Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Sharp microwave arcs *through* front door

I've got a ~2 year old microwave that has shown no previous signs of
trouble and is to all appearances in good working order. During
normal operation (melting butter on low power) this morning we heard a
familiar 60Hz buzz, and then sure enough it shot an arc out through
the door to metal rack across a gap of some two inches. Following the
burn marks back, the arc seems to have originated (or at least exited)
beneath the chamber, where the inside of the door meets the body of
the oven and roughly halfway across from the hinges. First the big
question: whatever the failure was, shouldn't there have been a
better path to ground available? Do I have some kind of grounding
issue that I need to fix in before I repair this thing and start using
it again? As for the cause of the arc, since it was able to arc
across such a large gap I assume the failure involves the high voltage
components, not the transformer or anything else seeing AC line power,
so maybe the diode? The capacitor would fail short, so that can't be
it, right? The local repair shop swore this was impossible, and I
haven't been able to turn up any previous posts covering external
arcs, except one from back in 2000 out the top of the oven, so
hopefully this isn't redundant. Has anyone else encountered something
like this or have an idea as to what might be going on? Thanks.

-Chris
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Default Sharp microwave arcs *through* front door

Are the door seals clean? Does the door close firmly and evenly?


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On Dec 15, 6:09 pm, "William Sommerwerck"
wrote:
Are the door seals clean? Does the door close firmly and evenly?


The door seals were passable, but not immaculate. The door itself
seems to close perfectly normally. It is relatively new and lightly
used, and there aren't any glaring issues like that. We did do some
work on our house a while back and stirred up a lot of dust in the
process, so contamination is a possibility. Supposing something like
that was the cause of the arc, shouldn't it have still have followed
some other path?
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Chris wrote:

I've got a ~2 year old microwave that has shown no previous signs of
trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)


That isn't a suitable load for a microwave is it ? You need some water in
there.

No surprise it arced.

Graham

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Chris wrote:

"William Sommerwerck" wrote:

Are the door seals clean? Does the door close firmly and evenly?


The door seals were passable, but not immaculate. The door itself
seems to close perfectly normally. It is relatively new and lightly
used, and there aren't any glaring issues like that. We did do some
work on our house a while back and stirred up a lot of dust in the
process, so contamination is a possibility. Supposing something like
that was the cause of the arc, shouldn't it have still have followed
some other path?


The cause of the arc was the absense of anything in the oven that could
absorb the microwave energy effectively.

Graham




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Default Sharp microwave arcs *through* front door

That isn't a suitable load for a microwave is it ? You need some water in
there.

No surprise it arced.

Graham


I thought about that, but then I've done it a hundred times with no
problem, and the micro wave has a build in 'melt butter' function,
which seems to run it on low power for short bursts. That's what we
were using at the time, so I dont think the load was the issue. Again
though, even if that were the problem, shouldn't the arc have been
contained?

-Chris
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Default Sharp microwave arcs *through* front door

On Sat, 15 Dec 2007 14:53:45 -0800 (PST), Chris
wrote:

I've got a ~2 year old microwave that has shown no previous signs of
trouble and is to all appearances in good working order. During
normal operation (melting butter on low power) this morning we heard a
familiar 60Hz buzz, and then sure enough it shot an arc out through
the door to metal rack across a gap of some two inches. Following the
burn marks back, the arc seems to have originated (or at least exited)
beneath the chamber, where the inside of the door meets the body of
the oven and roughly halfway across from the hinges. First the big
question: whatever the failure was, shouldn't there have been a
better path to ground available?


Yes, and you may want to check the outlet's ground wire just in case.
But the sink may have been a lower impedance ground?

Do I have some kind of grounding
issue that I need to fix in before I repair this thing and start using
it again?


Myself, I'm not sure I'd *want* to try to fix it!

As for the cause of the arc, since it was able to arc
across such a large gap I assume the failure involves the high voltage
components, not the transformer or anything else seeing AC line power,
so maybe the diode? The capacitor would fail short, so that can't be
it, right? The local repair shop swore this was impossible, and I
haven't been able to turn up any previous posts covering external
arcs, except one from back in 2000 out the top of the oven, so
hopefully this isn't redundant. Has anyone else encountered something
like this or have an idea as to what might be going on? Thanks.


