Atari ST floppy drives and their limitations

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tzok
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Atari ST floppy drives and their limitations

Postby tzok » Mon Mar 05, 2018 9:23 pm

I've recently bought an SONY MP-F11W-U0 floppy disk drive in an unknown condition for a good price (~12€). It looked almost brand new, but had difficulties in reading and writing disks, especially 11 sector/track. I have cleaned it, and replaced two electrolytic capacitors: on +5V rail (47uF/6.3V) and in motor board (10uF/50V). I've decided to replace them, not just add 10uF to each one like Exxos suggests. After removing them, I've tested them and they seemed to be fine, only the 47uF had high current leakage (which would probably cured itself when left under power for some time). The one on 5V rail I have replaced with a 47uF/25V, and the one on motor board with a MLCC 10uF/25V (I've tried to measure voltage across it, but found almost nothing there - just some HF hum with amplitude of ~100mV). Now the drive works (almost) perfect...

But the topic was not meant to be about the repair (IMHO cleaning would be enough). This drive is not able to access tracks 83 and 84, while my EPSON SMD-380 easily formats and access disks with 84 tracks. Is this normal for this drive?

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Re: Atari ST floppy drives and their limitations

Postby 1st1 » Mon Mar 05, 2018 10:49 pm

Guaranteed is only 80 tracks, so you can be already happy with 82 tracks.
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Re: Atari ST floppy drives and their limitations

Postby 1024MAK » Thu Mar 08, 2018 4:47 pm

Yes, all 80 track 3.5" drives are, err, designed for 80 tracks...

Some can manage 81, 82, 83 or if you are really lucky, 84. But all that is happening, is you are taking advantage of an engineering tolerance.

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tzok
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Re: Atari ST floppy drives and their limitations

Postby tzok » Thu Mar 08, 2018 7:48 pm

Yes, but have anyone tested floppy drives used in various Atari ST, for how many tracks they support? After all, I think that each Epson SMD-380 will do 84 tracks.

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Re: Atari ST floppy drives and their limitations

Postby tzok » Thu Apr 19, 2018 12:15 pm

So far I've checked the following:
EPSON SMD-380: 84 tracks,
CHINON FB-354AA: 84 tracks,
NEWTRONICS D357: 84 tracks,
SONY MP-F11W-U0: 82 tracks.

Is there any list of FDDs used in the ST computers?

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Re: Atari ST floppy drives and their limitations

Postby ijor » Fri Jul 20, 2018 1:47 pm

I don't think anybody made a spreadsheet of tracks per brand and model, if that's what you mean. It wouldn't be perfectly accurate because models aren't always 100% identical. It is perfectly possible that a particular unit might support a different number of tracks than a different unit with the exact same model.

I believe most Atari branded drives do support 82 tracks. Some, of course, more. Some original disks require 81 or 82 tracks, IIRC only a couple use 83 tracks.

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Re: Atari ST floppy drives and their limitations

Postby rcamp48 » Sun Oct 21, 2018 6:34 am

My modified Sony MFP 920 does 11 sectors 86 tracks 2 sides reliably, unfortunately, I only have one but I have 2 spare ALPS drives all modified and set up for use on the Atari ST, do I have to modify the jumper to ds0 for an external drive on the Atari ST, and if anyone has an empty case that they want to sell with the power supply and cable I will trade a couple of modified ALPS floppy drives for just that. Maybe I can get a few Sony MFP 920 drives from my computer dealer. He only charges $5.00 Can for them. Russ


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