An oscilloscope can be used to check ESR by using a very simple test circuit. All you need is a square wave generator (a 555 timer will do!) and a few resistors. The details are at my web page at

[URL=http://octopus.freeyellow.com/99.html]http://octopus.freeyellow.com/99.html[/URL]

There are some links to other related pages at

[URL=http://octopus.freeyellow.com/esr.html]http://octopus.freeyellow.com/esr.html[/URL]



Usually the kind of capacitors that have ESR problems are used to reduce voltage ripple in power supply...