Yes, check the door gasket?


-Chris

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Default Sharp microwave arcs *through* front door


"Eeyore" wrote in message
...


Chris wrote:

I've got a ~2 year old microwave that has shown no previous signs of
trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)


That isn't a suitable load for a microwave is it ? You need some water in
there.

No surprise it arced.



Even an empty microwave should never arc to the outside, I've never, ever
seen that before, and I too have used microwaves to melt butter hundreds of
times over the decades.


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Default Sharp microwave arcs *through* front door

"Eeyore" wrote in message
...

Chris wrote:


I've got a ~2 year old microwave that has shown no previous signs
of trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)...


That isn't a suitable load for a microwave, is it? You need some water
in there. No surprise it arced.


I don't think that's correct. Butter contains water and fat, both of which
absorb microwaves. I've melted butter without problems.

Arcing usually occurs at a sharp metal edge. I once put a plastic jar of
Adams peanut butter in my microwave to soften it up, and got serious arcing
on the teensy bits of aluminum foil that had been left behind when I peeled
off the inner seal.


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"Chris" wrote in message
...
On Dec 15, 6:09 pm, "William Sommerwerck"
wrote:


Are the door seals clean? Does the door close firmly and evenly?


The door seals were passable, but not immaculate. The door itself
seems to close perfectly normally. It is relatively new and lightly
used, and there aren't any glaring issues like that. We did do some
work on our house a while back and stirred up a lot of dust in the
process, so contamination is a possibility. Supposing something like
that was the cause of the arc, shouldn't it have still have followed
some other path?


¿Quien sabe?

I would thoroughly clean everything, inside and out. Also check to see that
there are no bits of foil, or anything metallic, in the oven, on or around
the seals, etc.




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Default Sharp microwave arcs *through* front door

William Sommerwerck wrote:
"Eeyore" wrote in message
...

Chris wrote:


I've got a ~2 year old microwave that has shown no previous signs
of trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)...


That isn't a suitable load for a microwave, is it? You need some water
in there. No surprise it arced.


I don't think that's correct. Butter contains water and fat, both of which
absorb microwaves. I've melted butter without problems.

Arcing usually occurs at a sharp metal edge. I once put a plastic jar of
Adams peanut butter in my microwave to soften it up, and got serious arcing
on the teensy bits of aluminum foil that had been left behind when I peeled
off the inner seal.


I've had that happen recently. Same product (different brand)--some
surprisingly SERIOUS fireworks immediately as I hit the button. If the
lights had been off, it would have lit the entire kitchen from really
minuscule bits of foil.

I'm with the other poster, in that I'm not sure I'd ever trust that unit
again.

jak
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Default Sharp microwave arcs *through* front door



I would thoroughly clean everything, inside and out. Also check to see that
there are no bits of foil, or anything metallic, in the oven, on or around
the seals, etc.


Yeah, I'll double check. Also noticed a second burn mark closer to
the hinges, but same vertical position. Just to clarify my
description of the problem, I'm not talking about an arc like you'd
see from a little metal in the microwave. I'm talking about a beefy
pink arc about the diameter of a pencil.
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Default Sharp microwave arcs *through* front door



James Sweet wrote:

"Eeyore" wrote
Chris wrote:

I've got a ~2 year old microwave that has shown no previous signs of
trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)


That isn't a suitable load for a microwave is it ? You need some water in
there.

No surprise it arced.


Even an empty microwave should never arc to the outside,


I agree it shouldn't have arced to the *outside*.


I've never, ever seen that before, and I too have used microwaves to melt
butter hundreds of
times over the decades.


Ok. I have heard of other stories where people have done things with their
microwave ovens the makers don't recommend and been puzzled why it broke after
say the hundredth time though.

Graham


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William Sommerwerck wrote:

"Eeyore" wrote
Chris wrote:


I've got a ~2 year old microwave that has shown no previous signs
of trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)...


