"Adrian C" wrote in message
...
On 17/06/2010 01:14, Arfa Daily wrote:

Last week, we had a couple of claps of thunder locally, so I began to
think that this might be a 'storm damage' job. Either way, in view of
its age, it was not going to be a practical repair, so I informed the
store that it came to me from, and put it back together. It was at this
point that I noticed the PAT test label wrapped around its power lead,
and this indicated that the test had been carried out only a week or so
before it became faulty. At this point, I began wondering if the fact
that it had had the tests performed on it, probably by someone with an
automatic tester and little understanding of what it is doing, and where
it is appropriate to run which tests, had resulted in damage to the
microcontroller. I have seen other equipment on a number of occasions
over the years, with similar 'odd' failures, and sometimes power supply
failures, shortly after being PAT tested.

Yup, PAT testing killed it, or correctly the incorrect procedure

This would have been Class II double insulated, so a tester would have a
choice of either a 'hard test' or 'soft test' to check the insulation
resistance, as part of the test.

The 'hard test' is a measurement of resistance (over 2Mohm ClassII) found
using a test voltage of 500V DC applied between 1) L&N connected AND 2)
any exposed possibly conductive surfaces (wandering probe)

The 'soft test' is powering the thing up normally on supply, and using a
wandering probe to measure any leakage current fron exposed possibly
conductive surfaces.

A 'hard test' is the thing for non-electronic equipment, 'soft' for
everything else. However, the wizzy do-everything electronic testers make
selecting soft and hard tests as easy as clicking a button, and mistakes
can and do happen.

I trained (C&G 2377) in doing this as a possible part/full time job, but
the risks of blowing up perfectly OK equipment, plus the meagre earnings
doing hundreds of items in an office, made me abandon the idea quite
quickly.

--
Adrian C

OK Adrian. That's just the sort of detailed and informed input that I was
looking for, and backs my feelings on the matter. I think I might mention
this to the shop who took this item in, when I return it tomorrow.

Arfa