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400K floppy drives redux - floppy Frankenstein project

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I thought about putting this in peripherals, but it seemed better here since this type of floppy drive mechanism is exclusive to the 128 and 512K Mac. It is also found inside the guts of M1030 400K external floppy drives.


As posted earlier (see links in this post), I have an early 128K Mac that is now fully functioning apart from the fact that it came to me with a non-working floppy drive. After a good bit of puzzling, I discovered that it was an original Sony OA-D34V 400K floppy drive (originally shipped with a stepper motor bearing the round sticker which should work in the 128K Mac with the Version A ROMs) with a stepper motor bearing the square sticker (more commonly found on the later OA-D34V-22 drives, and known NOT to work with the Version A ROMs). Since the drive itself bears a Feb 1984 production date, which predates the introduction of the square sticker stepper motor in summer 1984, I hypothesized that someone replaced the stepper motor on the drive at some point.


Apple's textbook fix for this problem is to swap Version A ROMs for Version B ROMs, since Version B ROMs can read both types of drives. I have acquired a set of Version B ROMs, and the ROMs are socketed and easily swappable, so I could put in the Version B ROMs, keep the Version A ROMs stored with the machine for authenticity, and call it done. I don't intend to sell the machine anyway. But my OCD brain really wants the original type of drive in the original Version A 128K, and Science brain wants to take things apart.


Frankenstein project: I have now acquired off ebay a collection of 5 400K drives, all pulled from 128K or 512K machines, all sold as non-working/AS IS (it was not totally clear to me whether the machines or the floppy drives had been tested and rated as non-working; possibly both, and I have visually examined the drives but not tested any of them yet). I paid more than I probably should have for this science experiment but I am measuring its value in hours of bench repair entertainment.


The drives are a strange mix, as follows:


April 84 - labeled OA-D34V - square sticker (I was disappointed to see this, as I knew one of the drives was an original OA-D34V and hoped it would have the round sticker)

October 84 - labeled OA-D34V-22 - round sticker

October 84 - no label where the OA label should be (?) - round sticker

November 84 - labeled OA-D34V-22 - round sticker

October 85 - labeled OA-D34V-22 - square sticker [this is the only "normal" drive out of the bunch]


What I am wondering is this: can I remove the stepper motor from one drive and install it on another without highly specialized equipment, or will I end up with a non-aligned head mechanism that won't work on any Mac? It would be fun to rebuild my original floppy drive with a working round sticker motor.


Another alternative is to see if the drives with the round sticker will work in my Version A Mac in spite of their OA-D34V-22 label. If the stepper motor is the only source of incompatibility, and Apple knew they had fixed the problem by instructing techs to install Version B ROMs in all machines with floppy drive incompatibility problems, they may have gone on for some months using up the "incompatible" stepper motor type in the Version B 128K machines they were selling up through late 1984. Nobody would ever know the difference since both types of drive worked with the Version B ROM machines.


I would welcome advice on the wisdom of moving stepper motors around before I attempt radical surgery. Otherwise, I will report back here on my progress! 

Edited by tanaquil
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