Prev: Horizontal sync problem with Sony E500 monitor
Next: GE Cordless Phone Speaker Problem
From: Jeff Liebermann on 13 Jun 2010 20:33
On Sun, 13 Jun 2010 14:16:36 -0700 (PDT), powerampfreak
<powerampfreak(a)hotmail.com> 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 jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Phil Allison on 13 Jun 2010 21:25

"powerampfreak"
>
>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.


** For a glass fuse to shatter and blow like that, there has to be an arc
from end to end - which would explain the flame out the back. For there to
be an arc inside the fuse, the AC current has to be very high ( say 50
amps ) which means there was a virtual dead short on the other side of the
fuse.

That short may have blown open during the event, typically a copper track
vaporises or a semi blows open.

It may also be that a EMI suppression cap across the AC supply ( or supply
to chassis) shorted and then blew open.

Keep looking and checking things and you will spot something - like a pair
of wires poking out the PCB that connect to nothing.


..... Phil






From: powerampfreak on 14 Jun 2010 01:06
On 14 Juni, 03:25, "Phil Allison" <phi...(a)tpg.com.au> wrote:
> "powerampfreak"
>
>
>
> >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.
>
> ** For a glass fuse to shatter and blow like that, there has to be an arc
> from end to end - which would explain the flame out the back. For there to
> be an arc inside the fuse, the AC current has to be very high (  say 50
> amps )  which means there was a virtual dead short on the other side of the
> fuse.
>
> That short may have blown open during the event, typically a copper track
> vaporises or a semi blows open.
>
> It may also be that a EMI suppression cap across the AC supply ( or supply
> to chassis)  shorted and then blew open.
>
> Keep looking and checking things and you will spot something  -  like a pair
> of wires poking out the PCB that connect to nothing.
>
> ....  Phil

Great advice everyone! I'll continue investigating the powersupply
deeply!
I will let you know when I found out!
From: Falk Willberg on 14 Jun 2010 03:52
powerampfreak schrieb:
> I was given an oscilloscope, a Fluke PM3082 from a retired industrial
> electronics engineer.

....

> 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.

Once the SPS of a notebook computer made the mains circuit breaker
(16Amps) interrupt, while I connected it to an outlet. Big bang, arcs
and stuff.

It turned out, that one, maybe two, diodes in the rectifier was open
afterwards. The SPS is still working on 220V, on 110 probably not.

HTH,
Falk
From: JW on 14 Jun 2010 06:08
On Sun, 13 Jun 2010 14:16:36 -0700 (PDT) powerampfreak
<powerampfreak(a)hotmail.com> wrote in Message id:
<9d66d54d-7f21-418f-ac7e-78c950fd2391(a)z8g2000yqz.googlegroups.com>:

>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

IF you are sure there's nothing wrong on the primary, check for shorted
diodes and caps on the secondary side of the switching transformer. You
mention that you checked the "switch". Do you mean the power transistor(s)
that drives the primary side of the switching transformer?

As Jeff said, isolate the power supply from the rest of the scope if
possible. You should be able to use a lower rated fuse at this point to
help minimize any damage if you don't have any way to current limit the AC
input.

http://www.jetecnet.com/ claims to have a service manual for $10.

Might also want to search for free manuals for PM3084, PM3092, or PM3094.
They may share the same power supply.
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4
Prev: Horizontal sync problem with Sony E500 monitor
Next: GE Cordless Phone Speaker Problem