That isn't a suitable load for a microwave, is it? You need some water
in there. No surprise it arced.


I don't think that's correct. Butter contains water and fat, both of which
absorb microwaves. I've melted butter without problems.


Maybe the quantity wasn't enough ?

Graham

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Nah, it was a half a stick, well within the pre-programmed range, so
that's not it. In any case, some bit of foil of just the right size
or shape can lead to gradients high enough to get sparks, but this was
not like this. This was some large fraction of the entire current
output of the transformer, like the fireworks you see on youtube when
people have pulled the guts out of the microwave and using it just to
make an arc.


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"Eeyore" wrote in message
...

William Sommerwerck wrote:
"Eeyore" wrote
Chris wrote:


I've got a ~2 year old microwave that has shown no previous signs
of trouble and is to all appearances in good working order. During
normal operation (melting butter on low power)...


That isn't a suitable load for a microwave, is it? You need some water
in there. No surprise it arced.


I don't think that's correct. Butter contains water and fat, both of

which
absorb microwaves. I've melted butter without problems.


Maybe the quantity wasn't enough?


I'm not sure. The "received knowledge" on such things is that if there's
nothing in the oven to absorb the microwaves, the magnetron will eventually
overheat (from the reflected unabsorbed energy). The lower the power
setting, the less likely this is to happen.

But overheating isn't arcing. Arcing requires a sharp metallic edge for the
electric field to build to a point where the air breaks down.


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"Chris" wrote in message
...

Nah, it was half a stick, well within the pre-programmed range, so
that's not it. In any case, some bit of foil of just the right size
or shape can lead to gradients high enough to get sparks, but this
was not like this. This was some large fraction of the entire current
output of the transformer, like the fireworks you see on youtube when
people have pulled the guts out of the microwave and using it just to
make an arc.


If a thorough cleaning and inspection doesn't resolve the issue, I'd get a
new unit. The potential for damage or injury seems too great.


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Chris writes:

Nah, it was a half a stick, well within the pre-programmed range, so
that's not it. In any case, some bit of foil of just the right size
or shape can lead to gradients high enough to get sparks, but this was
not like this. This was some large fraction of the entire current
output of the transformer, like the fireworks you see on youtube when
people have pulled the guts out of the microwave and using it just to
make an arc.


This whole thing doesn't sound right. Regardless of whether the microwave
oven is attached to Earth ground, the return path for the high voltage
IS the chassis of the microwave oven. It would be almost impossible for
that to be disrupted as the magnetron and HV transformer are bonded to
the chassis. So, it's highly unlikely that the HV current (not the
microwave energy) would want to jump from the oven to an external ground.
Looking at the typical schematic, it's hard to come up with any sort of failure
mode where such a potential difference would appear between the chassis
and ground.

I'm not saying something very peculiar didn't happen. Just that an
explanation relating to the HV power doesn't make sense. I'd quicker go
with some combination of load (butter), dirt, and other factors affecting
the microwave distribution.

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Default Sharp microwave arcs *through* front door

Sam Goldwasser wrote:
Chris writes:

Nah, it was a half a stick, well within the pre-programmed range, so
that's not it. In any case, some bit of foil of just the right size
or shape can lead to gradients high enough to get sparks, but this was
not like this. This was some large fraction of the entire current
output of the transformer, like the fireworks you see on youtube when
people have pulled the guts out of the microwave and using it just to
make an arc.


This whole thing doesn't sound right. Regardless of whether the microwave
oven is attached to Earth ground, the return path for the high voltage
IS the chassis of the microwave oven. It would be almost impossible for
that to be disrupted as the magnetron and HV transformer are bonded to
the chassis. So, it's highly unlikely that the HV current (not the
microwave energy) would want to jump from the oven to an external ground.
Looking at the typical schematic, it's hard to come up with any sort of failure
mode where such a potential difference would appear between the chassis
and ground.

I'm not saying something very peculiar didn't happen. Just that an
explanation relating to the HV power doesn't make sense. I'd quicker go
with some combination of load (butter), dirt, and other factors affecting
the microwave distribution.


