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Usual failure modes of magnetrons?

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Robert Macy
Guest

Tue Jan 10, 2012 5:37 pm   



On Jan 10, 7:29am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:
Quote:
On Jan 9, 11:16pm, Winston <Wins...@BigBrother.net> wrote:





hrhofm...@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

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

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

klem kedidelhopper
Guest

Wed Jan 11, 2012 2:25 am   



On Jan 10, 10:37am, Robert Macy <robert.a.m...@gmail.com> wrote:
Quote:
On Jan 10, 7:29am, klem kedidelhopper <captainvideo462...@gmail.com
wrote:



On Jan 9, 11:16pm, Winston <Wins...@BigBrother.net> wrote:

hrhofm...@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

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

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

So the "lesson" is: don't throw out your old stuff. Maintain it as
long as you can because, (and sadly), "they just don't make em like
that any more".....Lenny

Robert Macy
Guest

Wed Jan 11, 2012 8:12 pm   



On Jan 10, 5:25pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:
Quote:
On Jan 10, 10:37am, Robert Macy <robert.a.m...@gmail.com> wrote:





On Jan 10, 7:29am, klem kedidelhopper <captainvideo462...@gmail.com
wrote:

On Jan 9, 11:16pm, Winston <Wins...@BigBrother.net> wrote:

hrhofm...@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

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

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

So the "lesson" is: don't throw out your old stuff. Maintain it as
long as you can because, (and sadly), "they just don't make em like
that any more".....Lenny

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!

josephkk
Guest

Sat Jan 14, 2012 4:03 am   



On Tue, 10 Jan 2012 06:29:34 -0800 (PST), klem kedidelhopper
<captainvideo462009_at_gmail.com> wrote:

Quote:
On Jan 9, 11:16pm, Winston <Wins...@BigBrother.net> wrote:
hrhofm...@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

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

The new planned obsolescence.

>?-)


Guest

Thu Apr 02, 2020 1:45 am   



On Tuesday, January 10, 2012 at 9:29:34 AM UTC-5, klem kedidelhopper wrote:
Quote:
On Jan 9, 11:16 pm, Winston <Wins...@BigBrother.net> wrote:
hrhofm...@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

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


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? Thanks in advance.

Phil Allison
Guest

Thu Apr 02, 2020 4:45 am   



kevin.k...@gmail.com wrote:

----------------------------

Quote:

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
Guest

Thu Apr 02, 2020 6:45 am   



On 2020/04/01 8:23 p.m., Phil Allison wrote:
Quote:
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




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
Guest

Thu Apr 02, 2020 3:45 pm   



On Thursday, April 2, 2020 at 1:36:22 AM UTC-4, John Robertson wrote:

Quote:
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.

Phil Hobbs
Guest

Thu Apr 02, 2020 4:45 pm   



On 2020-04-02 10:38, John-Del wrote:
Quote:
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.


You can still stick a knife in the interlock if you need to fry
somebody's intruding drone. ;)

Cheers

Phil Hobbs

pfjw@aol.com
Guest

Thu Apr 02, 2020 4:45 pm   



On Thursday, April 2, 2020 at 10:47:20 AM UTC-4, Phil Hobbs wrote:

Quote:
You can still stick a knife in the interlock if you need to fry
somebody's intruding drone. Wink


Total immersion is simpler. Add a bit of salt or baking soda to the water, that makes the damage irreparable.

Peter Wieck
Melrose Park, PA


Guest

Fri Apr 03, 2020 11:45 am   



On Thursday, 2 April 2020 06:36:22 UTC+1, John Robertson wrote:
Quote:
On 2020/04/01 8:23 p.m., Phil Allison wrote:
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




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 :-#)#


Door switches take more than a few amps, and that still applies to a lot of current prodution units.

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
Guest

Fri Apr 03, 2020 1:45 pm   



On 03/04/2020 21:28, tabbypurr_at_gmail.com wrote:
Quote:
On Thursday, 2 April 2020 06:36:22 UTC+1, John Robertson wrote:
On 2020/04/01 8:23 p.m., Phil Allison wrote:
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




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 :-#)#

Door switches take more than a few amps, and that still applies to a lot of current prodution units.

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


I saw an interesting very old Moulinex one which seemed to have a fairly
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
Guest

Fri Apr 03, 2020 5:45 pm   



On 2020-04-02 11:05, pfjw_at_aol.com wrote:
Quote:
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.

Peter Wieck
Melrose Park, PA

You have to catch it first though.


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.
Guest

Mon Apr 13, 2020 2:45 am   



tabbypurr_at_gmail.com 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.

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:Paul_at_Hovnanian.com
------------------------------------------------------------------
Someone figured out my password. Now I have to rename my dog.


Guest

Wed Apr 15, 2020 1:45 am   



On Monday, 13 April 2020 02:13:34 UTC+1, Paul Hovnanian P.E. wrote:
Quote:
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

Quote:
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

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