On Sun, 13 Jun 2010 14:16:36 -0700 (PDT), powerampfreak
wrote:

I was given an oscilloscope, a Fluke PM3082 from a retired industrial
electronics engineer.

When looking for a manual, also look for the Philips PM3082 scope.
It's a nice 100Mhz 2 trace scope probably worth fixing.

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.

Ask the retired engineer if there was more smoke than flame. My
guess(tm) is the traditional Philips fried electrolytic capacitors.
Flames mean that something caught fire, which is usually a resistor.
I've seen an amazingly large flame come out of power resistor, leaving
just a small burn hole.

Really don't know why the
mains fuse went.

Well, if it's not the primary, it's probably something shorted in the
output section of the power supply. My guess (again) are the
electrolytics. Do you have an ESR (equivalent series resistance) test
meter?
http://www.anatekcorp.com/blueesr.htm

I just don't want to put a new fuse in and try again, not before I
investigate the cause.

Can you disconnect the output of the power supply section by
unplugging something or cutting a wire/jumper? Take the load off and
isolate the power supply. Extra credit if you can separate the low
voltage and high voltage (CRT) power supply sections.

You might also want to use an AC isolation xformer, in case it really
was an internal AC power line fault, to prevent a repeat performance.

Could an incorrect measurement setup cause the mains fuse to explode?

Sure. Measuring something with an AC power line ground fault will
cause plenty of current to flow through the probes, case, and possibly
the internal circuitry. However, that usually fries the scope probe
and/or vertical input circuitry which is mostly near the bottom or
front of the scope. The back is inhabited by the power supply
section.

Anyone familiar with these scopes or perhaps has a service manual for
it?

Not. I'm familiar with earlier Philips scopes (PM3214 etc), all of
which have electrolytic capacitor issues. Replacing all the power
supply caps and some of the PCB electrolytics, usually revive them.

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