It could be possible that some part of the door, possibly one of the
hinges has lost it`s bonding to chassis earth and a potential is
building up there then striking to the nearest earthed metal. it`s
unlikely tho in my experience.

There was a model of Phillips oven that could build up a charge on the
thin aluminium cover over the lamp leading to quite spectacular arcing
around the rivet which held it in place and acted as a swivel. A poor
connection there was indicated by quite strong leakage of microwave
radiation through the plastic menu strip on top of the oven.

Ron(UK)
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On 15 Dec, 23:09, "William Sommerwerck"
wrote:
Are the door seals clean? Does the door close firmly and evenly?


Mains wont jump 2 inches !!!!!!



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Marra wrote:
On 15 Dec, 23:09, "William Sommerwerck"
wrote:
Are the door seals clean? Does the door close firmly and evenly?


Mains wont jump 2 inches !!!!!!


It`s not mains voltage and it`s not mains frequency, is it?

Ron(UK)
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Thanks for all the replies. Its beginning to sound like I was right
to feel baffled. Its certainly not mains voltage, but before the arc
there was a buzz that sounded like mains frequency. Since you cant
see a flicker even at 60Hz (I'm in the US), I don't know the frequency
of the arc itself.

Ron: I had wondered if it was possible that the door had lost contact
(grease in the hinges?) with the chassis and was therefore able to
charge up. It still seems like it would have been easier to jump back
to the chassis than across the gap, but then I have two burn marks, so
maybe it went out into the door and then back to the chassis a ways
down for a while before hand?

Sam: I completely agree with both you and Ron that this seems far-
fetched. It seemed so unlikely that I started think I'd just made up
having seen the arc, and I wouldn't believe it if I didn't have the
burn marks staring me in the face. I also completely agree with your
reasoning for ruling out the HV as the explanation. Even so, I still
have some problems with the load explanation that I need to answer
before I trust my kitchen again. First, and most important, by the
same argument you made ruling out HV problems as the source, shouldn't
any spark created inside the oven by whatever mechanism be contained
by the chassis unless something has gone horribly wrong? On the other
hand, proceeding from the assumption that its impossible for the
entire chassis from floating up high enough to do this, is it even
possible for a load problem to cause a really large arc? In ballpark
figures, the oven is rated at ~1000 watts, the magnetron is some ~50%
efficient, say, so there can't be more than a than a few hundred watts
of microwaves bouncing around, right? Even if you made a tuned
resonator (one of these graphite and aluminum foil gizmos, for
example), and had no other load, is it possible to recover that energy
efficiently enough to something like this? At any rate, to be clear,
nobody thinks that in the absence of other problems I have reason to
doubt my house ground?

Thanks again. I'll keep cooking with one hand in my pocket for now.

Chris
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"Chris" wrote in message
...
I've got a ~2 year old microwave that has shown no previous signs of
trouble and is to all appearances in good working order. During
normal operation (melting butter on low power) this morning we heard
a
familiar 60Hz buzz, and then sure enough it shot an arc out through
the door to metal rack across a gap of some two inches. Following
the
burn marks back, the arc seems to have originated (or at least
exited)
beneath the chamber, where the inside of the door meets the body of
the oven and roughly halfway across from the hinges. First the big
question: whatever the failure was, shouldn't there have been a
better path to ground available? Do I have some kind of grounding
issue that I need to fix in before I repair this thing and start
using
it again?
-Chris


The only grounding isuue that I can think of that would cause this
type of fault is that your house is built on the site of an old indian
burial ground. You need an exorcist immediately.


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Chris wrote:
Thanks for all the replies. Its beginning to sound like I was right
to feel baffled. Its certainly not mains voltage, but before the arc
there was a buzz that sounded like mains frequency. Since you cant
see a flicker even at 60Hz (I'm in the US), I don't know the frequency
of the arc itself.

Ron: I had wondered if it was possible that the door had lost contact
(grease in the hinges?) with the chassis and was therefore able to
charge up. It still seems like it would have been easier to jump back
to the chassis than across the gap, but then I have two burn marks, so
maybe it went out into the door and then back to the chassis a ways
down for a while before hand?

