"Sammy" wrote in message
...
Correction to my last message. . . I should have said that
the faulty component (diac)
is marked Z2 07D431K. It is blue, with 2 leads. It measures
low resistance
in both directions.

So it's a MOV, not a diac, as Franc pointed out. It serves a passive role
until there's voltage spikes etc and then presents a very low impedance
across the mains and blows the fuse and usually itself.

You can leave it out really, there's no user safety issues I can think of,
though a bad mains spike could take out the triac without one fitted, then
you'd get an 'always on' lamp. It's not like it's a box of sensitive,
expensive electronics though so I wouldn't worry about it too much.

At the very least, leave it out, replace the fuse and test the light, it may
well work. Replace the MOV once you've cleared the fault, if indeed there is
one other than the MOV itself, if you really feel happier with one back in
circuit.

You're lucky you didn't put two back to back diodes or whatever in its
place, they would have exploded and possibly embedded their casing in your
flesh or eyes! What made you think it was a diac? Did you give the circuit
layout a look over before you came to that conclusion? Diacs are always in
line with the triac gate, never across the supply!

A friendly tip: Always be sure about components before naming them,
misunderstandings can be very dangerous when dealing with mains operated
equipment.

Morse