Microwave oven

[Sam Goldwasser]

"Retired" <everettlarsen@sbcglobal.net> writes:

I have a GE microwave oven that just stopped heating. I have checked
and found the problem to be in the high voltage section. I found the
high voltage diode shorted and the high voltage capacitor going bad.

What do you mean by "going bad"?

I've replaced both of these, but it still does not heat. When I
rechecked I again found the diode shorted within 1 minute of running.

Was it heating during that 1 minute?

The magnetron tube was replace 3 months ago and the transformer tests
good. The magnetron tube show no short to case. Also no shorts in
transformer, and correct ohms on each winding. Has anyone run into
this, or have any ideas?
Retired

There's only 4 parts there - HV transformer, HV capacitor, HV diode,
magnetron. It's unlikely that the HV transformer could go bad in a
way that would not result in a blown fuse or lots of smoke.

The magnetron could be defective and show up only with HV applied.

What abouut the condition of the waveguide and the rest of the oven?

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[Retired]

The capacitor showed a short to case after running for about 2
minutes, but would again test OK after being off for a while. The wave
guide and the rest of the oven look A1. The magentron look good also.
No ;I got no heat in that 1 minute that I ran it. I had a cup of water
in it, and it stayed cold. I am beganning to think it is the magnetron
even though I can not prove it.

 

[Retired]

The capacitor showed a short to case after running for about 2
minutes, but would again test OK after being off for a while. The wave
guide and the rest of the oven look A1. The magentron look good also.
No ;I got no heat in that 1 minute that I ran it. I had a cup of water
in it, and it stayed cold. I am beganning to think it is the magnetron
even though I can not prove it.

 

[Retired]

The capacitor showed a short to case after running for about 2
minutes, but would again test OK after being off for a while. The wave
guide and the rest of the oven look A1. The magentron look good also.
No ;I got no heat in that 1 minute that I ran it. I had a cup of water
in it, and it stayed cold. I am beganning to think it is the magnetron
even though I can not prove it.

 

[Retired]

I have a GE microwave oven that just stopped heating. I have checked
and found the problem to be in the high voltage section. I found the
high voltage diode shorted and the high voltage capacitor going bad.
I've replaced both of these, but it still does not heat. When I
rechecked I again found the diode shorted within 1 minute of running.
The magnetron tube was replace 3 months ago and the transformer tests
good. The magnetron tube show no short to case. Also no shorts in
transformer, and correct ohms on each winding. Has anyone run into
this, or have any ideas?
Retired

 

[JANA]

It sounds like the magnetron is shorting or pulling too much current when it
is powered up.

Is for myself personaly, when my personal microwave oven fails, if it is not
a small easy fault to service, I replace the complete oven. Many of the
models now carry a 3 year warranty. If you amortize the cost over the 3 year
period, the cost is very cheap.

--

JANA
_____


"Retired" <everettlarsen@sbcglobal.net> wrote in message
news:1145273864.726870.145830@u72g2000cwu.googlegroups.com...
I have a GE microwave oven that just stopped heating. I have checked
and found the problem to be in the high voltage section. I found the
high voltage diode shorted and the high voltage capacitor going bad.
I've replaced both of these, but it still does not heat. When I
rechecked I again found the diode shorted within 1 minute of running.
The magnetron tube was replace 3 months ago and the transformer tests
good. The magnetron tube show no short to case. Also no shorts in
transformer, and correct ohms on each winding. Has anyone run into
this, or have any ideas?
Retired

 

[BR]

On 17 Apr 2006 06:40:14 -0700, "Retired" <everettlarsen@sbcglobal.net>
wrote:

The capacitor showed a short to case after running for about 2
minutes, but would again test OK after being off for a while. The wave
guide and the rest of the oven look A1. The magentron look good also.
No ;I got no heat in that 1 minute that I ran it. I had a cup of water
in it, and it stayed cold. I am beganning to think it is the magnetron
even though I can not prove it.

I used to fix them years ago. I made a resistive divider which I could
use to measure the high voltage at the cathode using a conventional
voltmeter. If the heater windings are OK and the voltage is about 2500
(IIRC) then replace the magnetron.

Cheers.

Bill.

 

[GregS]

In article <bIOdnXmHgJ_gWmLVnZ2dnUVZ_hudnZ2d@comcast.com>, "William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

It appears that our microwave oven has lost cooking/heating power over
the
years. Is that possible: Can the magnetron put out less power as it ages?
How can one test the heating power of a microwave oven: Perhaps by
heating
a known quantity of water to a desired rise in temperature over a
prescribed
time period? Are there any such measures for a microwave oven of a known
original/rated power?

It's not a magnetron, it's a klystron. It's a tube and tubes get weak.
But more likely, one of the power sources has become weak.

I don't know where you get your information, but microwave ovens use
magentrons. A klystron is a rather different sort of microwave device. For
one thing, it's an amplifier, not an oscillator (unless you misalign it,
especially the B cavity).

I know about these things, because I used to install and align klystrons. I
could tell you a few "Jedi tricks".