Sam: I completely agree with both you and Ron that this seems far-
fetched. It seemed so unlikely that I started think I'd just made up
having seen the arc, and I wouldn't believe it if I didn't have the
burn marks staring me in the face. I also completely agree with your
reasoning for ruling out the HV as the explanation. Even so, I still
have some problems with the load explanation that I need to answer
before I trust my kitchen again. First, and most important, by the
same argument you made ruling out HV problems as the source, shouldn't
any spark created inside the oven by whatever mechanism be contained
by the chassis unless something has gone horribly wrong? On the other
hand, proceeding from the assumption that its impossible for the
entire chassis from floating up high enough to do this, is it even
possible for a load problem to cause a really large arc? In ballpark
figures, the oven is rated at ~1000 watts, the magnetron is some ~50%
efficient, say, so there can't be more than a than a few hundred watts
of microwaves bouncing around, right? Even if you made a tuned
resonator (one of these graphite and aluminum foil gizmos, for
example), and had no other load, is it possible to recover that energy
efficiently enough to something like this? At any rate, to be clear,
nobody thinks that in the absence of other problems I have reason to
doubt my house ground?



Thanks again. I'll keep cooking with one hand in my pocket for now.



If I were you, I`d replace the oven!


Ron(UK)
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Chris writes:

Thanks for all the replies. Its beginning to sound like I was right
to feel baffled. Its certainly not mains voltage, but before the arc
there was a buzz that sounded like mains frequency. Since you cant
see a flicker even at 60Hz (I'm in the US), I don't know the frequency
of the arc itself.

Ron: I had wondered if it was possible that the door had lost contact
(grease in the hinges?) with the chassis and was therefore able to
charge up. It still seems like it would have been easier to jump back
to the chassis than across the gap, but then I have two burn marks, so
maybe it went out into the door and then back to the chassis a ways
down for a while before hand?

Sam: I completely agree with both you and Ron that this seems far-
fetched. It seemed so unlikely that I started think I'd just made up
having seen the arc, and I wouldn't believe it if I didn't have the
burn marks staring me in the face. I also completely agree with your
reasoning for ruling out the HV as the explanation. Even so, I still
have some problems with the load explanation that I need to answer
before I trust my kitchen again. First, and most important, by the
same argument you made ruling out HV problems as the source, shouldn't
any spark created inside the oven by whatever mechanism be contained
by the chassis unless something has gone horribly wrong? On the other
hand, proceeding from the assumption that its impossible for the
entire chassis from floating up high enough to do this, is it even
possible for a load problem to cause a really large arc? In ballpark
figures, the oven is rated at ~1000 watts, the magnetron is some ~50%
efficient, say, so there can't be more than a than a few hundred watts
of microwaves bouncing around, right? Even if you made a tuned
resonator (one of these graphite and aluminum foil gizmos, for
example), and had no other load, is it possible to recover that energy
efficiently enough to something like this? At any rate, to be clear,
nobody thinks that in the absence of other problems I have reason to
doubt my house ground?


Did the fireworks happen *instantly* when you pushed START? Instantly
means in a fraction of a second.

Any effect would have 60 Hz in it since the microwaves are generated in
pulses that have 100 percent ripple at 60 Hz.

Could there be a 2 inch arc from 1000 W of microwaves? Sure.

And a half stick of butter or whatever is probably not a very good
absorber so some sort of peculiar resonant cavity effect is quite
possible. And, if there was dirt, grime, and goop in the area
of the door where the arcing took place, even more possible.

Beyond that, I'd say you have to try some more experiments. :-)

To be sure, check your outlet ground with a multimeter or outlet tester.
But plenty of microwave ovens are used without proper grounds despite the
warnings.

I can't imagine any problem with the house ground that wouldn't result
in other issues.

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Ron(UK) wrote:
Chris wrote:


snip




Thanks again. I'll keep cooking with one hand in my pocket for now.



