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Usual failure modes of magnetrons?
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et...@whidbey.com
Jan 7, 2012, 10:03:43 PM1/7/12
to
Greetings All,
I have a Sharp brand "Half Pint" 400 watt microwave oven my wife and I
bought new in 1986. The thing still works like new. I use it now in
my shop because we have bought more powerful microwave ovens over the
years to use in our house. We have bought more than one because the
magnetrons in the others failed. At least I think the magnetrons
failed because there was still really high voltage going to the
magnetrons and the other oven functions worked (timer, digital
display, etc.). So I was wondering why my old Sharp Half Pint oven
still works and how magnetrons failed.
Thanks,
Eric
I have a Sharp brand "Half Pint" 400 watt microwave oven my wife and I
bought new in 1986. The thing still works like new. I use it now in
my shop because we have bought more powerful microwave ovens over the
years to use in our house. We have bought more than one because the
magnetrons in the others failed. At least I think the magnetrons
failed because there was still really high voltage going to the
magnetrons and the other oven functions worked (timer, digital
display, etc.). So I was wondering why my old Sharp Half Pint oven
still works and how magnetrons failed.
Thanks,
Eric
Paul Drahn
Jan 7, 2012, 10:50:26 PM1/7/12
to
probably made in China and quality control is letting crap out the door.
Paul
larry moe 'n curly
Jan 8, 2012, 7:32:13 AM1/8/12
to
microwave ovens.
I had one magnetron fail when its permanent magnet (3" or so disk with
a large hole in the middle) cracked, and another one developed a short
in one of its feed-through capacitors where the high voltage went into
it.
mike
Jan 8, 2012, 8:00:48 AM1/8/12
to
Wolfgang Allinger
Jan 8, 2012, 8:37:00 AM1/8/12
to
On 07 Jan 12 at group /sci/electronics/repair in article
<pdr...@webformixair.com> (Paul Drahn) wrote:
>Magnetrons are still vacuum tubes with heaters in them.
>They are probably made in China and quality control is letting crap out
>the door.
Sorry, you are wrong. CE aka China Engineering aka Crap Enforcement
>Magnetrons are still vacuum tubes with heaters in them.
>They are probably made in China and quality control is letting crap out
>the door.
doesn`t let quality in, so there is no quality production :]
Saludos Wolfgang
--
Wolfgang Allinger 15h00..21h00 MEZ: SKYPE:wolfgang.allinger
Paraguay mailer: CrossPoint XP 3.20 (XP2) in WinXPprof DOSbox
Meine 7 Sinne: reply Adresse gesetzt!
Unsinn, Schwachsinn, Bloedsinn, Wahnsinn, Stumpfsinn, Irrsinn, Loetzinn.
Jim Yanik
Jan 8, 2012, 4:11:47 PM1/8/12
to
et...@whidbey.com wrote in news:vb1ig7l9hnfpq1jat...@4ax.com:
usually,the MW output drops,perhaps from reduced cathode emission.
or the filament opens,they don't last forever. :-)
or internal arcing causes the PS fuse to blow.
Not much else to go wrong.
--
Jim Yanik
jyanik
at
localnet
dot com
or the filament opens,they don't last forever. :-)
or internal arcing causes the PS fuse to blow.
Not much else to go wrong.
--
Jim Yanik
jyanik
at
localnet
dot com
Paul Drahn
Jan 8, 2012, 4:42:36 PM1/8/12
to
On 1/8/2012 5:37 AM, Wolfgang Allinger wrote:
> On 07 Jan 12 at group /sci/electronics/repair in article
> <pdr...@webformixair.com> (Paul Drahn) wrote:
>
>> Magnetrons are still vacuum tubes with heaters in them.
>
>> They are probably made in China and quality control is letting crap out
>> the door.
>
> Sorry, you are wrong. CE aka China Engineering aka Crap Enforcement
> doesn`t let quality in, so there is no quality production :]
>
>
>
> Saludos Wolfgang
>
Yes, that is true, in some cases. On the other hand, I buy GPS receiver
> On 07 Jan 12 at group /sci/electronics/repair in article
> <pdr...@webformixair.com> (Paul Drahn) wrote:
>
>> Magnetrons are still vacuum tubes with heaters in them.
>
>> They are probably made in China and quality control is letting crap out
>> the door.
