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.