Macintosh LC thinks there's a floppy in the floppy drive

[olePigeon]

So I finally got a motherboard replacement for my broken LC, but it has a weird problem. When I connect a floppy drive, it'll constantly try to access the drive. It'll then pop up a message that there's a floppy disk it can't read and ask if I want to initialize or eject.

I tried several different floppy drives and both floppy ports on the motherboard, but the result is the same.

Any ideas? This makes my floppy drive unusable.

 

[LCGuy]

Have you tried a different cable? Also, have you tried both the cable and drives on a different Mac?

If you have, I'd say there's an issue with the SWIM chip.

 

[Bunsen]

I've had issues like that when connecting the wrong type of floppy drive to an older machine. Try an older drive, closer to the LC era.

 

[olePigeon]

I've tried three floppy drives. 2 are from LCs, 1 from a IIci. They all do the same thing even with different cables.

I do have my broken motherboard. Is there a way I can identify which chip controls the floppy drive? I could try swapping the chip over from the other one.

 

[Dennis Nedry]

I've tried three floppy drives. 2 are from LCs, 1 from a IIci. They all do the same thing even with different cables.
I do have my broken motherboard. Is there a way I can identify which chip controls the floppy drive? I could try swapping the chip over from the other one.

Sorry to pull up an old topic.

The SWIM chip is not the likely culprit. This is going to be a surface-mounted PLCC type chip which requires specialized tools and experience to remove and reattach.

I would first replace the capacitors on your logic board with tantalums, including thoroughly cleaning and inspecting the logic board and see if that fixes it. If not, I would then check the voltages of the power supply. After that, I would test supply voltages of the floppy port and supply voltages of the SWIM chip.

If the problem STILL exists, I would then investigate further exactly what signal tells the SWIM chip that there's a floppy inserted and trace that around on the logic board. The very last thing I would attempt to do is swap the actual SWIM chip, because of the dangers involved of permanent damage to the SWIM(s) and to the logic board. But try some of this stuff and let us know any new clues that appear along the way.

 

[techknight]

do the LCs have the R/C filter network like the older SEs did?

 

[BeniD82]

Not sure if this is related, but when modding the Colour Classic to fit a PPC board in it, you have sever one of the wires on the floppy cable to prevent the new PPC board from reading the floppy drive continously - if that pin is left connected, the floppy drive will infinitely "eject" no matter whether there's actually a disk in it or not ... Again, I'm not sure if this is the same issue, but I figured it's worth a thought.

-- BeniD82