On Jun 13, 2:16*pm, powerampfreak wrote:
I was given an oscilloscope, a Fluke PM3082 from a retired industrial
electronics engineer.
He said that during a measurement, the oscilloscope's powersupply just
bang and a flame came out of the rear panel. After this, the scope was
left for several years...until I got it.
The mains fuse has really exploded. Shattered glass in the fuse
holder. A brief examination of the primary side of the smps reveals no
shorts. The smps is an ordinary flyback supply. Mains rectifier ok,
switch ok, snubber, line filters all ok. Really don't know why the
mains fuse went.
I just don't want to put a new fuse in and try again, not before I
investigate the cause.
Could an incorrect measurement setup cause the mains fuse to explode?
Anyone familiar with these scopes or perhaps has a service manual for
it?
Best regards
PAF

I might suggest that you install a fuse that fits [the correct current
rating if possible, but not essential] and then do a 'Hi-pot' test
between the two mains prongs and the chassis/earth prong. It is quite
possible that in his test set-up that the earth prong was isolated
from earth and the 'scope chassis was raised way too far above earth
and caused a preakdown of the insulation betwixt the mains wiring and
earth internal to the 'scope. I would look particularly at the 'Y'
caps of the line filter since thay may have 'healed' after the fault
but could certainly have caused an explosion of the mains fuse if
there was sufficient power applied to the chassis from the test set-
up. An example could be measuring 550V or 600V non-isolated 3 phase
power where you might get 1000V between the chassis and 240V mains
power.
If such a thing happened, replacing the 'Y' caps [and fuse] might be
all that's required.

Neil S.