I suppose they still use Klystrons as deep space power amplifiers such as in Apollo missions.
I think the standard power was 20 KW and made by Collins. A Hydrogen Maser
was also used as a low noise amplifier and was used as the primary frequency
standard, Cesium second. I just updated my learning from the web. A Cesium
standard is basically a Xtal oscillator buffered with a atomic feedback loop and
has poor short term stability. The Maser has the best short term stability and porr long term.

greg

 

[Michael A. Terrell]

GregS wrote:

I suppose they still use Klystrons as deep space power amplifiers such as in Apollo missions.
I think the standard power was 20 KW and made by Collins. A Hydrogen Maser
was also used as a low noise amplifier and was used as the primary frequency
standard, Cesium second. I just updated my learning from the web. A Cesium
standard is basically a Xtal oscillator buffered with a atomic feedback loop and
has poor short term stability. The Maser has the best short term stability and porr long term.

greg

Klystrons & Klystrodes were common in UHF aTV transmitters. The last
I used were a set of 65 kW, made by EEV on us Ch. 55. They are being
replaced by solids state transmitters.


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[William Sommerwerck]

I suppose they still use klystrons as deep-space power amplifiers
such as in Apollo missions.

The Apollo mission was not "deep space". Nevertheless, I installed several
Varian klystrons in NASA's STDN.

 

[GregS]

In article <07-dnep7G4jQiJzUnZ2dnUVZ_uqdnZ2d@comcast.com>, "William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

I suppose they still use klystrons as deep-space power amplifiers
such as in Apollo missions.

The Apollo mission was not "deep space". Nevertheless, I installed several
Varian klystrons in NASA's STDN.

Well the moon was a bit farther away. I don't remember what things
were tracked by the maser. Maybe it was just a backup, but easily overloaded
on strong signals. All the 3 main 85 foot MSFN/STDN stations had masers.
After Apollo, ERTS or Landsat was the main preoccupation. Tracking the
Alsep packages on the moon was also done for a VLBI experiment.
After that the stations were also recording Helios orbiting the Sun, a
very week signal. You really had to play with it to get phase lock.

Here is a link to the NASA bible for the stations. Its a big file....
http://zekfrivolous.com/nasa/NASA-SP-87.pdf

greg

 

[Arfa Daily]

"Richard G. Gould" <rickgould@verizon.net> wrote in message
news:RRwKk.2054$Rx2.1950@nwrddc01.gnilink.net...

It appears that our microwave oven has lost cooking/heating power over the
years. Is that possible: Can the magnetron put out less power as it
ages? How can one test the heating power of a microwave oven: Perhaps by
heating a known quantity of water to a desired rise in temperature over a
prescribed time period? Are there any such measures for a microwave oven
of a known original/rated power?

Rick

The waveguide on the output of the mag (and it is a mag - ignore what
clodhopper says below about it being a klystron) can become coated with
resolidified vapourised grease and clag from the food that's been cooked in
it - especially if it is a combination type that has a conventional oven in
it as well. This can result in substantially reduced microwave cooking
efficiency.

Arfa

 

[Ron Johnson]

Arfa Daily wrote:

"Richard G. Gould" <rickgould@verizon.net> wrote in message
news:RRwKk.2054$Rx2.1950@nwrddc01.gnilink.net...
It appears that our microwave oven has lost cooking/heating power over the
years. Is that possible: Can the magnetron put out less power as it
ages? How can one test the heating power of a microwave oven: Perhaps by
heating a known quantity of water to a desired rise in temperature over a
prescribed time period? Are there any such measures for a microwave oven
of a known original/rated power?

Rick


The waveguide on the output of the mag (and it is a mag - ignore what
clodhopper says below about it being a klystron) can become coated with
resolidified vapourised grease and clag from the food that's been cooked in
it - especially if it is a combination type that has a conventional oven in
it as well. This can result in substantially reduced microwave cooking
efficiency.

Absobloominglutely

The first thing to do with an oven which appears to have lost
perfomance, is to give the cavity a good clean, including the inside
glass of the door and the waveguide cover and to check that there`s no
nasty carbonised gunk up the waveguide. Simply replacing the waveguide
cover perks them up a bit.

It`s also important to check the spade connectors on the magnetron,
these sometimes become loose and erode away making intermittent contact
for the heater current. My own Panasonic was suffering from this - about
one in four cookings would fail, replacing the spade connectors cured
the problem.

It is possible (IME) for magnetrons to lose power over time, sometimes
the antenna cap gets eroded away and sometimes you find cracks in one of
the magnets.

Ron

 

[Baron]

Ron Johnson wrote:

It is possible (IME) for magnetrons to lose power over time, sometimes
the antenna cap gets eroded away and sometimes you find cracks in one
of the magnets.

Ron

Yes they do loose power over time ! It depends upon how fast the
filament/cathode looses the ability to produce electrons. Often
Thoriated Tungsten is used in the heater ! If it gets hammered it
rapidly looses emission.

--
Best Regards:
Baron.