Samsung MW8490W, about 6.5 years old. Tried microwaving something
today, and the microwave just vibrates and buzzes. It's definately a
60Hz-based buzz. No arcing or odd smells. Everything appears OK
except the metal enclosure vibrates violently like there's a loose
transformer in there.
Oh, it won't heat water, and is drawing only about 350W from the outlet
when running (rear label says 1.5KW).

I can tell you everything you want to know about electronics (well,
almost), but microwaves are somewhat of a mystery to me.

Any ideas on what's wrong, or where to start?

writes:

Samsung MW8490W, about 6.5 years old. Tried microwaving something
today, and the microwave just vibrates and buzzes. It's definately a
60Hz-based buzz. No arcing or odd smells. Everything appears OK
except the metal enclosure vibrates violently like there's a loose
transformer in there.
Oh, it won't heat water, and is drawing only about 350W from the outlet
when running (rear label says 1.5KW).

I can tell you everything you want to know about electronics (well,
almost), but microwaves are somewhat of a mystery to me.

Any ideas on what's wrong, or where to start?

Shorted high voltage diode or magnetron.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Stay out of that thing. And if you could buy a new magnetron, it would
probably cost more than a new microwave.

Perce


On 02/26/06 06:48 pm wrote:

Samsung MW8490W, about 6.5 years old. Tried microwaving something
today, and the microwave just vibrates and buzzes. It's definately a
60Hz-based buzz. No arcing or odd smells. Everything appears OK
except the metal enclosure vibrates violently like there's a loose
transformer in there.
Oh, it won't heat water, and is drawing only about 350W from the outlet
when running (rear label says 1.5KW).

I can tell you everything you want to know about electronics (well,
almost), but microwaves are somewhat of a mystery to me.

Any ideas on what's wrong, or where to start?

Stay out, why? I know there's a HV capacitor in there, and I know
electronics plenty good enough to know what not to do.

And yes, you're right. Magnetrons are expensive. However, I just
tracked it down to the diode. 0.040 V drop in both directions. Yeah,
it's shorted. Much cheaper than a new microwave.

Percival P. Cassidy wrote:
Stay out of that thing. And if you could buy a new magnetron, it would
probably cost more than a new microwave.

Perce


On 02/26/06 06:48 pm wrote:

Samsung MW8490W, about 6.5 years old. Tried microwaving something
today, and the microwave just vibrates and buzzes. It's definately a
60Hz-based buzz. No arcing or odd smells. Everything appears OK
except the metal enclosure vibrates violently like there's a loose
transformer in there.
Oh, it won't heat water, and is drawing only about 350W from the outlet
when running (rear label says 1.5KW).

I can tell you everything you want to know about electronics (well,
almost), but microwaves are somewhat of a mystery to me.

Any ideas on what's wrong, or where to start?

mm wrote:
On 26 Feb 2006 16:35:21 -0800, wrote:


Sam Goldwasser wrote:
writes:

Samsung MW8490W, about 6.5 years old. Tried microwaving something
today, and the microwave just vibrates and buzzes. It's definately a
60Hz-based buzz. No arcing or odd smells. Everything appears OK
except the metal enclosure vibrates violently like there's a loose
transformer in there.
Oh, it won't heat water, and is drawing only about 350W from the outlet
when running (rear label says 1.5KW).

I can tell you everything you want to know about electronics (well,
almost), but microwaves are somewhat of a mystery to me.

Any ideas on what's wrong, or where to start?

Shorted high voltage diode or magnetron.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Any quick checks that can be made? Should the two terminals to the mag
have some low resistance? (I'm not sure what they connect to)

I'm also going to read up some more on how these things work.

The most important thing is to either not mess with the cage around
the microwave part, or to put it back EXACTLY the way you find it. At
first the Amana girl refused to send me a schematic (back when I
didn't realize how simple they are) because she thought I'd radiate
myself or my eyes to death. Apparently the metal side of the oven,
where the electronics are, is not enough to keep the waves inside.

