no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

On Thu, 15 Oct 2009 09:02:27 -0700 (PDT), mynick
wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

This is tube that came with a microwave oven, and the tranformer that
came with it too?

Did it used to work?

I think it unlikely that it requires a mere 1 volt more voltage, or
that the working transformer doesn't provide the right voltage. The
transformer may be the most expensive part ot replace.

Be careful running the thing with the cover off. I presume there is
still a shield around the microwave tube, but if so, absolutely don't
run the thing without the shield. Radio Shack used to sell
inexpensive (10$) microwave detectors, for testing leakage around
microwave ovens. Maybe they still sell them. I know that mine
worked well, because I had an overn without a latch, and by pulling
the door open a little, I was able to watch the meter reading rise
from very very low to quite a bit higher.

On Oct 15, 12:02*pm, mynick wrote:
no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Loud hum sometimes means something is shorted. The increased load on
the transformer makes it hum more. You can't always detect a short in
a high voltage component with an ohm meter. You can measure the
heating element voltage with an multi-meter but you really ned to be
careful. There is probably a diode and capacitor in the high voltage
circuit as well. If the diode has shorted the ac load will go through
the capacitor and that can also cause the high hum. I tried to fix
one once that had a bad magnitron but the magnitron was about half the
cost of a whole new microwave,

"mynick" wrote in message
...
no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Do you have experience with high voltage and RF equipment, especially
microwave/radar frequencies? Do you have the equipment for measuring high
voltage safely? You need something that can handle 10,000 volts - a cheap
Radio Shack meter will not do this safely. By the questions you ask, I'm
guessing you don't.

I very strongly recommend that you close up the cabinet and either take it
to someone that knows what they are doing, or throw it in the trash.
Microwave ovens are incredibly dangerous if you don't know what you are
doing, and you can end up seriously injured or dead real fast. It's not
worth it - just throw it in the trash.

If you really want to try to fix it and risk killing yourself and burning
down your house, etc. :-)

Try here; http://www.gallawa.com/microtech/

It has some basic service procedures, but I don't think you will find
anything telling you how to troubleshoot the RF or high voltage circuitry.
That requires special knowledge and equipment that not even a lot of the
techs that fix these things have.

On Oct 15, 12:02*pm, mynick wrote:
no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Could be a lot of things most are unsafe to test without proper
equipment and experience. The voltages exceed that which can be safely
handled by most voltmeters. Back when I used to work on these things
the first things I would check is the diode, filament caps, power
supply cap. I could do this safely with ohm meter and Hi-pot tester.
I had a homebrew test bed for checking transformers, don't even think
of measuring voltage on these even the filament are at multi kilovolt
levels and grounded to the chassis. The decision to replace the maggie
was usually based on a process of elimination.

Jimmie

abo mahab wrote:
Belief in God by Shaikh Shahidullah Faridi


It is mistakenly imagined by some that belief in a Supreme Being as
the Creator and Controller of the universe is a mere emotional
aspiration, a superstition of ancient times, irrational and illogical,
and exploded by modern science....

I see you're posting from 93.98.28.228, which works out to be

IP address: 93.98.28.228
Reverse DNS: [No reverse DNS entry per ns-pri.ripe.net.]
Reverse DNS authenticity: [Unknown]
ASN: 34397
ASN Name: CYBERIA-RUH (Cyberia Riyadh Autonomous
System)
IP range connectivity: 2
Registrar (per ASN): RIPE
Country (per IP registrar): SA [Saudi Arabia]
Country Currency: SAR [Saudi Arabia Riyals]
Country IP Range: 93.98.0.0 to 93.98.255.255
Country fraud profile: Normal
City (per outside source): Riyadh, Ar Riyad
Country (per outside source): SA [Saudi Arabia]
Private (internal) IP? No
IP address registrar: whois.arin.net

Whatsa matter? Couldn't find anyone in your country interested in listening
to you?

In article , JIMMIE wrote:
On Oct 15, 12:02=A0pm, mynick wrote:
no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Could be a lot of things most are unsafe to test without proper
equipment and experience. The voltages exceed that which can be safely
handled by most voltmeters. Back when I used to work on these things
the first things I would check is the diode, filament caps, power
supply cap. I could do this safely with ohm meter and Hi-pot tester.
I had a homebrew test bed for checking transformers, don't even think
of measuring voltage on these even the filament are at multi kilovolt
levels and grounded to the chassis. The decision to replace the maggie
was usually based on a process of elimination.

I ran into that recently. It sort of started to work by generating heat,
but that didn't last long. I like using an old analog meter with the 5 KV scales.
I didn't get a chance to replace the manetron. It cost the owner a bunch for the transformer
and diode.

The diode and transformer became BAD, but don't know at what point.
Before or after the manetron went bad.

greg

mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?


Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.

mynick wrote:
no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?
Hi,
More than magnetron. Suspect your HV source.

mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?
Sounds like it maybe the HV-Diode..

P.S.
You most likely won't be able to test it with your
DMM unless it's totally shorted.

