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Posted by mynick on October 15, 2009, 12:02 pm
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?
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Posted by mm on October 15, 2009, 1:19 pm
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.
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Posted by jamesgangnc on October 15, 2009, 2:06 pm
> 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,
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Posted by Zootal on October 15, 2009, 2:07 pm
> 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.
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Posted by JIMMIE on October 15, 2009, 2:38 pm
> 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
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>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?