You might want to get a microwave tester (10 dollars at Radio Shack)
to make sure there is no leakage. I calibrated mine by pulling the
door open a little but less than it took to have the oven turn off.
now that the ovens latch instead of just close, this might be harder
to do. The RS tester was calibrated fine to begin with afaict.

There's no cage around the microwave parts. It's in the open once the
outside shell has been removed. Nothing that I'm messing with here
looks real critical....just high voltage stuff. I'm not remove the mag
or anything.

writes:

mm wrote:
On 26 Feb 2006 16:35:21 -0800, wrote:


Sam Goldwasser wrote:
writes:

Samsung MW8490W, about 6.5 years old. Tried microwaving something
today, and the microwave just vibrates and buzzes. It's definately a
60Hz-based buzz. No arcing or odd smells. Everything appears OK
except the metal enclosure vibrates violently like there's a loose
transformer in there.
Oh, it won't heat water, and is drawing only about 350W from the outlet
when running (rear label says 1.5KW).

I can tell you everything you want to know about electronics (well,
almost), but microwaves are somewhat of a mystery to me.

Any ideas on what's wrong, or where to start?

Shorted high voltage diode or magnetron.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Any quick checks that can be made? Should the two terminals to the mag
have some low resistance? (I'm not sure what they connect to)

I'm also going to read up some more on how these things work.

The most important thing is to either not mess with the cage around
the microwave part, or to put it back EXACTLY the way you find it. At
first the Amana girl refused to send me a schematic (back when I
didn't realize how simple they are) because she thought I'd radiate
myself or my eyes to death. Apparently the metal side of the oven,
where the electronics are, is not enough to keep the waves inside.

You might want to get a microwave tester (10 dollars at Radio Shack)
to make sure there is no leakage. I calibrated mine by pulling the
door open a little but less than it took to have the oven turn off.
now that the ovens latch instead of just close, this might be harder
to do. The RS tester was calibrated fine to begin with afaict.

There's no cage around the microwave parts. It's in the open once the
outside shell has been removed. Nothing that I'm messing with here
looks real critical....just high voltage stuff. I'm not remove the mag
or anything.

Right. Just try not to electrocute yourself in the process. If you don't
remove the magnetron, there is no critical seal you'll be affecting.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

mm writes:

On 27 Feb 2006 04:02:36 -0800, wrote:


The most important thing is to either not mess with the cage around
the microwave part, or to put it back EXACTLY the way you find it. At
first the Amana girl refused to send me a schematic (back when I
didn't realize how simple they are) because she thought I'd radiate
myself or my eyes to death. Apparently the metal side of the oven,
where the electronics are, is not enough to keep the waves inside.

You might want to get a microwave tester (10 dollars at Radio Shack)
to make sure there is no leakage. I calibrated mine by pulling the
door open a little but less than it took to have the oven turn off.
now that the ovens latch instead of just close, this might be harder
to do. The RS tester was calibrated fine to begin with afaict.

There's no cage around the microwave parts. It's in the open once the
outside shell has been removed. Nothing that I'm messing with here
looks real critical....just high voltage stuff. I'm not remove the mag
or anything.

Interesting. I tguess this is part of how they lowered the weight
of these things, like they lowered the weight of tv's in part by
removing the cage around the high voltage parts. Of course if you
don't touch the tv hv, there is no problem at all, but microwaves go
zooming around the room. Maybe it was never the danger they thought
it was, or they figured out how not to generate excess microwaves
without and thus didn't need a cage.

I've never seen a cage around the magnetron in a microwave oven. It's
all metal that's exposed outside the waveguide except for the filament
feedthroughs. As long as holes are a small fraction of the wavelength,
very little microwave energy will get through. And, the metal cover over
the entire oven adds another layer of protection.

TVs in the old days had high voltage rectifier tubes and flybacks with
exposed terminals. Modern CRT-based equipment has the flyback entirely
potted so there is no exposed HV.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

"Sam Goldwasser" wrote in message
...
mm writes:

On 27 Feb 2006 04:02:36 -0800, wrote:


The most important thing is to either not mess with the cage around
the microwave part, or to put it back EXACTLY the way you find it. At
first the Amana girl refused to send me a schematic (back when I
didn't realize how simple they are) because she thought I'd radiate
myself or my eyes to death. Apparently the metal side of the oven,
where the electronics are, is not enough to keep the waves inside.