In article
communications,
jeff_wisnia wrote:

mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?


Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.

Jeff

Or as a guy I know would so eloquently warn... "Dont ya'll be messin
with that s**t lest you know what you doin; it'll up'n give yo ass a
dirt nap"

Good advise too. I hate 'dirt naps' anymore, especially now that I'm a
bit older.

Microwaves reached disposable appliance status eons ago... if it's not
in warranty, spring for a new one, they're cheap.

Erik

On Oct 16, 4:01 am, Erik wrote:
In article
communications,

jeff_wisnia wrote:
mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.

Jeff

Or as a guy I know would so eloquently warn... "Dont ya'll be messin
with that s**t lest you know what you doin; it'll up'n give yo ass a
dirt nap"

Good advise too. I hate 'dirt naps' anymore, especially now that I'm a
bit older.

Microwaves reached disposable appliance status eons ago... if it's not
in warranty, spring for a new one, they're cheap.

Erik

I meant what is going to happen if you try replace original magnetron
with one that has 4.13v or 3.6v filament voltage but original hv
transformer gives 3.15V

On Oct 16, 8:07*am, mynick wrote:
On Oct 16, 4:01 am, Erik wrote:



In article
communications,

*jeff_wisnia wrote:
mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.

Jeff

Or as a guy I know would so eloquently warn... "Dont ya'll be messin
with that s**t lest you know what you doin; it'll up'n give yo ass a
dirt nap"

Good advise too. I hate 'dirt naps' anymore, especially now that I'm a
bit older.

Microwaves reached disposable appliance status eons ago... if it's not
in warranty, spring for a new one, they're cheap.

Erik

I meant what is going to happen if you try replace original magnetron
with one that has 4.13v or 3.6v filament voltage but original hv
transformer gives 3.15V

Video Please, I want to see this on stupid microwave tricks.

Jimmie

On Oct 16, 10:07*am, mynick wrote:
On Oct 16, 4:01 am, Erik wrote:





In article
communications,

*jeff_wisnia wrote:
mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.

Jeff

Or as a guy I know would so eloquently warn... "Dont ya'll be messin
with that s**t lest you know what you doin; it'll up'n give yo ass a
dirt nap"

Good advise too. I hate 'dirt naps' anymore, especially now that I'm a
bit older.

Microwaves reached disposable appliance status eons ago... if it's not
in warranty, spring for a new one, they're cheap.

Erik

I meant what is going to happen if you try replace original magnetron
with one that has 4.13v or 3.6v filament voltage but original hv
transformer gives 3.15V- Hide quoted text -

- Show quoted text -

Those numbers don't seem to make any sense at all. Sounds like maybe
something is shorted or the capacitor or rectifier is shot.

BE VERY, VERY CAREFUL. LETHAL VOLTAGES!!!!!!!.

My advice is always, don't mess with it unless you are a competent
high voltage/radio transmitter technician!
There are voltages of 5000+ volts and potential RF radiation that can
fry your eyes (cos that's what it does in minutes to meat, eh?). In
effect a m.wave oven is a one kilowatt radio transmitter in a tin box!
And much less than that can easily kill you!!!!!!!!

The circuit is complex enough that the typical do it yourself-er may
not be able to follow. For example we recently fixed, in less than 20
minutes, a microwave that the owner, a capable sort of chap for most
'carpentry type' repairs, but not an electronics technician, thought
had a bad component in the power supply (HV transformer, rectifier,
capacitor etc.) .

Then he thought it was something to do with the control panel!

Initially I had thought it might be the contacts of the relay on the
control panel that switches most of the power the m.wave uses. One
could hear it closing but no power!

It wasn't any of those! The problem was a defective door micro-switch
(Canadian Spec. not necessarily same as USA by the way!) that
prevented basic 115 volts AC from reaching the fan, the power supply,
the interior light etc. etc. A somewhat basic fault as it turned out.
We had a spare micro-switch of the same spec. from a junked m.wave
fairly easy install, stand back, since the cover was still off, for a
test and it was all done.

Not only the wrong diagnosis, twice, plus my first thought about the
control realy; but the owner had put the cover back on incorrectly and
it had a slight gap where microwaves 'might' be able to leak right
near the door 'handle'! Not good.

For goodness sake 'BE CAREFUL' a replacement m.wave can be had for
around $50 and the risk is not worth it.

In article communications, jeff_wisnia wrote:
mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?


Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.


I was checking out an amplifier I built and broke, and sitting for a couple years.
Sure enough, I got a spark messing around with it.

greg

On Oct 16, 6:14*am, (GregS) wrote:
In article communications, jeff_wisnia wrote:

mynick wrote:

no shorts betweenmagnetroncontacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is itdead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?

Watch out for a big capacitor in there which in some cases can give you
a nasty high voltage bite even after the oven has been unplugged for a
while.

I was checking out an amplifier I built and broke, and sitting for a couple years.
Sure enough, I got a spark messing around with it.

greg

If the filament voltage-current is too low maybe it will not
emmit,why else is that magnetron spec?