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Fujitsu M2551A Floppy Drives


New Member
Jan 7, 2020
Hello to everyone. It's been a few years since I last worked on these drives and visited any of the forums regarding the TI. I used to visit the Yahoo TI forum and the AtariAge forum with questions about this project. To bring you back up to speed, I was initially working on the CorComp disk controller cards after a static spike (my fault for not having grounded myself on a low humidity cold winter day while standing on carpet) ran through the card. I rebuilt both cards (one is the original CorComp release and the other is the revision "A" release) and now both are working just fine. Funny thing about the original release card was after I finished rebuilding it, it still didn't work. This was the card I bought off another member who said it would lock-up about 10 seconds after it was turned on. I thought there was a problem with one of the components on the board but it turned out to be it was missing the heat sink on the power transistor which caused it to shut down when it reached the thermal limit. Didn't need to rebuild the card after all. All it needed was a 50 cent heat sink! Oh well!

Anyway, after re-inserting the card into the PEB and hooking up the drives, I still wasn't able to read any floppys. The drives would just "chatter". This was caused by the read/write heads moving back and forth rapidly. I tried both cards but the result was the same. I bought a used Fujitsu M2551A08 floppy drive off eBay just to check if the cards I rebuilt were done correctly and I was able to read and load programs off the disk. This also proved there was nothing wrong with anything going backwards towards the computer such as the PEB interface card, the floppy drive cables or the card that is in the black square piece of the "foot" the connects the PEB to the TI. So the problem had to be in the drives themselves. I have been rebuilding the logic board a little at a time, replacing a component and then re-assembling it and testing it, but still haven't found the problem. I have replaced all the ICs, several transistors and resistors and the caps check out good with my ohm meter. There are still some things to replace but it occurred to me that maybe there is something wrong with the read/write head. Is this possible? I thought the head is basically just a magnet and how could a spike hurt a magnet? The internet has been no help with this question. There is also a diode called an ultra fast switching diode on the board which makes me believe it has something to do with switching the head movement from one direction to the other but I haven't been able to find out much about it or anywhere to get a new one. It is marked "154 WK". An internet search turmed up the description I mentioned above and an interchange number of NTE 19 but the picture I found of the NTE 19 doesn't look like it.

So does anyone have some experience with this and have any ideas other than just buy another floppy drive? I'd really like to save mine since good 5 1/4 drives are getting really scarce and saving a couple rather than throwing them out would be better. And there was someone I was having a conversation with on the Yahoo forum who was trying to assemble all the literature and programs he could get to create a TI archive and I promised him I would send him anything I have when I was able to get my drives working again. I haven't forgotten him or my promise so if anyone here can help me with this floppy drive problem I'd appreciate it and so would he.

Thanks for any help or ideas.
Those Fujitsu M2551A drives are generally nice reliable drives. I'd agree it would be best to repair them if possible.

If it were me, I would connect it to an IBM PC clone (it is a standard 360k floppy drive, and used in many PC clones) and test it with tools such as ImageDisk. ImageDisk will let you manually test head stepping, read and detect mis-aligned heads, and generally report detailed errors when something goes wrong. The idea would be to narrow down the problem, such as failing to detect track zero, issues stepping forward or back, read failure, write failure, index pulse detection failure, and so on.

Typically, if a read/write head fails, the drive will look as if it works but contains a completely bad disk. Although from my experience with the Fujitsu M2551A drives, a head failure does not seem likely. On other drive brands where heads fail typically the second head will fail and then only single sided disks will work, so that is easy to detect with tools like ImageDisk.
Hey SomeGuy. Thanks for a really informative reply. Glad to hear that it is unlikely that the heads are bad. It would be pretty tough finding them if at all. As for your suggestion to attach them to a IBM clone, that sounds good and I thought of it myself but was unsure what the result would be since IBM and their clones have a couple wires twisted on the floppy cable. Does this present a problem? According to Triton's info on these drives when I bought them, they said they were specifically made for the TI. If not, it would be easy for me to do this since I have an eMachines circa 2001 that has the 3.5 floppy drive which uses the same 28 pin connector as the TI and the BIOS Setup allows for 360K, 720K, 1.44 and 2.8 floppy drive configurations. Should I just swap the TI floppy cable with the clone cable or just use it as it is? And lastly, is Image Disk a free software download? Thanks!
Hi there, my COPAL does not work, I can't find any manual for it. Perhaps someone here has some more infos about that drive.


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