If you are only on the filiment of the megatron and not in the circuit it is
probably ok. If the megatron is still connected, you may be meauring the
filiment windings of the transformer.
Some high voltage diodes are made of several lower voltage units in series
in the same case. The diode function of the Fluke may not have enough
voltage to check this out and will show open. Here is one way to check to
see if it is actually open.
They use a 9 volt battery and the voltage scale of the meter, One way will
show open and the other will show a few volts less than 9 if the diode is
On Tue, 18 Dec 2012 00:35:25 -0500, Ralph Mowery wrote:
That's a nice procedure which I will try in the morning.
Thanks for pointing it out - as I would have thought the
basic diode function of the Fluke 75 would have sufficed.
At the moment, it shows the diode as bad - but - as you
noted - that may be an anomaly due to the voltage of the Fluke
in diode mode.
On Monday, December 17, 2012 10:02:16 PM UTC-7, Danny D. wrote:
The electronics great RepairFAQ.org has information about microwave
oven repair: http://www.repairfaq.org/sam/micfaq.htm
Those high voltage diodes will read open with a digital meter because
they're made of several diodes in series to handle the thousands
of volts, and usually digital meter won't apply enough voltage to
make all those diodes conduct. So either try an old-style analog
meter set to a higher ohms scale (x100, x1000, x10,000), or
apply at least 6V - 9V DC through a 1,000 ohm resistor and measure
directly across the diode. If the diode is open, you'll see the
source voltage, but if it conducts, the voltage will be lower.
The big high voltage capacitor has to be discharged before handling
it. It almost always contains a bleeder resistor to do that, but
bleeders fail in use, so assume it's not there. Get a screwdriver
with a plastic handle on it (it's not enough to wrap electrical tape
around a metal handle; the voltage is way too high), and wrap several
turns of BARE solid copper wire around it. Connect the other end of
that wire to a 10,000 ohm, 10 watt resistor, and connected the other
resistor lead securely to bare metal of the oven's chassis. Touch
the tip of the screwdriver to each lead of the capacitor for 30
seconds. Finally, touch the screwdriver shaft to both leads of the
Prices for microwaves oven parts vary greatly, and sometimes
electronics parts dealers are cheaper than appliance dealers. Some
of the former include MCM Electronics, Dalbani, Premium Parts, and
You don't need an exact replacement magnatron, just somethign
compatible mechanically and electrically, and for our Sharp
onvection/microwave ovens I've used L-G magnatrons. Also any
replacement high voltage capacitor should have the same microfarad
(uF) rating as the original because using one with a different
capacitance rating changing it changes the power output roughly
proportionally, meaing the programmed cooking modes may not work
right because they're not calibrated for a higher or lower power.
The magnatron is usually held in place with 3-4 bolts or nuts, and
you absolutely want them to be secured so the magnatron is completely
flush with the mounting surface. Otherwise microwavess will leak past
the brass braided ring seal.
The magnatron has to be cooled with a fan, so be sure that fan works
by feeling for air through the rear vent. There's probably a bimetal
thermostat mounted on the magnatron to shut it off if it gets too
hot, and you may want to replace it because I had one that got stuck
in the on position. They're made with several different temperature
I wouldn't turn on a microwave without the cover completely reattached,
including with all its screws, to prevent electrical shock and also
injury in case the capacitor explodes.
First you have to determine that it's bad. Then why it failed to
make sure the new one doesn't fail too.
Then you have to find the exact magnetron...at an affordable price.
If you know what you're doing, you might be able to find an equivalent
magnetron...whatever that means...or cobble in a different magnetron.
That's just not practical for most of us.
The only person who can answer that question is the one with the tape
and the candidate oven.
The standard answer is, microwaves are cheap, go buy a new one.
If you must fit the same hole, your quest is complicated to the extent that
most people won't be able to offer any useful advice.
Call up someone who refurbishes kitchens and ask them.
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