On Mon, 14 Jun 2010 09:20:10 -0700, "William Sommerwerck"
wrote:

However, this begs the question of what caused the flames and
smoke? If the fuse was intact, it's unlikely. If it was an AC power
line fault of some sort (lightning hit, lost neutral, hi-v distribution
line falls on power line drop), it would have destroyed other pieces
of test equipment in the lab. Pardon my suspicious nature, but
methinks you should run it with the covers off and keep an eye
on this scope for a while.

Though Jeff is almost certainly correct, it's possible that the original
"blast" was caused by a screwed-up ground.

There would have been some evidence of the fire and smoke if it were a
bad ground. I've done it often enough. Fried scope probe leads were
common.

I haven't used my scope in a long time because I'm paranoid (probably
without reason) about connecting it to a DUT that is also connected to the
power line. (Go ahead, start throwing garbage at me for my
ignorance/stupidity.)

Ignorance is curable. Stupidity is not.

Get an isolation xformer and GRI power jack. Use it on whatever
you're testing. They have eliminated most of the pyrotechnics for me.

Most of my scopes are dual trace analog scopes which offer A-B
differential inputs. If you're not sure about the grounding, or
working on the AC mains side of the PS, this can be useful. Do *NOT*
connect the ground leads of the scope to the DUT. Instead, connect
the B channel input to the DUT common, and the A channel input to
whatever you're measuring. If you're not sure what you're dealing
with, use an isolated DVM to measure the AC and DC potentials before
applying the scope. If you have a large bank account, a battery
operated Fluke ScopeMeter is isolated from AC power.

Always remember that you have only one life to give to your chosen
profession.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558