Does my microwave diode look good to you?

[Danny D.]

I just tested my microwave diode where, unfortunately, it seems to be good:
http://farm8.staticflickr.com/7358/9594179589_09dac4708b_o.fig

Forward biased with a 9 VDC battery, I measure 7 VDC across the diode;
reverse biased, I read 9 VDC across the diode (given a 200 ohm
current-limiting resistance in series with the battery).

I was hoping the diode was bad, because otherwise, I don't know what's
wrong with the microwave. It does everything but heat up the food.

It makes noise, the lights light up fine, the controls all work,
and it beeps when done, etc. - but it just won't heat up anything.

Did I test the diode properly?

 

[Danny D.]

On Mon, 26 Aug 2013 04:18:18 +0000, Danny D. wrote:

I just tested my microwave diode where, unfortunately, it seems to be good:
http://farm8.staticflickr.com/7358/9594179589_09dac4708b_o.fig

Ooops.
http://farm8.staticflickr.com/7358/9594179589_09dac4708b_o.gif

 

[ChairMan]

Danny D. <dannyd@is.invalid> wrote:

I just tested my microwave diode where, unfortunately, it
seems to be
good:
http://farm8.staticflickr.com/7358/9594179589_09dac4708b_o.fig

Forward biased with a 9 VDC battery, I measure 7 VDC
across the diode;
reverse biased, I read 9 VDC across the diode (given a 200
ohm
current-limiting resistance in series with the battery).

I was hoping the diode was bad, because otherwise, I don't
know what's
wrong with the microwave. It does everything but heat up
the food.

It makes noise, the lights light up fine, the controls all
work,
and it beeps when done, etc. - but it just won't heat up
anything.

Did I test the diode properly?

if it does everything but heat it might be the magnatron
http://www.ehow.com/info_8231169_can-magnetrons-replaced-microwaves.html

 

[micky]

On Mon, 26 Aug 2013 04:18:18 +0000 (UTC), "Danny D."
<dannyd@is.invalid> wrote:

I just tested my microwave diode where, unfortunately, it seems to be good:
see other post for picture.

Forward biased with a 9 VDC battery, I measure 7 VDC across the diode;

reverse biased, I read 9 VDC across the diode (given a 200 ohm
current-limiting resistance in series with the battery).

Since apparently there is no current in that direction, how about
taking out the resistor and seeing what it says then?

I was hoping the diode was bad***, because otherwise, I don't know what's
wrong with the microwave. It does everything but heat up the food.

Normally I'd say you should measure the voltages while it's in the
circuit. That's a little different here since you'd have to have the
cover off and that would expose you to a lot of microwaves. OTOH,
it's not working so maybe there are no microwaves. I hate to rely on
maybe. Do you have a microwave detector. I got one at Radio Shack
about 30 years ago and it works well. I was able to test it because
at that time I had Amana Model 2, and it didn't have door latches on
it. So I could open the door a little before the safety switches
turned the machine off, and I could see the detector reading rise from
zero to at least half way across the scale (but I only allowed that
for a second.) After that, I could check door leakage. RS doesn't
still sell them iirc but you might find one used, or you might find a
new one sold through another channel.

Here's exactly the same one I have, no bids yet, 18 hours left from my
post time. If it doesnt' sell he'll probably relist it so click
anyhow.
http://www.ebay.com/itm/Micronta-Microwave-Leakage-Detector-/290963447557

and a new one for only 15 including shipping
http://www.ebay.com/itm/General-MLD100-Microwave-Leak-Detectors-/200952444879

Here's one for more, $35 http://www.lessemf.com/mw-oven.html

And http://www.ebay.com/bhp/microwave-leak-detector

It makes noise, the lights light up fine, the controls all work,
and it beeps when done, etc. - but it just won't heat up anything.

Did I test the diode properly?

I'm self-taught for the most part, but I would have just measured the
resistance directly with an ohmmeter, using the meter's internal
battery, in both directions. If one direction is many times higher
than the other, it's good. Even if I did it your way, I would do
it my way too, to see if the results confirmed each other.

For more info, ask on sci.electronics.repair


***I used to have an Amana Radarrange model 2. I never saw a model
1, but this one looked just like the image of a microwave everyone
used for years (except compeititors).

