Usual failure modes of magnetrons?

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

 

[Paul Drahn]

On 1/7/2012 7:03 PM, etpm@whidbey.com wrote:

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
Magnetrons are still vacuum tubes with heaters in them. They are

probably made in China and quality control is letting crap out the door.

Paul

 

[mike]

etpm@whidbey.com wrote:

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
How did you measure the "really high voltage going to the magnetron"???

 

[larry moe 'n curly]

e...@whidbey.com wrote:

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.

I think the www.repairFAQ.org has information about diagnosing
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.

 

[Wolfgang Allinger]

On 07 Jan 12 at group /sci/electronics/repair in article
<pdrahn@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

--
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]

etpm@whidbey.com wrote in news:vb1ig7l9hnfpq1jattjg9nt0ca038qautv@4ax.com:

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

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

 

[Paul Drahn]

On 1/8/2012 5:37 AM, Wolfgang Allinger wrote:

On 07 Jan 12 at group /sci/electronics/repair in article
pdrahn@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

assemblies, complete with antenna, by the thousands from China and have
never had a bad one.

Paul

 

[Wolfgang Allinger]

On 08 Jan 12 at group /sci/electronics/repair in article
<pdrahn@webformixair.com> (Paul Drahn) wrote:

On 1/8/2012 5:37 AM, Wolfgang Allinger wrote:
pdrahn@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 :]

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






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.

 

[Roger Jones]

On Jan 7, 10:03 pm, e...@whidbey.com wrote:

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

As someone said, there's not much to go wrong on the power side.
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]

"Paul Drahn"
etpm@whidbey.com wrote:

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 ????

That was the era when Japan and Taiwan were dominant.



..... Phil

 

[Phil Allison]

"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.

Affects lots of valves, big and small.



..... Phil

 

[Winston]

Phil Allison wrote:

"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.

Affects lots of valves, big and small.

I've dissected a few microwave ovens to salvage
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

 

[hrhofmann@att.net]

On Jan 9, 8:39 am, Winston <Wins...@BigBrother.net> wrote:

Phil Allison wrote:
"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.

     Affects lots of valves, big and small.

I've dissected a few microwave ovens to salvage
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

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.

 

[Winston]

hrhofmann@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

 

[klem kedidelhopper]

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

 

[Robert Macy]

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

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

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]

On Jan 10, 10:37 am, Robert Macy <robert.a.m...@gmail.com> wrote:

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



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

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]

On Jan 10, 5:25 pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

On Jan 10, 10:37 am, Robert Macy <robert.a.m...@gmail.com> wrote:





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

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

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]

On Tue, 10 Jan 2012 06:29:34 -0800 (PST), klem kedidelhopper
<captainvideo462009@gmail.com> wrote:

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

The new planned obsolescence.

>?-)

 

On Tuesday, January 10, 2012 at 9:29:34 AM UTC-5, klem kedidelhopper wrote:

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.