I can understand a purely academic curiosity as to the cause of
this--and I sympathize with the economics involved--but I think
(actually, I'm sure) if it were me, I'd follow the advice below.

If I were you, I`d replace the oven!

Failing that, I'd get professional--and by professional, I mean
engineering--help. Either involve the manufacturer, and/or a consumer
products testing agency. This just ain't s'posed to happen, doesn't
often--if ever before--happen; and most importantly, involves serious
safety issues.

You may trigger a product recall, save some lives or prevent some
injuries...and maybe even get a new oven in the process.

Failing all that, toss it and pick up one for $15-25 at a thrift store.
I've done that many times....

jak

Ron(UK)

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This unit is defective. The manufacturer should be contacted for a
replacement. Discontinue use at once. Fireworks inside are one thing.
The moment they reach outside, it is something entirely different!
Large amounts of microwave energy are leaking and could seriously burn
your eyes, nasal passages, lungs and internal organs before your skin.

Stop screwing around with this one.

The manufacturer SHOULD be willing to replace it for the sake of
liability alone.





On Dec 17, 8:32 am, Sam Goldwasser wrote:
Chris writes:
Thanks for all the replies. Its beginning to sound like I was right
to feel baffled. Its certainly not mains voltage, but before the arc
there was a buzz that sounded like mains frequency. Since you cant
see a flicker even at 60Hz (I'm in the US), I don't know the frequency
of the arc itself.


Ron: I had wondered if it was possible that the door had lost contact
(grease in the hinges?) with the chassis and was therefore able to
charge up. It still seems like it would have been easier to jump back
to the chassis than across the gap, but then I have two burn marks, so
maybe it went out into the door and then back to the chassis a ways
down for a while before hand?


Sam: I completely agree with both you and Ron that this seems far-
fetched. It seemed so unlikely that I started think I'd just made up
having seen the arc, and I wouldn't believe it if I didn't have the
burn marks staring me in the face. I also completely agree with your
reasoning for ruling out the HV as the explanation. Even so, I still
have some problems with the load explanation that I need to answer
before I trust my kitchen again. First, and most important, by the
same argument you made ruling out HV problems as the source, shouldn't
any spark created inside the oven by whatever mechanism be contained
by the chassis unless something has gone horribly wrong? On the other
hand, proceeding from the assumption that its impossible for the
entire chassis from floating up high enough to do this, is it even
possible for a load problem to cause a really large arc? In ballpark
figures, the oven is rated at ~1000 watts, the magnetron is some ~50%
efficient, say, so there can't be more than a than a few hundred watts
of microwaves bouncing around, right? Even if you made a tuned
resonator (one of these graphite and aluminum foil gizmos, for
example), and had no other load, is it possible to recover that energy
efficiently enough to something like this? At any rate, to be clear,
nobody thinks that in the absence of other problems I have reason to
doubt my house ground?


Did the fireworks happen *instantly* when you pushed START? Instantly
means in a fraction of a second.

Any effect would have 60 Hz in it since the microwaves are generated in
pulses that have 100 percent ripple at 60 Hz.

Could there be a 2 inch arc from 1000 W of microwaves? Sure.

And a half stick of butter or whatever is probably not a very good
absorber so some sort of peculiar resonant cavity effect is quite
possible. And, if there was dirt, grime, and goop in the area
of the door where the arcing took place, even more possible.

Beyond that, I'd say you have to try some more experiments. :-)

To be sure, check your outlet ground with a multimeter or outlet tester.
But plenty of microwave ovens are used without proper grounds despite the
warnings.

I can't imagine any problem with the house ground that wouldn't result
in other issues.

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
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Default Sharp microwave arcs *through* front door

This unit is defective. The manufacturer should be contacted for a
replacement. Discontinue use at once. Fireworks inside are one thing.
The moment they reach outside, it is something entirely different!
Large amounts of microwave energy are leaking and could seriously burn
your eyes, nasal passages, lungs and internal organs before your skin.

Stop screwing around with this one.

The manufacturer SHOULD be willing to replace it for the sake of
liability alone.





