Portable M5126 Floppy Drive Behaving Weirdly

[CC_333]

Hi,

I've got my Portable more or less working now (good backlight and hard drive), but I can't figure out what's wrong with the floppy interface.

Every time I insert a disk, it goes crazy. Basically, it will go through a constant eject-format cycle (and of course the format fails), complaining that it can't read the disk. Funny thing is, it doesn't seem to recognize 1.44MB disks, as the only formatting options are single-sided (400k) or double-sided (800k). It locks up the machine so I can't use it unless I leave the floppy disconnected.

Floppy Emu works fine on the external port, so something must be weird on the internal (I'll have to connect my Floppy Emu internally to see what happens). I've read of people having bourns filter problems which exhibit symptoms not unlike these. How can I tell if that's the case here?

Should it be proven defective, would a bourns filter from, say, a battery-damaged SE/30, suffice as a replacement?

Thanks!

c

 

[bibilit]

The Superdrive has 3 contacts IIRC on the front end, instead of two for the 800 k variant.

maybe one is stuck, not giving the opportunity to determine the 1.44 Mb size.

 

[bibilit]

More information.

The switch on the left checks that the disk is/or isn't write-protected.

The two switches on the right are there to detect that the carriage is in the bottom position (so obviously that a floppy disk has been inserted) the far right one for disk size.

The 1.44 Mb disk has an extra hole :

https://farwestab.wordpress.com/2015/04/09/vintage-macintosh-floppy-disks/

If you are using a 1.44 mb disk, the last switch will go through this hole, won't be activated and will be detected as a proper 1.44 Mb disk.

If the disk is a DS/DD disk, the missing hole will press the switch down, and the system will ask to format the drive in one side (400k) or two sides option (800k)

If the last switch is stuck in bottom position, any floppy will be detected as a DD/DS one.

 

[360alaska]

I would plug the floppy emu internally and see what happens, and then try another floppy drive and see... You may have some bad traces going to your swim?

 

[CC_333]

bibilit: I forgot to mention that I swapped in a known-good drive, and the problem persisted. Good information, though. Thanks!

360alaska: This is actually a replacement logic board (the other one died a very mysterious death) which was fully recapped and tested working. I'll try the Floppy Emu internally to see what happens, but I just thought of something: is it possible a bad cable could cause this? I'll try swapping that around as well.

c

 

[techknight]

You may be losing the SWIM IC. these are known problem in the portable. 

A shot in the dark could be trying a floppy emu. it is known the 12V regulators can go crap in the portable, and the disk drive would freak out. But so would the hard drive as well. 

 

[CC_333]

OK. I forgot to mention that the "eject" command doesn't actually activate the ejector motor. It just sits there, being confused.

If the SWIM were dying, wouldn't the external port be acting weird as well?

c

 

[techknight]

Every port would be. Both ports share the same IC, and both ports share the same voltage regulators. 

HOWEVER. there are 3 ports. and they get muxed through a couple gates and the MISC GLU. any issues there could be the result of what your seeing.