Floppy drive alignment

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Fujiyama
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Floppy drive alignment

Postby Fujiyama » Wed Sep 27, 2017 12:41 am

I just recently got hold of a (barely, if any use at all) Sony MPF-920 floppy disk drive from a PC which I changed the drive ID of and had working perfectly in a Mega STe until I accidently got its read/write head knocked out of alignment (don't ask) :x
At first I couldn't read any floppies at all with it, but then I inserted a floppy, started formatting and slowly moved the head around until the "hickups" stopped and it started stepping from track to track. It now formats about 3/4 of a full DD disk (I haven't tried it with a HD disk yet) and wonder if there's a simple way to get it better aligned? Perhaps some Atari software for this very purpose?

I've heard about alignment disks, but they're hard to come by and to my knowledge they only run on PCs.
What I do have is another fully working Sony floppy drive for the Mega STe (could be used for writing some reference material which the mis-aligned drive could try to read?) and some tools which might come in handy (oscilloscope, digital multimeter). Is there anything I can do short of guessing where the head should be by trial and error? With the ability to move the head both left/right as well as forward/back there's bound to be a lot of combinations, and I assume the need for accuracy is quite high as well.
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charles
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Re: Floppy drive alignment

Postby charles » Wed Sep 27, 2017 1:46 am

I have had a similar crippling effect with drives ,,,,,a good cleaning will help but do not unattach or resituate the drive head ,,, its impossible to reallign , but on a side note if you do misalign your heads ,,, u now have a machine which should still write and read disks only ones made inherent by the missalligned drive .
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Re: Floppy drive alignment

Postby czietz » Wed Sep 27, 2017 5:59 am

Of course an alignment disk will also work in the ST. There's even a menu item ("read alignment disk") for that in the diagnostic cartridge.

However, I fear it'll be hard to find such a disk. Also, without a schematic to your floppy drive, you won't know where to probe which signals coming from the drive heads; and without that you can't perform an alignment. Finally, if a drive cannot even write/read the disks it formatted itself, there might be something else wrong, as Charles already wrote.

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Re: Floppy drive alignment

Postby Fujiyama » Wed Sep 27, 2017 6:51 am

Unfortunately cleaning wasn't the issue here, Charles. It worked perfectly to begin with but the drive head got some unwanted handling in the process of modifying it for Atari usage. For the record, I have tried to carefully clean the heads with a Q-tip and isopropyl alcohol but to no avail.

Aha! I think I understand a bit more about the alignment disk, Czietz: there's an alignment disk which has probably been made from a very precisely adjusted disk drive to begin with and doesn't contain any software, then there's separate (commonly for Windows PCs) software used to analyze the data on that floppy while you simultaneously mechanically adjust the drive for the correct result.
Does that sounds about right?
I haven't been able to find any such disk for sale yet, and if they do show up they'll probably be more expensive than a new floppy drive (which is also getting increasingly hard to find, at inflated prices). Any suggestions as to where (new/new old stock) Sony MPF-920 drives can be bought?

It's funny you should mention the diagnostic cartridge because I'm going to attempt to incorporate one of those in my Discovery cartridge using the two empty ROM sockets.
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Re: Floppy drive alignment

Postby charles » Wed Sep 27, 2017 7:26 am

all the alignment disk does is tell you which head is giving bad reads ,,it doesn't realign the heads for you....
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Re: Floppy drive alignment

Postby czietz » Wed Sep 27, 2017 7:31 am

A basic realignment disk works as follows: It has some analog signal (no bits, i.e. no data) recorded to track 39.5 and some other analog signal at track 40.5. You set your floppy drive to continuously read track 40 (that's what the diagnostic cartridge does), then you measure with a scope the analog signal coming from the head at the test points you find in the drive's schematic. You manually realign the head until both signals have the same voltage level. Thus you know that you have reached the middle between 39.5 and 40.5, i.e. track 40.

On more advanced alignment disks there are more test patterns.

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Re: Floppy drive alignment

Postby Fujiyama » Wed Sep 27, 2017 7:40 am

I see. Several challenges here: getting hold of an alignment disk, the floppy drive schematic (or understanding which silk screen abbreviation to use in order to pick up the test signal) and building a diagnostic cartridge (which I intend to do anyway).

If I can find a new Sony MPF-920 drive (without costing an arm and a leg) that's probably the best solution. I was expecting them to be easy/cheap to find, but not so.
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Re: Floppy drive alignment

Postby joska » Wed Sep 27, 2017 8:21 am

It does not have to be that specific make and model. Most (all?) PC drives can be made to work in the ST/E.
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Re: Floppy drive alignment

Postby catmando » Wed Sep 27, 2017 10:29 am

There is an alignment program written for the amiga that you may be able to use if you have one of those too.
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Re: Floppy drive alignment

Postby clh333 » Fri Sep 29, 2017 12:30 pm

I got my 5.25 disk from http://www.accurite.com. 3.5s available as well. You'll also need a dual-channel scope.

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Re: Floppy drive alignment

Postby Fujiyama » Sat Sep 30, 2017 5:39 pm

Thanks clh333. I would probably look into that if I was to repair multiple drives, but for a single drive it's too expensive and too much of a hassle. I also don't have a dual channel scope (just a single channel one). But useful info to know in case I do.

I've found someone locally who has an second-hand Sony MPF-920 froma PC so I'm going to give that a go and hope for the best.
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Re: Floppy drive alignment

Postby Lando_C » Mon Feb 19, 2018 11:19 pm

if you only knocked the top head off, you can actually readjust without equipment, just carefully set the heads down on eachother without a disk in between (cheat the loading mechanism), and adjust until the edges of the heads are aligned visually both in/out and side/side directions. The worst case is you ruin a drive tha doesn't work anyway, the best is you have a working drive again. Did this to atleast 3 drives through the years, very seldom have troubles with disks, even switching between machines. it is rare to knock the bottom head, but common to hit the top one on disk insertion.. you tend to become fast and sloppy with diskchanges after a while on ataris...
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Fujiyama
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Re: Floppy drive alignment

Postby Fujiyama » Mon Feb 19, 2018 11:26 pm

Thanks. I haven't thrown away the misaligned drive even though I did get hold of another one (also second hand).
These sort of things seem to be harder to come across each day.
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