>
> Sorry, you are wrong. CE aka China Engineering aka Crap Enforcement
> doesn`t let quality in, so there is no quality production :]
>
>
>
> Saludos Wolfgang
>
assemblies, complete with antenna, by the thousands from China and have
never had a bad one.
Paul
Wolfgang Allinger
Jan 8, 2012, 5:45:00 PM1/8/12
to
On 08 Jan 12 at group /sci/electronics/repair in article
>> <pdr...@webformixair.com> (Paul Drahn) wrote:
>>> They are probably made in China and quality control is letting crap
>>> out the door.
>>
>> Sorry, you are wrong. CE aka China Engineering aka Crap Enforcement
>> doesn`t let quality in, so there is no quality production :]
>>
>>> They are probably made in China and quality control is letting crap
>>> out the door.
>>
>> Sorry, you are wrong. CE aka China Engineering aka Crap Enforcement
>> doesn`t let quality in, so there is no quality production :]
>>
>Yes, that is true, in some cases. On the other hand, I buy GPS
>receiver assemblies, complete with antenna, by the thousands from
>China and have never had a bad one.
Good to hear, that not every product is controlled by Crap Enforcement
>receiver assemblies, complete with antenna, by the thousands from
>China and have never had a bad one.
:)
Roger Jones
Jan 8, 2012, 5:58:32 PM1/8/12
to
Magnetron can fail, either catastrophically or go low gain and not
oscillate. There's a HV transformer with a pile-wound secondary that
could short out (likely blowing a fuse) and a voltage doubler diode/
capacitor that could fail (either, but a cap failure would take out
the diode.)
See http://www.gallawa.com/microtech/dataselect.html
Safety! Microwave oven can give lethal electric shocks! Never try to
measure ANY voltages while oven is ON. Always discharge the HV
capacitor before touching ANY connection in the MW oven. See safety
note on above website.
If you don't know what you are doing, DON'T try to fix MW ovens.
Cheers,
Roger
Phil Allison
Jan 8, 2012, 9:42:42 PM1/8/12
to
"Paul Drahn"
et...@whidbey.com wrote:
>>
>> I have a Sharp brand "Half Pint" 400 watt microwave oven my wife and I
>> bought new in 1986.
>
>>
>> I have a Sharp brand "Half Pint" 400 watt microwave oven my wife and I
>> bought new in 1986.
>
> Magnetrons are still vacuum tubes with heaters in them. They are probably
> made in China and quality control is letting crap out the door.
** Magnetrons for Sharp microwave ovens made in China back in 1986 ????
> made in China and quality control is letting crap out the door.
That was the era when Japan and Taiwan were dominant.
.... Phil
Phil Allison
Jan 9, 2012, 5:54:08 AM1/9/12
to
"Jim Yanik"
>
>
> usually,the MW output drops,perhaps from reduced cathode emission.
> or the filament opens,they don't last forever. :-)
> or internal arcing causes the PS fuse to blow.
>
> Not much else to go wrong.
** Must be some cases of loss of vacuum.
>
> usually,the MW output drops,perhaps from reduced cathode emission.
> or the filament opens,they don't last forever. :-)
> or internal arcing causes the PS fuse to blow.
>
> Not much else to go wrong.
Affects lots of valves, big and small.
.... Phil
Winston
Jan 9, 2012, 9:39:56 AM1/9/12
to
transformers and for fun.
I've found cracked magnets on a few magnetrons.
I don't know if a cracked magnet would cause the
failure of a magnetron, if that was the root cause
of the failures or if some other failure caused
the magnets to crack.
--Winston
hrho...@att.net
Jan 9, 2012, 10:28:15 AM1/9/12
to
transformer. Never seen a cracked magnet. But those old magnets are
great for fooling around with as they ar so strong.
Winston
Jan 9, 2012, 11:16:31 PM1/9/12
to
hrho...@att.net wrote:
(...)
> Every one I have ever salvaged had low magnetron output or a bad HV
> transformer. Never seen a cracked magnet. But those old magnets are
> great for fooling around with as they ar so strong.
I wonder if a cracked magnet could cause low microwave
output?
Sounds like a chicken and egg problem.
Excessive power dissipation in the magnetron might
cause a magnet to crack. (Line transient perhaps?)
The cracked magnet would push the magnetron
away from cutoff, forcing it to dissipate more
power which heats the magnets, etc.
--Winston
(...)
