Greetings

Over the last couple of months, I have had a spate of failures of
compact fluorescent lamps (electronic ballasts). (All of the lamps in
our house, barring the ones that aren't kept on for any time, are CFLs.)

Whilst a couple have been generic Far-Eastern ones, I've had a couple of
failures of Philips units as well. (Back in England, one of the first
Philips electronic CFLs was still running well after seven years.)

One failure was within a week of installing a replacement - that went
straight back to the shop for replacement. (I've taken to writing the
installation date on the base.) In another, the electrolytic capacitor
had failed (end blown out); I replaced it and it runs fine, although I
have yet to replace the thermal fuse.

Of the others, it's a bit of a mystery; I've performed the following tests:
* Check appropriate DC voltage exists after bridge rectifier.
* Check electrolytic capacitor out of circuit.
* Check switching transistors out of circuit.

I'm now painstakingly tracing the circuits of two of the Philips units
so that I can mark up some voltage readings against "healthy" units. I
was rather surprised to find that even the latest units are constructed
with through-hole, discrete components. (What, no integrated switcher?)

None of the fittings are enclosed that the units would be getting
particularly hot.

We are on a single-wire (19kV SWER - read "highly unreliable power
supply") HV system - I don't know if this might have any bearing on the
problem (spikes, etc).

Some questions:

1) Does anyone have any figures for commonest causes of failure? (In
other words, where do I look first?)
2) Are the thermal fuses essential? Not all units seem to have them -
at least that I can identify. Whilst I'm not one to go removing safety
devices willy-nilly, more recent units do seem to have slightly lower
component counts, fuses included in some. Should I fit thermal fuses to
ones that don't have them?
3) Are these devices sensitive to spikes/surges and, if so, should I put
MOVs in any that I repair?

I know that these only cost $5 AUD each, but there's a principle at
stake here...

Cheers

--
Matthew Smith
South Australia