Can a Microwave over lose power?

We have two microwave ovens in the kitchen. One is 24 years old and works wonderfully. The other one is only 5 years old but appears to be losing its microwave power. Originally, it would boil a cup of water in 60 seconds, but now takes in excess of 90 whereas the older of the two still takes 60 seconds. The newer one is supposed to be 600 watt whilst the older one is only 500.

Sure, microwave ovens can lose power over time. The magnetron can wear out, especially if you do things like put metal in the microwave or run it empty. The magnetron in a modern microwave isn’t as fragile as the ones were in really old microwaves (which would often break if you ran the oven empty) but they still can be damaged.

The power supply feeding the magnetron can also wear out, due to insulation breaking down or capacitors drying out and starting to fail.

Yes they lose output wattage all the time. One time I saw a tech testing the one in the tea room at work and asked him what he was doing. He explained how it worked and showed me his calculations.

Here is the method if you are interested.

I heard one of the causes of power loss is leakage into the vacuum, if you’re curious.

The single most common loss of power in a microwave is cruft building up in the microwave resonance cavity and waveguide. Stuff boiling off the food can drift up into it and start coating it a bit. Nothing a consumer can do about that after it happens.

This is why you always (loosely) cover stuff in the microwave.

There’s also some parts like big electrolytic capacitors that go bad.

And yes, the older ones were significantly more robust than newer ones. But since they cost maybe 50% more to make and last 4 times longer, we all know how that works out.

Interesting…recently, I started up the microwave in my mother’s summer house (the oven is 32 years old). Completely dead-no display, controls don’t work.
Is it worth fixing ? (Might be a bad transformer or power supply).

After 32 years, no. Get a modern microwave - more efficient, better design and way safer.

I’d be pretty concerned about leakage from a working 32 year old microwave.


Hey Ralph. i would suggest you disconnect it from the power and remove the outer cover. There should be a fuse that you can replace.

The mica screen that shields the wave guide is clean so I don’t think that it is gunk that is causing the low power. The old one has been used 10 times more than the new one and still works like new. Oh well the newer one is obviously just not made as well as the old one.

I doubt it would be due to the power supply, since if insulation failed, especially with 2,000 volts+, you’d most likely have a blown fuse, not reduced power, same for the capacitor (they use high-voltage AC oil-filled capacitors, which can’t dry out like electrolytics; if the oil leaked out, they would short out, which again leads to blown fuses; there is also a diode but again it is a no/go situation here). The magnetron definitely - it’s just a vacuum tube and will loose emission over time; figure a lifetime of several thousand hours.