On Dec 17, 8:32 am, Sam Goldwasser wrote:
Chris writes:
Thanks for all the replies. Its beginning to sound like I was right
to feel baffled. Its certainly not mains voltage, but before the arc
there was a buzz that sounded like mains frequency. Since you cant
see a flicker even at 60Hz (I'm in the US), I don't know the frequency
of the arc itself.


Ron: I had wondered if it was possible that the door had lost contact
(grease in the hinges?) with the chassis and was therefore able to
charge up. It still seems like it would have been easier to jump back
to the chassis than across the gap, but then I have two burn marks, so
maybe it went out into the door and then back to the chassis a ways
down for a while before hand?


Sam: I completely agree with both you and Ron that this seems far-
fetched. It seemed so unlikely that I started think I'd just made up
having seen the arc, and I wouldn't believe it if I didn't have the
burn marks staring me in the face. I also completely agree with your
reasoning for ruling out the HV as the explanation. Even so, I still
have some problems with the load explanation that I need to answer
before I trust my kitchen again. First, and most important, by the
same argument you made ruling out HV problems as the source, shouldn't
any spark created inside the oven by whatever mechanism be contained
by the chassis unless something has gone horribly wrong? On the other
hand, proceeding from the assumption that its impossible for the
entire chassis from floating up high enough to do this, is it even
possible for a load problem to cause a really large arc? In ballpark
figures, the oven is rated at ~1000 watts, the magnetron is some ~50%
efficient, say, so there can't be more than a than a few hundred watts
of microwaves bouncing around, right? Even if you made a tuned
resonator (one of these graphite and aluminum foil gizmos, for
example), and had no other load, is it possible to recover that energy
efficiently enough to something like this? At any rate, to be clear,
nobody thinks that in the absence of other problems I have reason to
doubt my house ground?


Did the fireworks happen *instantly* when you pushed START? Instantly
means in a fraction of a second.

Any effect would have 60 Hz in it since the microwaves are generated in
pulses that have 100 percent ripple at 60 Hz.

Could there be a 2 inch arc from 1000 W of microwaves? Sure.

And a half stick of butter or whatever is probably not a very good
absorber so some sort of peculiar resonant cavity effect is quite
possible. And, if there was dirt, grime, and goop in the area
of the door where the arcing took place, even more possible.

Beyond that, I'd say you have to try some more experiments. :-)

To be sure, check your outlet ground with a multimeter or outlet tester.
But plenty of microwave ovens are used without proper grounds despite the
warnings.

I can't imagine any problem with the house ground that wouldn't result
in other issues.

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.


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Default Sharp microwave arcs *through* front door

About twenty five something years ago, I read a book about the
magnetron.A guy in England had the secret of the magnetron and he was
going from somewhere to somewhere else and he had an armed guard guy
traveling with him.The armed guard guy had orders to shoot and kill the
magnetron guy if he was about to be captured by the enemy.

Another article in that book was something about a Military Aircraft
hanger that was made of wood.(in Germany, I think it was) The Radar
system at that Base in Gemany was making the nails in that hanger glow
red hot and with popping noises too, they wound up having to do some
readjustments with that Radar system.Do you remember the Radar Ranges,
Microwave ovens?
cuhulin

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Default Sharp microwave arcs *through* front door

wrote in message
...

Another article in that book was something about a military aircraft
hanger that was made of wood.(in Germany, I think it was) The radar
system at that base in Gemany was making the nails in that hanger
glow red hot and with popping noises too, they wound up having to
do some readjustments with that radar system.


This is an absurd urban legend.

Microwaves have to be absorbed to heat something. Metallic objects reflect
microwaves and are therefore not heated.

A microwave field with sufficient power to heat nails red-hot (assuming the
nails absorbed the energy, which they don't) would quickly kill any living
thing in that field.




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Default Sharp microwave arcs *through* front door

http://www.southgatearc.org/news/feb..._magnetron.htm

If you are ever in London, say Hello to ''Maggie'' Magnetron for me.
cuhulin
www.incallander.co.uk/music/maggiemp3.wav

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Default Sharp microwave arcs *through* front door

William Sommerwerck wrote:

wrote in message
...