I got it used, fixed the door spring and had it for about 10 years.
When it stopped working I called Amana and asked, figuring she might
know which part failed most frequently. She suspected the
magnetron. The next time I called, someone suspected the diode. I
opened the high voltage cage**** and saw that there were cracks on the
wires to the diode (one 20 or 30 times bigger than yours, counting
heat radiation fins). I used silicione sealant by GE (available in
black at auto parts stores, if color matters to the repairer) and put
on large blobs of it, thicker than the thick wires. And it worked for
another 10 years.

****The woman at Amana was very much afraid I wouldn't put the woven
metal gasket back the way it had been and that it would leak. She
also wouldn't send me a schematic. I had to promise her up and down
that I had 20 years experience with electronics, and I would put the
gasket just where it was, and she finally sent me a schematic, for
free. I had to take apart another one^^ and I think they are
designed differently now, but I would be very careful reassembling so
as to not leak microwaves.

The next time it failed it did nothing, so it was the transformer. I
think Amana wanted 380 dollars I said, "That's the price from 1970.
They are worth less now (since you can buy a whole microwave for under
100.) After writing a letter -- I said, Save a few for your museum
and the inventor's grandchildren and sell the rest at a price at which
you will actually sell them -- and being referred to a place near
Harrisburg, they lowered the price to the wholesale price, 250 or so.
Much as I hated to part with model 2, I scrapped it.


^^This latest one has a bad relay, and I'll probably never get around
to fixining it.

 

[Danny D.]

On Mon, 26 Aug 2013 03:30:38 -0700, William Sommerwerck wrote:

> What do you mean by a "microwave diode"?

I meant the high-voltage diode in the microwave oven.

 

[Danny D.]

On Mon, 26 Aug 2013 02:19:29 -0400, micky wrote:

Since apparently there is no current in that direction, how about
taking out the resistor and seeing what it says then?

The resistor is to prevent the diode from burning
up with too much current, I believe.

If I take out the resistor, I probably blow up the diode.

That does not sound like good advice, so I didn't read the
rest of the suggestions for fear of being led astray.

 

[William Sommerwerck]

What do you mean by a "microwave diode"?

To me, it's a point-contact diode used in microwave measurements. My
experience has been that sample-to-sample variation is high.

 

[The Daring Dufas]

On 8/26/2013 5:30 AM, William Sommerwerck wrote:

What do you mean by a "microwave diode"?

To me, it's a point-contact diode used in microwave measurements. My
experience has been that sample-to-sample variation is high.

"microwave diode" can mean many things to me since I've experience in
electronics. The context in which it's being used in this thread is a
discussion of the high voltage diode used in the power supply for the
magnetron in a homeowner's microwave oven. ^_^

TDD

 

[Cydrome Leader]

In sci.electronics.repair Danny D. <dannyd@is.invalid> wrote:

I just tested my microwave diode where, unfortunately, it seems to be good:
http://farm8.staticflickr.com/7358/9594179589_09dac4708b_o.fig

Forward biased with a 9 VDC battery, I measure 7 VDC across the diode;
reverse biased, I read 9 VDC across the diode (given a 200 ohm
current-limiting resistance in series with the battery).

I was hoping the diode was bad, because otherwise, I don't know what's
wrong with the microwave. It does everything but heat up the food.

It makes noise, the lights light up fine, the controls all work,
and it beeps when done, etc. - but it just won't heat up anything.

Did I test the diode properly?

Sort of. A 9 volt battery isn't really a good test for a high voltage
recifier. The forward drop will exceed that of that battery, at least a
rated current of 0.3 to 0.5A, depending on the diode and oven.

The results of your test though, show the diode isn't open and isn't
shorted, so that's good. I'd not bother to replace the diode at this point
of the oven was in front of me.

I'd test the heater coil of the magnetron. It should measure close to dead
short ohms if it's good. If it's open, well, that explains why there's no
heat. You'd also want to make sure the transformer is even being turned
on, you can usually tell this from just listening to the oven or watching
lights flicker when the oven turns on.

Be sure you discarge the cap before you mess around in a microwave oven.

As mentioned in this thread by others, a normal volt meter cannot be
safely used to test the HV section of a microwave. You really don't even
need to for the most part either.

 

[Ralph Mowery]

"micky" <NONONOmisc07@bigfoot.com> wrote in message
news:6tql19hm5cliq6gu13p5imdpsa1i96o98d@4ax.com...