You might want to get a microwave tester (10 dollars at Radio Shack)
to make sure there is no leakage. I calibrated mine by pulling the
door open a little but less than it took to have the oven turn off.
now that the ovens latch instead of just close, this might be harder
to do. The RS tester was calibrated fine to begin with afaict.

There's no cage around the microwave parts. It's in the open once the
outside shell has been removed. Nothing that I'm messing with here
looks real critical....just high voltage stuff. I'm not remove the mag
or anything.

Interesting. I tguess this is part of how they lowered the weight
of these things, like they lowered the weight of tv's in part by
removing the cage around the high voltage parts. Of course if you
don't touch the tv hv, there is no problem at all, but microwaves go
zooming around the room. Maybe it was never the danger they thought
it was, or they figured out how not to generate excess microwaves
without and thus didn't need a cage.

I've never seen a cage around the magnetron in a microwave oven. It's
all metal that's exposed outside the waveguide except for the filament
feedthroughs. As long as holes are a small fraction of the wavelength,
very little microwave energy will get through. And, the metal cover over
the entire oven adds another layer of protection.

TVs in the old days had high voltage rectifier tubes and flybacks with
exposed terminals. Modern CRT-based equipment has the flyback entirely
potted so there is no exposed HV.


Usually when the magnatron goes out, the unit appears to run normally but
the food don't get hot. If there is a short such that the HV circuits are
making a lot of noise, then the unit is probably trash (for ex. the HV
transformer is shot or there are multiple component failures). At the very
least, you need basic troubleshooting knowledge of the circuit. Unless you
are working on an expensive built in or over the range model, I would just
replace it. As you probably know, small ovens cost way less than $100.

The OP described a loud buzzing which could be a stuck motor. There are
several in an oven. Notably the exhaust fan and the one that turns the
blades that "mix" the microwaves around the oven cavity. A frozen motor
will,often make a lot of noise. These moving parts have lower reliability
than the HV circuits

You may be able to operate the oven with the magnatron disconnected. In
this manner, you can confirm the other functions (timer relay, fans,
interlocks, no corona around HV circuits etc). Without an HV probe, you can
often tell if HV is present by holding a fluorescent tube near (but not
touching) the circuit while you ground the other end with your hand, it will
light at the end near the HV. You will not know if it is the correct
voltage.

wrote in message
oups.com...
Stay out, why? I know there's a HV capacitor in there, and I know
electronics plenty good enough to know what not to do.

And yes, you're right. Magnetrons are expensive. However, I just
tracked it down to the diode. 0.040 V drop in both directions. Yeah,
it's shorted. Much cheaper than a new microwave.


Hope that's all it is. In my experiance, HV failures tend to cascade to
several components.

"PipeDown" writes:

wrote in message
oups.com...
Stay out, why? I know there's a HV capacitor in there, and I know
electronics plenty good enough to know what not to do.

And yes, you're right. Magnetrons are expensive. However, I just
tracked it down to the diode. 0.040 V drop in both directions. Yeah,
it's shorted. Much cheaper than a new microwave.


Hope that's all it is. In my experiance, HV failures tend to cascade to
several components.

There aren't that many HV components: HV diode, HV cap, magnetron.

So, conceivably, a bad magnetron took out the diode (though the exact
mechanism isn't clear). The cap is still good or else the main fuse would
have blown. If it was the HV transformer, that wouldn't damage the HV diode.
So, you're left with the HV diode.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Buzzing is the last thing a microwave does before detonates.

HTH

Steve

mm writes:

On Mon, 27 Feb 2006 15:30:07 -0800, "Steve B"
wrote:

Buzzing is the last thing a microwave does before detonates.

HTH

Don't they have a red light timer inside that counts down to zero?
All the bombs on tv have that.

And unmarked red and blue wires.....

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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