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Suggested forum title: Acer/Acros 325SE floppy belt replacement — drive spins but will not read DOS boot disk

E

ElComputadore

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Apr 30, 2026
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Hello everyone,


I am looking for help diagnosing the 3.5″ floppy drive in an Acer/Acros 325SE laptop. The drive is a slim belt-driven unit, apparently a Mitsumi D359C or similar 26-pin laptop floppy drive.


The original problem was a loose/deteriorated rubber belt. When powering on the laptop, the floppy motor would spin, but the disk itself did not rotate properly. I disassembled the drive carefully, removed the old belt residue, cleaned the pulleys, and replaced the belt. I mostly followed repair videos for similar slim 3.5″ laptop floppy drives. I did not intentionally loosen the head carriage, stepper motor, or any alignment-related parts.


After reassembly, the drive now spins, but the laptop still cannot boot from a known DOS boot disk. The BIOS first checks the hard disk, which seems to fail, then accesses the floppy for a few seconds and shows:


Insert system diskette and press Enter to reboot
Click to expand...

I first tried a 720 KB DOS 5.0 boot disk, then realized the machine likely expects a 1.44 MB drive, so I created a new 1.44 MB DOS boot disk from an image. The disk is writable/readable in another drive, but the Acros still does not boot from it.


I also bought a second cheap Acros 325SE. Its floppy belt was still installed, so I could see the original belt routing before replacement. I replaced that belt as well, and the result is very similar. This makes me suspect that I may be repeating the same reassembly mistake rather than having two drives with identical electronic failures.


Things already checked/done:


  • CMOS battery replaced on one unit.
  • BIOS settings checked.
  • 1.44 MB boot disk created.
  • Heads cleaned carefully with isopropanol.
  • Belt residue removed from pulleys.
  • Disk cage appears tight and the disk seems to sit in the correct position.
  • Motor runs during boot attempt.
  • The laptop does attempt to access the floppy.

My questions:


  1. Can removing/reinstalling the disk cage on these slim Mitsumi-style drives disturb disk clamping or head loading enough to prevent reading, even without touching the head alignment?
  2. Are there known reassembly traps with the cage, head-load spring, disk-present switch, write-protect switch, or HD-density sensor?
  3. How critical is belt thickness/tension on these drives? Could a belt that appears to work still cause wrong spindle speed or slipping under load?
  4. What is the best way to verify correct spindle speed and head stepping on this kind of drive?
  5. Does anyone have experience with the Acer/Acros 325SE floppy drive or the Mitsumi D359C 26-pin laptop drive specifically?

I can provide photos or videos of the belt routing, cage mechanism, and boot attempt with sound if that helps. Any advice on what to check next would be appreciated.1000067129.jpg1000067127.jpg
 
I only have experience with the Citizen W1D drive, which looks a lot like yours, but it uses a thin & wide belt, instead of a square belt like yours. I couldn't find belts locally so I 3D printed a belt with TPE or PEBA or one of those elastic filaments. I had to print a few to get the tension right, but it worked. Still works a year later.

All I can think is that your belt is too thin. It might stretch/contract causing unstable disk speed?

But I've only worked on one such drive. Others with more experience might give better advice...

Can you get the laptop to boot? Can you run IMD to diagnose the drive?
 
Quick note, your picture helped me reassemble mine. I don't think it'll work but at least it'll be together. It's not a square belt, it's a very small flat belt. I used a 2mm 7 inch long flat belt. It's the same drive as used in the grid 1660, 1660c, 1680, tandy 3830sl, and all variants of it.
 
errolt said:
I only have experience with the Citizen W1D drive, which looks a lot like yours, but it uses a thin & wide belt, instead of a square belt like yours. I couldn't find belts locally so I 3D printed a belt with TPE or PEBA or one of those elastic filaments. I had to print a few to get the tension right, but it worked. Still works a year later.

All I can think is that your belt is too thin. It might stretch/contract causing unstable disk speed?

But I've only worked on one such drive. Others with more experience might give better advice...

Can you get the laptop to boot? Can you run IMD to diagnose the drive?
Click to expand...
Hello, I am sorry for starting this back up but I got two of these laptops that have the same issue. I was wondering could you send the 3d file? Thanks.
 
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