Normally I'd say you should measure the voltages while it's in the
circuit. That's a little different here since you'd have to have the
cover off and that would expose you to a lot of microwaves. OTOH,
it's not working so maybe there are no microwaves. I hate to rely on
ma


I'm self-taught for the most part, but I would have just measured the
resistance directly with an ohmmeter, using the meter's internal
battery, in both directions. If one direction is many times higher
than the other, it's good. Even if I did it your way, I would do
it my way too, to see if the results confirmed each other.

It would be difficult for most people to measure the voltage while the
microwave is running. Not counting on any stray radiation,but at the
voltages in the microwave, it would burn out most meters. Also the high
voltage would most likely go through the insulation and into the person
doing the measuring.
Very few meters that are found are rated for much over 1000 volts, less than
half of what is used in many microwaves.

The ohmmeter in the common meters will not check the diode either. The
voltage drop across the diode in the microwave is more than the meter is set
up to measure in the ohms range. It is not around .7 volts as one would
find in the lower voltage diodes. Internally the diode is made up of
several diodes so the voltage drop is much more.

 

[Arfa Daily]

"Danny D." <dannyd@is.invalid> wrote in message
news:kvfftd$v6h$2@news.albasani.net...

On Mon, 26 Aug 2013 02:19:29 -0400, micky wrote:

Since apparently there is no current in that direction, how about
taking out the resistor and seeing what it says then?

The resistor is to prevent the diode from burning
up with too much current, I believe.

If I take out the resistor, I probably blow up the diode.

That does not sound like good advice, so I didn't read the
rest of the suggestions for fear of being led astray.

It is highly unlikely that any small dry battery would be be able to source
enough current to damage the HV rectifier diode from a microwave oven.
However, the way that you have gone about testing it is perfectly valid, and
the test result you have obtained, indicating a forward conduction with a
voltage drop of 7 volts measured across the diode, and reverse blocking with
9 volts measured across the diode, would suggest that the diode is good. The
reason that you can't normally use a 'standard' ohm meter to measure these
high voltage diodes, is self evident in the large forward voltage drop that
they produce. The internal meter battery often does not source enough
voltage to bias the diode 'on' sufficiently to obtain any meaningful
reading. If the meter has a 'diode test' setting, this most certainly will
not. The reason that these high voltage diodes behave like this, is because
internally, they are many ordinary diodes stacked in series to get the high
PIV rating. Think 10 x 1N4007 in series, which would give you a diode with a
PIV rating of around 10 kV, but with a forward voltage drop of 6 or 7 volts.

I agree with others that the problem is probably the mag. Its heater may
have gone open. That can be measured with the transformer heater winding
disconnected. Other possibilities are a high voltage fuse gone open, if it
has one, or a thermal protection switch that's gone open or failure of the
high voltage transformer control relay, or failure of the circuitry that
drives the relay.

When you start it up, and expect it to be producing microwaves, does the
transformer 'grunt' ? Current limiting for the mag is achieved magnetically
with shunts in the transformer core, and this causes it to produce an easily
audible "I'm struggling" buzz when the mag is working and drawing current.

If you do hear this, the chances are that the high voltage circuitry and the
mag are probably working, and it may be something else. Although rare, I
have on odd occasions seen crap blocking the waveguide into the oven cavity,
although that may no longer be a possibility with modern designs, as I
haven't had occasion to work on any for some time.

Aside from all this, if you are not greatly experienced working on
line-powered electronics with the covers removed, please be VERY CAREFUL !!!
Apart from the possibility of serious shock or death from accidentally
wrapping yourself around the line power circuitry, the high voltage supply
on a microwave oven is also potentially lethal. At the very least, it can
give you a very serious and painful shock, and if the mag is not drawing any
current, the high voltage capacitor can stay charged to a very high voltage
for a very long time after power is removed.

TAKE HEED !!! :-\

Arfa

 

[Stormin Mormon]

Yes, doesn't look fat in that outfit at all.

Did your microwave diode just lose weight?

Love what you've done to your diode's hair.


..
Christopher A. Young
Learn about Jesus
www.lds.org
..

