VOGONS


First post, by rpocc

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Hi, recently I’ve salvaged a pretty rare IBM PS/2 system (Model 35 386SLC in Model 56 enclosure, 9535-060)

I had it completely cleaned, removed rust and it does start up, and even after pressing F1 it loads MS-DOS installed by it’s last owner, but the floppy drive isn’t working.

All it does is rattling, trying to spin-up and something prevents it from that. I know that sometimes leaked electrolytic capacitors may cause that but I already replaced two pcs that I’ve found and nothing really changed. (Maybe replacements are bad too? Vloss or ESR issue?)

What else should I try? I have tools, scopes, meters, background in electronics, etc but just don’t have experience in stepped motors. At the same time this drive is so-called “Star” drive which is very rare and considering that I’ve got the whole computer for like $20, I wouldn’t like to spend at least another $75 or more on a replacement and would prefer to fight more for it.

Here’s the video of drive’s behaviour on Youtube: https://youtu.be/HyKhvZR4Cq0?si=a5eiDvU5dmeWSdHa

And here's are photos of the drive: https://mega.nz/folder/Eb1n3SSJ#-xK9k1O5YuOi91NaIF84fQ

The drive is Mitsubishi MF356F-899MF
IBM FRU: 64F4148

I believe it has Media-sense pinout and doesn't use 12V rail.

Update: I've just finally noticed that there is an inductor in series with the 22 uF capacitor which has one of it's lead ripped off to non-recoverable state. How could I find out the right inductance value for a replacement?

Reply 1 of 2, by Deunan

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The only inductor that's critical (well other than heads) is the spindle rotor sensor. Any inductors on the power lines can be bypassed with a wire for testing. If it works well that "fix" can be just left as-is. If you want to put something in there then just look for something that can survive 500mA current and is of similar size. The actual inductance won't matter much - if you more-or-less match the size and current then laws of physics will get you close enough to whatever value was in there before.

Reply 2 of 2, by rpocc

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Deunan wrote on 2024-07-16, 13:23:

The only inductor that's critical (well other than heads) is the spindle rotor sensor. Any inductors on the power lines can be bypassed with a wire for testing. If it works well that "fix" can be just left as-is. If you want to put something in there then just look for something that can survive 500mA current and is of similar size. The actual inductance won't matter much - if you more-or-less match the size and current then laws of physics will get you close enough to whatever value was in there before.

OK, thanks. Just replaced the dead one with random 3mH inductor from another broken drive and voila: it works and even reads and formats 2.88M floppies!