> Every one I have ever salvaged had low magnetron output or a bad HV
> transformer. Never seen a cracked magnet. But those old magnets are
> great for fooling around with as they ar so strong.
output?
Sounds like a chicken and egg problem.
Excessive power dissipation in the magnetron might
cause a magnet to crack. (Line transient perhaps?)
The cracked magnet would push the magnetron
away from cutoff, forcing it to dissipate more
power which heats the magnets, etc.
--Winston
klem kedidelhopper
Jan 10, 2012, 9:29:34 AM1/10/12
to
On Jan 9, 11:16 pm, Winston <Wins...@BigBrother.net> wrote:
Like you we have a small Goldstar oven that we got as an incentive for
visiting a time share back around 1985. The thing has a simple wind up
clock timer that rings a bell when it runs down. It too has worked
flawlessly all these years. I've been repairing consumer electronics
all my life and although I've never heard the term before I firmly
believe that "crap engineering" is in everything today and is
definitely alive and well in China. Lenny
visiting a time share back around 1985. The thing has a simple wind up
clock timer that rings a bell when it runs down. It too has worked
flawlessly all these years. I've been repairing consumer electronics
all my life and although I've never heard the term before I firmly
believe that "crap engineering" is in everything today and is
definitely alive and well in China. Lenny
Robert Macy
Jan 10, 2012, 10:37:41 AM1/10/12
to
On Jan 10, 7:29 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:
I'm old enough to remember when we used to pick up a 'broken' item and
pretend to read a label on it, musing out loud, "Oh, I see what's
wrong. MADE IN JAPAN." ThenJapan got their act together and became one
of the best suppliers of high quality opticselectronics/musical
instruments.
So, ...the lesson? it is apparently far easier to continue to make
things cheap, but learn how to make them well rather than continue to
make things well, but learn how to make them cheap. Shudder
wrote:
pretend to read a label on it, musing out loud, "Oh, I see what's
wrong. MADE IN JAPAN." ThenJapan got their act together and became one
of the best suppliers of high quality opticselectronics/musical
instruments.
So, ...the lesson? it is apparently far easier to continue to make
things cheap, but learn how to make them well rather than continue to
make things well, but learn how to make them cheap. Shudder
klem kedidelhopper
Jan 10, 2012, 7:25:08 PM1/10/12
to
long as you can because, (and sadly), "they just don't make em like
that any more".....Lenny
Robert Macy
Jan 11, 2012, 1:12:36 PM1/11/12
to
On Jan 10, 5:25 pm, klem kedidelhopper <captainvideo462...@gmail.com>
True. You're talking to a guy that spent 3 hours to fix an $8
hairdryer. The hairdryer worked longer after the 'fix' than it did
between purchase and failure.
Same with a repaired Hamilton Beach Brew Station Deluxe Coffee
Machine. Originally a company had it in service for 1 year, it broke,
they 'threw' it away. I repaired it and it has been working in our
firm for over two years and is still going!
hairdryer. The hairdryer worked longer after the 'fix' than it did
between purchase and failure.
Same with a repaired Hamilton Beach Brew Station Deluxe Coffee
Machine. Originally a company had it in service for 1 year, it broke,
they 'threw' it away. I repaired it and it has been working in our
firm for over two years and is still going!
josephkk
Jan 13, 2012, 10:03:04 PM1/13/12
to
>?-)
kevin.kb...@gmail.com
Apr 1, 2020, 8:36:48 PM4/1/20
to
A repairman once told me that opening the door before the timer stopped the operation was bad for the magnetron. He said the unexpected interruption was a shock that over time led to more frequent magnetron failures. Do you have any knowledge or opinion about this? Thanks in advance.
Phil Allison
Apr 1, 2020, 11:23:02 PM4/1/20
to
kevin.k...@gmail.com wrote:
----------------------------
>
> Hey Lenny,
>
> A repairman once told me that opening the door before the timer stopped the operation was bad for the magnetron. He said the unexpected interruption was a shock that over time led to more frequent magnetron failures. Do you have any knowledge or opinion about this?
-----------------------------------------------------
** There are hundreds of bullshit myths like this put around to blame users for failures that were nothing to do with them.
It a variation on the "blame the victim" logic.
Used when the real culprit desperately needs an excuse.
Or a supplier want to avoid a valid warranty claim.
Never fall for it.