 

[Phil Allison]

"Arfa Daily"

Aside from all this, if you are not greatly experienced working on
line-powered electronics with the covers removed, please be VERY CAREFUL
!!! Apart from the possibility of serious shock or death from accidentally
wrapping yourself around the line power circuitry, the high voltage supply
on a microwave oven is also potentially lethal. At the very least, it can
give you a very serious and painful shock, and if the mag is not drawing
any current, the high voltage capacitor can stay charged to a very high
voltage for a very long time after power is removed.

TAKE HEED !!!

** The OP is just begging for a Darwin Award.

So who are you to spoil his one moment of fame ??

http://en.wikipedia.org/wiki/Darwin_Awards

How amazing to find that the famous Award originates with USENET !!!!!!!



..... Phil

 

[JW]

On Mon, 26 Aug 2013 15:17:35 +0100 "Arfa Daily" <arfa.daily@ntlworld.com>
wrote in Message id: <5sJSt.661$on4.329@fx11.am4>:

The internal meter battery often does not source enough
voltage to bias the diode 'on' sufficiently to obtain any meaningful
reading. If the meter has a 'diode test' setting, this most certainly will
not. The reason that these high voltage diodes behave like this, is because
internally, they are many ordinary diodes stacked in series to get the high
PIV rating. Think 10 x 1N4007 in series, which would give you a diode with a
PIV rating of around 10 kV, but with a forward voltage drop of 6 or 7 volts.

That's true of most DMMs, but there are exceptions. My Keithley 2000 will
bias a diode up to 10VDC. Useful for checking smaller zeners as well.

 

[micky]

On Mon, 26 Aug 2013 04:18:18 +0000 (UTC), "Danny D."
<dannyd@is.invalid> wrote:

I just tested my microwave diode where, unfortunately, it seems to be good:
see other post for picture.

Forward biased with a 9 VDC battery, I measure 7 VDC across the diode;

reverse biased, I read 9 VDC across the diode (given a 200 ohm
current-limiting resistance in series with the battery).

Since apparently there is no current in that direction, how about
taking out the resistor and seeing what it says then?

I was hoping the diode was bad***, because otherwise, I don't know what's
wrong with the microwave. It does everything but heat up the food.

Normally I'd say you should measure the voltages while it's in the
circuit. That's a little different here since you'd have to have the
cover off and that would expose you to a lot of microwaves. OTOH,
it's not working so maybe there are no microwaves. I hate to rely on
maybe. Do you have a microwave detector. I got one at Radio Shack
about 30 years ago and it works well. I was able to test it because
at that time I had Amana Model 2, and it didn't have door latches on
it. So I could open the door a little before the safety switches
turned the machine off, and I could see the detector reading rise from
zero to at least half way across the scale (but I only allowed that
for a second.) After that, I could check door leakage. RS doesn't
still sell them iirc but you might find one used, or you might find a
new one sold through another channel.

Here's exactly the same one I have, no bids yet, 18 hours left from my
post time. If it doesnt' sell he'll probably relist it so click
anyhow.
http://www.ebay.com/itm/Micronta-Microwave-Leakage-Detector-/290963447557

and a new one for only 15 including shipping
http://www.ebay.com/itm/General-MLD100-Microwave-Leak-Detectors-/200952444879

Here's one for more, $35 http://www.lessemf.com/mw-oven.html

And http://www.ebay.com/bhp/microwave-leak-detector

It makes noise, the lights light up fine, the controls all work,
and it beeps when done, etc. - but it just won't heat up anything.

Did I test the diode properly?

I'm self-taught for the most part, but I would have just measured the
resistance directly with an ohmmeter, using the meter's internal
battery, in both directions. If one direction is many times higher
than the other, it's good. Even if I did it your way, I would do
it my way too, to see if the results confirmed each other.

For more info, ask on sci.electronics.repair


***I used to have an Amana Radarrange model 2. I never saw a model
1, but this one looked just like the image of a microwave everyone
used for years (except compeititors).

I got it used, fixed the door spring and had it for about 10 years.
When it stopped working I called Amana and asked, figuring she might
know which part failed most frequently. She suspected the
magnetron. The next time I called, someone suspected the diode. I
opened the high voltage cage**** and saw that there were cracks on the
wires to the diode (one 20 or 30 times bigger than yours, counting
heat radiation fins). I used silicione sealant by GE (available in
black at auto parts stores, if color matters to the repairer) and put
on large blobs of it, thicker than the thick wires. And it worked for
another 10 years.

