:55 a.m.
Oh yeah..that's a common problem caused by the
small inductors
in the read amplifier going open. too much stress on the leads.
Add a couple of years and bingo no read.
I've never had _that_ problem, but doubtless I will sometime...
One thing I forgot to mention last night is that another very common read
circuit uses the MC3470 chip. If you have one of those in the drive, it's
certain to be the read chain.
-tony
7013
days inactive
7014
days old
3 comments
3 participants
participants (3)
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ard＠p850ug1.demon.co.uk -
dave04a＠dunfield.com -
jclang＠notms.net