.... Phil
----------------------------
>
> Hey Lenny,
>
> A repairman once told me that opening the door before the timer stopped the operation was bad for the magnetron. He said the unexpected interruption was a shock that over time led to more frequent magnetron failures. Do you have any knowledge or opinion about this?
** There are hundreds of bullshit myths like this put around to blame users for failures that were nothing to do with them.
It a variation on the "blame the victim" logic.
Used when the real culprit desperately needs an excuse.
Or a supplier want to avoid a valid warranty claim.
Never fall for it.
.... Phil
John Robertson
Apr 2, 2020, 1:36:22 AM4/2/20
to
>
>
>
I agree with Phil.
The only thing I could see having a problem when you open the door prior
to the microwave timed out is the actual door safety switch, and only if
it carried a few amps of current - perhaps so on early microwaves. A
simple signal switch doesn't care much if the current is micro-amps it
will last as long as it would with no power. X number of door openings -
typically a million or so for a good quality switch.
The magnetron wouldn't care either, it has a certain number of ON
(powered up) hours in it, and considering the cycling the magnetron does
on reduced heating times, then that too is quite a long time - for
better quality units.
I've not seen the schematics for a microwave, but I assume that sensible
safety requirements would have at least two switches to disable the
magnetron if the door was opened when operating.
When I bought out our local TV/VCR/small appliance parts shop last year
there was also a bunch of microwave parts - magnetrons, big caps, etc. I
really should put them up on my site in case someone wants to fix older
units. Really, someone might want to!
John :-#)#
John-Del
Apr 2, 2020, 10:38:41 AM4/2/20
to
On Thursday, April 2, 2020 at 1:36:22 AM UTC-4, John Robertson wrote:
> I've not seen the schematics for a microwave, but I assume that sensible
> safety requirements would have at least two switches to disable the
> magnetron if the door was opened when operating.
>
Later generations have them wired in a make/break situation so in case a switch sticks closed or is intentionally jumped out, it shorts the supply and blows the main fuse.
> I've not seen the schematics for a microwave, but I assume that sensible
> safety requirements would have at least two switches to disable the
> magnetron if the door was opened when operating.
>
Phil Hobbs
Apr 2, 2020, 10:47:20 AM4/2/20
to
somebody's intruding drone. ;)
Cheers
Phil Hobbs
peterw...@gmail.com
Apr 2, 2020, 11:05:19 AM4/2/20
to
On Thursday, April 2, 2020 at 10:47:20 AM UTC-4, Phil Hobbs wrote:
> You can still stick a knife in the interlock if you need to fry
> somebody's intruding drone. ;)
>
Total immersion is simpler. Add a bit of salt or baking soda to the water, that makes the damage irreparable.
> You can still stick a knife in the interlock if you need to fry
> somebody's intruding drone. ;)
>
Peter Wieck
Melrose Park, PA
tabb...@gmail.com
Apr 3, 2020, 6:28:30 AM4/3/20
to
Microwave interlocks use 4 switches in a self monitoring configuration. If a switch should open but doesn't, another monitoring switch shorts the power feed (via a resistor) which blows the main fuse. 2 series switches without monitoring were used in the 1970s. I've seen much worse in historic machines, I remember one that continued cooking with the door part way open.
NT
Chris Jones
Apr 3, 2020, 8:00:22 AM4/3/20
to
loose door, but when it started cooking, an electromagnet pulled the
door very tightly onto the oven. Before I tried it, I expected it to be
very leaky but it was one of the least leaky I tested.
Phil Hobbs
Apr 3, 2020, 12:07:31 PM4/3/20
to
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Paul Hovnanian P.E.
Apr 12, 2020, 9:13:34 PM4/12/20
to
I'm looking ata schematic from an old Sharp microwave. There is such a
'monitor switch' which shorts the power supply. It is located immediately
across the magnetron primary. So, should al other interlocks and control
relays fail, this will indeed blow the fuse.
Now, back to the original rumor. Should someone open the door on the oven
rather then wait for the control to shut off power, that short may be
applied to the transformer before it and/or the magnetron has bled off
energy. The resulting transient might be enough to shorten the life on
something.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Someone figured out my password. Now I have to rename my dog.
'monitor switch' which shorts the power supply. It is located immediately
across the magnetron primary. So, should al other interlocks and control
relays fail, this will indeed blow the fuse.
