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James Sweet

wrote:
I am attempting to troubleshoot an electronic ballast from an 18W floor
lamp. The ballast is the plug-in variety at the end of cord. So far,
I've wrested open the plastic case and removed the blown in-line axial
lead 2.5A / 125V fuse from the circuit board. I've replaced the fuse
only to have it blow immediately upon plugging in the lamp. I'm as
green as you can be at electronic repair but quite curious. I have a
multi-meter. Any suggestions on narrowing down which component may be
bad?

Well go figure if the fuse blew there's a problem, at least you replaced
it with one of the correct value.

Usually when these sort of ballasts fail the culprit is one or both of
the power transistors in the output section are shorted. You may also
find shorted diodes in the area that were taken out in the process and
possibly some cold solder joints that caused the failure. Does your
multimeter have a diode check function? That's quite useful for testing
diodes and transistors.