****The woman at Amana was very much afraid I wouldn't put the woven
metal gasket back the way it had been and that it would leak. She
also wouldn't send me a schematic. I had to promise her up and down
that I had 20 years experience with electronics, and I would put the
gasket just where it was, and she finally sent me a schematic, for
free. I had to take apart another one^^ and I think they are
designed differently now, but I would be very careful reassembling so
as to not leak microwaves.

The next time it failed it did nothing, so it was the transformer. I
think Amana wanted 380 dollars I said, "That's the price from 1970.
They are worth less now (since you can buy a whole microwave for under
100.) After writing a letter -- I said, Save a few for your museum
and the inventor's grandchildren and sell the rest at a price at which
you will actually sell them -- and being referred to a place near
Harrisburg, they lowered the price to the wholesale price, 250 or so.
Much as I hated to part with model 2, I scrapped it.


^^This latest one has a bad relay, and I'll probably never get around
to fixining it.

 

[micky]

On Mon, 26 Aug 2013 11:58:37 +0000 (UTC), "Danny D."
<dannyd@is.invalid> wrote:

On Mon, 26 Aug 2013 02:19:29 -0400, micky wrote:

Since apparently there is no current in that direction, how about
taking out the resistor and seeing what it says then?

The resistor is to prevent the diode from burning
up with too much current, I believe.

I think so too.

>If I take out the resistor, I probably blow up the diode.

Now why would you think that? Did you fail to notice that if there
is 9 volts across the diode, there is no current running through the
diode. How can you imagine that removing a 200 ohm resistorr will
increase the current much? And with a 9-volt battery no less.

That does not sound like good advice, so I didn't read the
rest of the suggestions for fear of being led astray.

Since ;your answer does not sound like you think well, I won't read
the rest of your posts, for fear I'll read foolishness but be too weak
to avoid believing it. .

 

[Danny D.]

On Mon, 26 Aug 2013 15:17:35 +0100, Arfa Daily wrote:

the test result you have obtained, indicating a forward conduction with a
voltage drop of 7 volts measured across the diode, and reverse blocking with
9 volts measured across the diode, would suggest that the diode is good.

Thanks for that confirmation. Bummer. But now at least I know it's
most likely the magnetron.

 

[Danny D.]

On Mon, 26 Aug 2013 15:28:18 -0400, micky wrote:

Did you fail to notice that if there
is 9 volts across the diode, there is no current running through the
diode.

Except there isn't 9 volts across the diode.
There was 7 volts across the diode.

 

[Arfa Daily]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b817h8F95g0U1@mid.individual.net...

"Arfa Daily"

Aside from all this, if you are not greatly experienced working on
line-powered electronics with the covers removed, please be VERY CAREFUL
!!! Apart from the possibility of serious shock or death from
accidentally wrapping yourself around the line power circuitry, the high
voltage supply on a microwave oven is also potentially lethal. At the
very least, it can give you a very serious and painful shock, and if the
mag is not drawing any current, the high voltage capacitor can stay
charged to a very high voltage for a very long time after power is
removed.

TAKE HEED !!!


** The OP is just begging for a Darwin Award.

So who are you to spoil his one moment of fame ??

http://en.wikipedia.org/wiki/Darwin_Awards

How amazing to find that the famous Award originates with USENET !!!!!!!



.... Phil

LOL !! Nice one, Phil

Arfa

 

[micky]

On Tue, 27 Aug 2013 00:46:55 +0000 (UTC), "Danny D."
<dannyd@is.invalid> wrote:

On Mon, 26 Aug 2013 15:28:18 -0400, micky wrote:

Did you fail to notice that if there
is 9 volts across the diode, there is no current running through the
diode.

Except there isn't 9 volts across the diode.
There was 7 volts across the diode.

That was forward biased. My reply was clearly about reverse biased.
If you hadn't snipped so much and didn't want so much for me to be
wrong, you'd have noticed.

Quote

Forward biased with a 9 VDC battery, I measure 7 VDC across the diode;

reverse biased, I read 9 VDC across the diode (given a 200 ohm
current-limiting resistance in series with the battery).

Since apparently there is no current in that direction, how about
taking out the resistor and seeing what it says then?

End Quote.

I added the blank line between your first and second line so there'd
be no doubt which direction I was talking about.