In article ,
"Graham." writes:

I have dissected some recently. The Philips 11W ones were completely
dead, but the tubes themselves showed no discolouration at the ends,
so I took a look at the ballasts
The reservoir capacitors have gone high ESR, and are bulging
at the top.
http://myweb.tiscali.co.uk/infoweb/philips_cfl.jpg

I've had the capacitors die completely, but the ballast carries
on working, albeit with reduced light output and more difficulty
starting. My guess is that something else was the cause of death,
such as failure of the switching transistor. Normally, CFL's die
when the emission coating on the tube electrodes has all sputtered
off (same with most fluorescent tubes), but CFL ballasts can fail
if the lamp is operating in an unusually hot environment, such as
a pooly ventilated light fitting.

http://www.cucumber.demon.co.uk/lights/diy/

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]