NSM wrote:
....

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

I've heard it's a large electro (often in the base of the lamp) which is
often the fault.

I can vouch for that being the case in one of the failures I've observed
- end actually blown out.

After the posting regarding the poor soldering, I've found some very
dodgy looking joints on one of the units; I'll re-flow them and see if
that works - before I continue testing the components one by one.

Cheers

M