Arfa Daily wrote in message
news:zNdSn.54051$Hs4.1013@hurricane...
Following on from my post of a couple of days ago, looking for a schematic
set for a JVC with a dead radio section, not having found one, I had a
little search through my extensive stock of JVC manuals, and came up with
one for a similar(ish) model of the same vintage, which used the same
radio
tuner sub-board.

Using this, I was able to determine that all rails were established and
correct, that the PLL chip was idling and unlocked, that the FM subsystem
IC
was idling, and that the VFD for the radio section had the correct
supplies
and drives, but was being 'muted' by the drive IC, which is also the
system
control processor. No I2C data was being sent to the PLL IC, hence the
reason that it never ramped the tune voltage to the RF module. The I2C bus
was however, correctly active for other control functions, such as
handling
the CD section. About the only conclusion that I could come to, was that
either the microcontroller was in some subtle way faulty or, more likely I
felt, its software was screwed.

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.

I've never been a great believer in the appropriateness of applying these
tests to double insulated and transformer based equipment, particularly
given that large DC spikes are applied, which with some testers are
actually
twice the nominal line voltage. Given that in much microcontroller based
electronic equipment, digital grounds are not directly bonded to other
system grounds, it seems to me that having big voltage spikes flashing
around between the primary side of the power supply, and cabinet
metalwork,
which is not grounded to any line power earth, but may well be AC common
to
internal DC grounds via low puff ( and sometimes not-so-low ) caps and
high
value resistors, is asking for trouble of the same nature as you might
expect from static damage, or pulse damage from nearby lightning strikes.

I would be interested in knowing if I'm on my own on this one, or if
anybody
else involved professionally in service work - or indeed anyone who
carries
out PAT testing - has any similar experience, or opinions on this.

Arfa


Now if it was actually a flash test not a pat test then who needs lightning.