Now, back to the original rumor. Should someone open the door on the oven
rather then wait for the control to shut off power, that short may be
applied to the transformer before it and/or the magnetron has bled off
energy. The resulting transient might be enough to shorten the life on
something.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Someone figured out my password. Now I have to rename my dog.
tabb...@gmail.com
Apr 14, 2020, 8:29:56 PM4/14/20
to
On Monday, 13 April 2020 02:13:34 UTC+1, Paul Hovnanian P.E. wrote:
> Now, back to the original rumor. Should someone open the door on the oven
> rather then wait for the control to shut off power, that short may be
> applied to the transformer before it and/or the magnetron has bled off
> energy. The resulting transient might be enough to shorten the life on
> something.
The short only occurs if the primary interlock switches fail, no other situation. At which point no-one cares what it does to equipment life expectancy.
NT
> tabbypurr wrote:
>
> > another monitoring switch shorts the power feed
>
> I'm looking ata schematic from an old Sharp microwave. There is such a
> 'monitor switch' which shorts the power supply. It is located immediately
> across the magnetron primary. So, should al other interlocks and control
> relays fail, this will indeed blow the fuse.
that's the plan
>
> > another monitoring switch shorts the power feed
>
> I'm looking ata schematic from an old Sharp microwave. There is such a
> 'monitor switch' which shorts the power supply. It is located immediately
> across the magnetron primary. So, should al other interlocks and control
> relays fail, this will indeed blow the fuse.
> Now, back to the original rumor. Should someone open the door on the oven
> rather then wait for the control to shut off power, that short may be
> applied to the transformer before it and/or the magnetron has bled off
> energy. The resulting transient might be enough to shorten the life on
> something.
NT
Paul Hovnanian P.E.
Apr 16, 2020, 3:55:35 PM4/16/20
to
tabb...@gmail.com wrote:
>
> The short only occurs if the primary interlock switches fail, no other
> situation. At which point no-one cares what it does to equipment life
> expectancy.
The shorting monitor switch closes every time the door opens. If the timer
>
> The short only occurs if the primary interlock switches fail, no other
> situation. At which point no-one cares what it does to equipment life
> expectancy.
shuts off the magnetron and you open the door a few seconds later, there is
no effect. If you open the door on a running oven, even if the series
interlock switch removes AC power from the HV transformer, the shorting
switch may close within milliseconds of that. So what is the time constant
of the decaying field in the transformer? And what hapens if you give that
field a shorted winding?
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Cydrome Leader
Apr 23, 2020, 1:44:42 AM4/23/20
to
Paul Hovnanian P.E. <pa...@hovnanian.com> wrote:
> tabb...@gmail.com wrote:
>
>>
>> The short only occurs if the primary interlock switches fail, no other
>> situation. At which point no-one cares what it does to equipment life
>> expectancy.
>
> The shorting monitor switch closes every time the door opens. If the timer
> shuts off the magnetron and you open the door a few seconds later, there is
> no effect. If you open the door on a running oven, even if the series
> interlock switch removes AC power from the HV transformer, the shorting
> switch may close within milliseconds of that. So what is the time constant
> of the decaying field in the transformer? And what hapens if you give that
> field a shorted winding?
The delay in the mechanical timing of those switches is clearly always enough. If there
> tabb...@gmail.com wrote:
>
>>
>> The short only occurs if the primary interlock switches fail, no other
>> situation. At which point no-one cares what it does to equipment life
>> expectancy.
>
> The shorting monitor switch closes every time the door opens. If the timer
> shuts off the magnetron and you open the door a few seconds later, there is
> no effect. If you open the door on a running oven, even if the series
> interlock switch removes AC power from the HV transformer, the shorting
> switch may close within milliseconds of that. So what is the time constant
> of the decaying field in the transformer? And what hapens if you give that
> field a shorted winding?
was overlap, you'd blow the fuse every time.
fun fact, the monitor swtich as it's being called here is these days (at least the past
decade if not longer) is a non-snap action switch in a standard microswitch form factor.
The only rating is 1 use and enough current to blow the mains fuse. They never switch any
load during the life of the microwave unless there is a fault condition. Microwave ovens
are sort of like cars and have every possible extra cost engineered out. Polaroid instant
cameras were like that too. It was amazing how many parts they tweaked out of the design.
three_jeeps
Apr 24, 2020, 7:39:26 AM4/24/20
to
Link points to a website that is under construction???
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