Sorry, trying to spice it up a bit. ESR is a large threat to the continued enjoyment of our beloved Personal System/2s. Mechanically, our wee bairns are rocks. But the electrolytic capacitors are mortal and are vulnerable to drying out due to a number of reasons, the worst being high temperatures.

Alan Douglas 
   I was going to look up Al's page and suggest this too.  I repaired
three such drives, following this suggestion to check the electrolytics for ESR (effective series resistance).
   They go open-circuit with age, and not just the ones circled on Al's
page, but caps in the motor-drive board too.  I found, as I recall, a
total of five open caps in three floppy drives.

   I replaced mine with ceramic (0.22µF) chips or tantalum chips. The
easiest way I found was to cut through the cans with flush-cutting
dikes, then remove the rubber seal, then unsolder each pad
individually.

   ESR is best measured in-circuit with the Dick Smith kit  or can be
done with a 100kHz generator  and a DVM.  Some pertinent web pages:

Designer Bob Parker's web page: K-7204  ESR meter  US$40.00
Stephen Powell''s 99 cent ESR tester: Info and links
USA: Anatek Corp (NH) 
Canada: John's Jukes (Vancouver) 
England: Satcure (Sandbach, Cheshire) 

Capacitor Testing, Safe Discharging and Other Related Information 
   Version 2.36   © 1994-2001  Samuel M. Goldwasser