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

On Sun, 13 Jun 2010 14:16:36 -0700, powerampfreak �ʇoɹ�:

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

Flames out the back from an incorrect measurement set up? That would have
to have been one hell of a mistake.

On 14 Juni, 00:04, Meat Plow wrote:
On Sun, 13 Jun 2010 14:16:36 -0700, powerampfreak �ʇoɹ�:



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

Flames out the back from an incorrect measurement set up? That would have
to have been one hell of a mistake.

I appreciate your wise input!
What I was thinking about, was if he in some way measured on mains
live net for some reason.
Like if he forgot to use the isolation transformer.

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.

On Sun, 13 Jun 2010 15:10:58 -0700, powerampfreak �ʇoɹ�:

On 14 Juni, 00:04, Meat Plow wrote:
On Sun, 13 Jun 2010 14:16:36 -0700, powerampfreak �ʇoɹ�:



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

Flames out the back from an incorrect measurement set up? That would
have to have been one hell of a mistake.

I appreciate your wise input!
What I was thinking about, was if he in some way measured on mains live
net for some reason.
Like if he forgot to use the isolation transformer.

One would assume that this would be an unlikely scenario but not that far
removed from reality. Anything is possible I suppose and your knowledge
and diligence will no doubt find an answer. I would try to stick with the
cold hard facts and not let speculation muddy the waters.

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

"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

On 14 Juni, 03:25, "Phil Allison" 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!

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

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

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.

On 14 Juni, 12:08, JW wrote:
On Sun, 13 Jun 2010 14:16:36 -0700 (PDT) powerampfreak
wrote in Message id:
:



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.


I've examined the primary side of the powersupply very carefully.
Absolutely NO signs of damage anywhere.
The Y caps measures correct 2nF (2pcs of 1nF) also X cap ok at 0.22uF.
A NTC inruch limiter measures 15ohm, correct according to the text on
it, primary switch transistor ok, mains rectifier diodes ok all of
them...
But the curiousity took control over me. I cleaned up after the blown
fuse. Put a new one (1.6AT) - connected it to mains - and it works!
All channels and functions seems to operate just fine.
There are really no sign of flames anywhere. One thing which I haven't
paid any attention yet, is the mains filter which is an integrated
block of some coil and filtercaps encapsulated.
I will change the Y and X caps to make sure they're ok.
I've never seen a shorted secondary side make the mains fuse explode.
Just primary shorts has the power to do this, in my opinion based on
hundreds of smps repairs.
Anyway, it appears that I've got another nice looking four channel
oscilloscope on my bench! :-)

powerampfreak wrote in message
...
On 14 Juni, 12:08, JW wrote:
On Sun, 13 Jun 2010 14:16:36 -0700 (PDT) powerampfreak
wrote in Message id:
:



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.


I've examined the primary side of the powersupply very carefully.
Absolutely NO signs of damage anywhere.
The Y caps measures correct 2nF (2pcs of 1nF) also X cap ok at 0.22uF.
A NTC inruch limiter measures 15ohm, correct according to the text on
it, primary switch transistor ok, mains rectifier diodes ok all of
them...
But the curiousity took control over me. I cleaned up after the blown
fuse. Put a new one (1.6AT) - connected it to mains - and it works!
All channels and functions seems to operate just fine.
There are really no sign of flames anywhere. One thing which I haven't
paid any attention yet, is the mains filter which is an integrated
block of some coil and filtercaps encapsulated.
I will change the Y and X caps to make sure they're ok.
I've never seen a shorted secondary side make the mains fuse explode.
Just primary shorts has the power to do this, in my opinion based on
hundreds of smps repairs.
Anyway, it appears that I've got another nice looking four channel
oscilloscope on my bench! :-)









What are the primary side HV caps like? I would replace or at least remove
and inspect underneath.

On Mon, 14 Jun 2010 04:23:13 -0700 (PDT) powerampfreak
wrote in Message id:
:

One thing which I haven't
paid any attention yet, is the mains filter which is an integrated
block of some coil and filtercaps encapsulated.

I've been doing repair work for over 25 years, but until a few months ago
I had never seen one of those fail. Was repairing a Lecroy 9374 scope that
would run for a few hours, then blow the line fuse. Turned out to be the
chassis mount input filter. You could actually feel it running quite warm.

Glad to hear you got your scope up and running. If you don't already have
a operators manual, you can download one from Fluke.

On Mon, 14 Jun 2010 04:23:13 -0700 (PDT), powerampfreak
wrote:

But the curiousity took control over me. I cleaned up after the blown
fuse. Put a new one (1.6AT) - connected it to mains - and it works!
All channels and functions seems to operate just fine.

Congrats. I would have used an isolation xformer and variac, but if
you have a supply of fuses, that works.

