Matthew Smith wrote:

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.)


snip
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.

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?)

I have gutted a couple Philips lamps with an LBA202(?) SMT IC.
Little else of interesting components in such a lamp...
All the rest (far Eastern, as well as European made Osram and Sylvania)
using a couple transistors in a power oscillator circuit.
Of the several (must be more than twenty!) I have gutted the
electrolytic most often has failed. I changed it in one of the lamps,
which held more than six months afterwards. The lamps which show
darkening of the FL tubes are nothing to keep, they probably are at the
end of life.
I have seen exploded transistors, but only in a couple of the lamps.
They are small video output transistors in a 'long TO92' case in the
far-East imports.
I collect the ferrite toroids and the hi-voltage caps after measuring
them. Some are nice replacements in tube gear..
The caps are marked with values and are nearly always within tolerances.


Some questions:

1) Does anyone have any figures for commonest causes of failure? (In
other words, where do I look first?)

Electrolytic. It dries out from high ripple current/high temp in the lamp.

2) Are the thermal fuses essential? Not all units seem to have them -
at least that I can identify.

Some have only a glass-cased fuse in one of the socket wires, some have
fusible resistors. I have seldom seen temp fuses.


Stein