Another article in that book was something about a military aircraft
hanger that was made of wood.(in Germany, I think it was) The radar
system at that base in Gemany was making the nails in that hanger
glow red hot and with popping noises too, they wound up having to
do some readjustments with that radar system.


This is an absurd urban legend.

Microwaves have to be absorbed to heat something. Metallic objects reflect
microwaves and are therefore not heated.

A microwave field with sufficient power to heat nails red-hot (assuming the
nails absorbed the energy, which they don't) would quickly kill any living
thing in that field.



WIlliam, you need to update your 'Skippy" list.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Default Sharp microwave arcs *through* front door

"Michael A. Terrell" wrote in message
...
William Sommerwerck wrote:


wrote in message
...


Another article in that book was something about a military aircraft
hanger that was made of wood.(in Germany, I think it was) The radar
system at that base in Gemany was making the nails in that hanger
glow red hot and with popping noises too, they wound up having to
do some readjustments with that radar system.


This is an absurd urban legend.


Microwaves have to be absorbed to heat something. Metallic objects
reflect microwaves and are therefore not heated.


A microwave field with sufficient power to heat nails red-hot (assuming
the nails absorbed the energy, which they don't) would quickly kill any
living thing in that field.



WIlliam, you need to update your 'Skippy" list.


Perhaps, but that sort of wildly incorrect statement needed explicit
refutation. Someone in this group might have believed it.


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Default Sharp microwave arcs *through* front door

Skippity Doo Da, that old song by what's her name, Skippity Do Da Day.
It's pouring down raining cats and dogs and tree frogs outside
now.Doggy, just now kissed my right ear.(that means she
www.cattledog.com www.acdca.org has to put my dog leash on me and
take me out in the front yard) Let me get my mini brella, old worn out
pith cat hat on.
cuhulin
....................
Donna Fargo?
...................

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Default Sharp microwave arcs *through* front door

incallander.co.uk
About six/seven years ago, Barbara Lynch, from Limerick,Ireland (she
lives in the Hotlanta area) [[forced me]] to dig up the Raglan Road song
for her.Only took me about ten minutes.Barb, you know I am your number
one fan club.
cuhulin



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Default Sharp microwave arcs *through* front door

Chris wrote in news:5a8793cc-df83-4935-b543-
:

Thanks for all the replies. Its beginning to sound like I was right
to feel baffled. Its certainly not mains voltage, but before the arc
there was a buzz that sounded like mains frequency. Since you cant
see a flicker even at 60Hz (I'm in the US), I don't know the frequency
of the arc itself.
....


Thanks again. I'll keep cooking with one hand in my pocket for now.


I would follow the advice of the others and contact the manufacturer
immediately, discontinue use!

Treat the oven like you would a live bomb!!! [Cut the circuit breaker,
unplug the oven, turn the circuit breaker back on]

Supply them with pictures [as best you can reconstruct] the exact
configuration of the oven, its contents, and the rack. Along with diagrams
and pictures of the burn marks.

My best guess as to something that might cause the arcing you observed is
highly unlikely:

1) the vapors from the heated butter [moist air and fat] producing a
conductive path inside the oven that happened to resonant at the magnetron
frequency.
2) The door and the metal rack also forming a resonant circuit.
3) capacitive coupling THROUGH the metal screen built into the door.
4) ionization of the air between the door and the rack, perhaps by a stray
cosmic ray that 'kicked off' the arc.
5) Your house just happened [for a few moments] to be at a point of
resonance in the 60 Hz power grid that covers the country.
Or a resonant, ionized path, within the area around the power transformer
that allowed a similar arc that allowed [intermittently] the 60 Hz HV AC to
jump from transformer to case to rack[there should be burn marks near the
transformer, also.

Question: where did the 'power' go after jumping to the metal rack? Any
'exit wounds'

None of the points seem probable but all seem barely possible.
Comment: YOU are lucky to be alive. Think about that arc jumping to YOU.

I used to fix radars for a living and I have seen some 'odd' things happen,
but nothing as odd as what you described.

--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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