There are really no sign of flames anywhere. One thing which I haven't
paid any attention yet, is the mains filter which is an integrated
block of some coil and filtercaps encapsulated.

Probably made by Corcom.
http://www.corcom.com
They can be blown by a lightning hit, but not much else.

I will change the Y and X caps to make sure they're ok.

Are there any MOV disks around the AC power jack? If yes, look for a
tiny hole where the flames exited.

I've never seen a shorted secondary side make the mains fuse explode.
Just primary shorts has the power to do this, in my opinion based on
hundreds of smps repairs.

Now that you mention it, you're right. Secondary shorts usually just
cause the switcher to shut down. If there are big fat capacitors on
the output lines (not commonly found on PC switchers), they could
store enough energy to blow the primary. I've seen secondary shorts
blow the primary fuse in "brick" type switching power supplies, but
not resulting in the blackened smoking mess you described. That would
require a short on the primary side.

Anyway, it appears that I've got another nice looking four channel
oscilloscope on my bench! :-)

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.

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

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.

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.)

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

On 14 Juni, 18:20, "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.

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.)


Took out the mains filter. It's a "konfektronics HGN365-2-F1". It
measures 5mH through each line and about 100nF across. This seems ok,
of course it can have some intermitent problem. It's a special type
with 5x20 fuse holder and internal mains switch which the switch on
the front of the scope alters, through a metal wire. I consider
letting this to be unchanged for the moment. It's still a mystery what
caused the original blast.
I'll have the scope up for longtime testing and see if it will re-
blast. :-O

On 14 Juni, 19:08, powerampfreak wrote:
On 14 Juni, 18:20, "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.

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.)

Took out the mains filter. It's a "konfektronics HGN365-2-F1". It
measures 5mH through each line and about 100nF across. This seems ok,
of course it can have some intermitent problem. It's a special type
with 5x20 fuse holder and internal mains switch which the switch on
the front of the scope alters, through a metal wire. I consider
letting this to be unchanged for the moment. It's still a mystery what
caused the original blast.
I'll have the scope up for longtime testing and see if it will re-
blast. *:-O

The powersupply input has no MOV. I thought this from the begining
until I realized it was a inrush limiter NTC.
Actually, if looking very close to the NTC body, there are a small
small mark in the middle, but not a hole.
If this was the source of flame I would suspect more evidence.

On Mon, 14 Jun 2010 10:15:57 -0700 (PDT), powerampfreak
wrote:

The powersupply input has no MOV.

It's usually on the fuse holder or input filter. The idea is that the
MOV should be the first device the power sees after the fuse, but
before any circuitry. For power supplies with AC connectors mounted
on the PCB, the MOV will of course be mounted on the PCB.

I thought this from the begining
until I realized it was a inrush limiter NTC.
Actually, if looking very close to the NTC body, there are a small
small mark in the middle, but not a hole.
If this was the source of flame I would suspect more evidence.

It's probably not the NTC thermistor. It looks very much like an MOV,
but goes between the input bridge and the input DC filter caps.
http://www.gesensing.com/downloads/datasheets/920_325a.pdf
If it were smoked, the resistance would be quite high and the scope
would not work. However, you might consider scraping the hole with
something sharp to see if it can be enlarged. If the outer coating on
the TNC themistor collapses into an internal cavity, then there's a
problem.

Got an IR thermometer? Wave it around the power supply and input
section to see if anything is hot and ready to blow.

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

On 14 Juni, 19:48, Jeff Liebermann wrote:
On Mon, 14 Jun 2010 10:15:57 -0700 (PDT), powerampfreak

wrote:
The powersupply input has no MOV.

It's usually on the fuse holder or input filter. *The idea is that the
MOV should be the first device the power sees after the fuse, but
before any circuitry. *For power supplies with AC connectors mounted
on the PCB, the MOV will of course be mounted on the PCB.

I thought this from the begining
until I realized it was a inrush limiter NTC.
Actually, if looking very close to the NTC body, there are a small
small mark in the middle, but not a hole.
If this was the source of flame I would suspect more evidence.

It's probably not the NTC thermistor. *It looks very much like an MOV,
but goes between the input bridge and the input DC filter caps.
http://www.gesensing.com/downloads/datasheets/920_325a.pdf
If it were smoked, the resistance would be quite high and the scope
would not work. *However, *you might consider scraping the hole with
something sharp to see if it can be enlarged. *If the outer coating on
the TNC themistor collapses into an internal cavity, then there's a
problem.

Got an IR thermometer? *Wave it around the power supply and input
section to see if anything is hot and ready to blow.

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


I actually got in touch with the industrial engineer who operated the
scope when it failed.
He said the scope was NOT under any measurements when the flame came
out of the rear!
It was just standing switched on and suddenly bang and flame......
It sure looks more and more to be the mains filter, though measures
fine.