Maytag microwave hums and then internal fuse blows. I replaced the blown fuse and started heating cycle, microwave hummed again and the fuse is again blown.

You would better served replacing unit. Throwing parts at it is an unnecessary step.

did you check and replace the door switches

On many newer microwaves the control panel can stay lit even if the fuse
is blown. (Cartridge fuse inside microwave). If the microwave panel is functional but
no humming this would be a good indication of that.

Make sure power is off before replacing the fuse. Be aware the capacitors may still hold
a good charge and avoid touching the leads to them. (They look like metal cans with tabs
usually). The fuse will be an automotive style fuse with a ceramic middle. These are
available for a couple of dollars at any appliance parts store, and possibly radio shack.
The rating is stamped on the metal ends (250 V= two hundred fifty volts) (4A= four amps)
Make sure to use exact amperage and equal or higher voltage rating. These are a slow blow
fuse.

If the microwave is humming but not cooking then I would suspect the Magnetron tube
has failed. Many times the cost of the replacement doesn't justify it's purchase.
Hope this helps.

A microwave not heating up is caused by one or more of the following -

1) Failed controller board (unlikely if you are getting a clock readout and you can get the various functions to work, just no heat)
2) Failed door switch
3) Failed thermal fuse, when used
4) Blown power fuse that is dedicated to the microwave circuit
5) Bad diode
6) Bad capacitor
7) Bad magnetron
8) Bad transformer

Door switches insure the microwave circuit will not engage when the door is open. Slamming the door of the microwave is hard on the switch.

The thermal due is wired into the microwave harness, and is a melting allow type, based on heat buildup within the oven. Always replace with a fuse of the same thermal rating.

The power fuse is a special type and should only be replaced with that same type and rating. It is easily tested.

The diode is a relatively inexpensive part, and is not easily tested. If a grumble is heard coming from electrical area of the unit, then the diode could be shorted.

A shorted capacitor will blow the fuse immediately. And open capacitor will cause a "no heat" condition.

A bad magnetron will also cause a low level hum or grumble from the transformer. But is may also cause no other identifiable symptom of failure.

A bad transformer will exhibit a grumble or hum, and may or may not blow the fuse. But be careful here, the secondary of the transformer produces very high voltages, up to 2.5Kv. Few people own a meter capable of measuring such voltages.

Service and repair of microwave ovens is dangerous work. If you don't know what your doing, DO NOT ATTEMPT TO SERVICE A UNIT WITHOUT INSTRUCTION

That loud hum is an indication that the Magnetron is shorted.

Okay, first we need to separate the situations. You were boiling water on the stove and had the range hood fan running to **** up the steam. Then you put something in the microwave to heat and you heard a pop and then zip-o.

The water on the stove has nothing to do with the situation, the fan you turn on is not part of the microwave, so it has nothing to do with the microwave.

The pop you heard and then the humming suggests the magnetron failed. You said you found a blow fuse and replaced it and still nothing, right? The magnetron is the most likely culprit...I would think it is safe to say that the magnetron shorted and drew enough current to blow the fuse.

Replace the magnetron and if that doesn't work, let me know here. Good Luck!

HI. in most cases, this will lead to a failed Heating device(magnetron tube).It would be wise to check the Magnetron cutoff fuse to be sure of its integrity. if the fuse is blown, simply replace it. if the fuse continues to show continuity, replace the magnetron.

(((The fuse is located inside the unit along side the magnetron)))

hi

power spikes are very damaging to a microwaves internal parts, it sounds like your transformer and/or magnetron are blown. if the unit is out of warranty I would reccomend getting a new microwave and also get a small single plug surge protector for it.

It could be a bad in-line circit breaker fuse. Unplug the microwave and take the outside cover off. Look for the in-line circuit breaker fuse. Use a plastic fuse puller (not your hands or a metal tool as there is still voltage stored in the microwave even when it is unplugged). Look at the fuse and see if it is blown. (The metal wire running length of tube will be broken. If you have one, test with an Ohmmeter.

The rectifier diode could indeed be bad. But first I would want to know what value (in uF) the old one was and what is the value of the new one? If they're too far off, the difference in the capacitive reactance could throw off the "tuning" of the circuit. The uF value of the capacitor is optimized in relation to the other components used in the system. Of course, you'd also want to be sure your new cap is at or slightly above the working voltage rating of the old one, too.