Inverter microwave ovens - reliable?

I didn't know much about it. I bought one maybe 3 years ago. Small lightweight, and the most powerfull one I have ever had. I use it everyday. The only problem, the light does not come on when you open the door. My brother uses one in a resturant, and they have failed after much use. That one the commercial job, costs a lot more. Like I said, it small, powerfull, and cheap. My Sears GE microwave is big, not nearly as powerfull, also has turbo oven, but I use the Panasonic to heat fast. By other brother has a Samsung which has failed. Replaced diode and found the transformer is bad. After two months still waiting for transformer.

greg

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Maybe the reason the light does not come on is because it is burned out.

Since they're a relatively new technology (at least at the consumer level), my suspicion would be that, yeah, they are a bit less reliable.

There's also a bit of savings in lower freight costs from the lower weight. And smaller people (women in particular) tend to put some emphasis on the weight of their kitchen appliances, even if (as you point out) it's often completely irrelevant once you get the thing up on the counter at home.

"Joel Koltner" wrote in news:v1hrl.13379$ snipped-for-privacy@en-nntp-01.dc.easynews.com:

the savings is in not having to build an expensive,big transformer. all that copper is expensive,too.

transformers,being far less complicated,are more reliable. Inverters have a lot more components,particularly electrolytic caps,that increase the odds of failure. Many electrolytics are only rated for 3000 hrs or so of operation. and it seems that surface-mount electrolytic caps are even less long- lasting.

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Jim Yanik
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at
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Franc,

I don't think they're as reliable as conventional transformer/diode/ cap power supplies. "Inverter" is just a switching power supply that steps up the voltage, and consumer-grade SMPS in a variety of products have a rather high failure rate.

There were several threads on SER a few years ago when Panasonic first came out with the Inverter oves, about failures of the Inverter circuit. At that time, Panasonic wouldn't sell replacement parts for the Inverter power supply, or even provide a part number for the switching trasistors that were failing. You had to replace the whole power supply, which cost almost as much as a new oven.

The service manual for the NN-C2000 you linked to does have a parts list for the Inverter board, so maybe they are considered repairable now.

3 or 4 years ago, we needed a new microwave for the break room at work. Somebody donated an old (1984) Panasonic with a transformer power supply, and shortly thereafter a fancy new stainless-steel Panasonic Inverter microwave was purchased. The two were used side-by-side for just over a year, then one day I came in and saw the Inverter oven set outside for trash pickup.

So, I would definitely avoid the Inverter microwaves. Other manufacturers may be using switching power supplies, just not using the "Inverter" name. Last time I checked, most of the microwaves were still using transformer power supplies, but once the cost of a switching supply becomes less than a conventional supply, I would expect most of them to change over to SMPS.

When you go into the store, just lift up the right side of each microwave on display, and buy the heaviest one.

Mike WB2MEP

Aside from the reliability issues which have been addressed in other replies, it's possible that the HV diode died for reasons unrelated to the inverter.

What does the oven do when you go to "cook". If nothing at all, then there are almost certainly other bad parts, a fuse at the very least.

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On 03 Mar 2009 19:34:24 -0500, snipped-for-privacy@repairfaq.org (Samuel M. Goldwasser) put finger to keyboard and composed:

I'm not sure where to look except for the magnetron.

Page 20 of the following service manual has a detailed circuit diagram of the inverter:

Page 42 of this manual has a block diagram of the controller chip:

I didn't test it in case something else broke, but my brother tells me that everything appears to work except for the actual heating. That is, the control panel works, the turntable turns, and the fan spins. A shorted HV diode (there are two in a voltage doubler arrangement) would mean that one of the 8200pF caps is now connected directly across the secondary winding. I expect this would overload the transformer and presumably the inverter would sense this fault condition via the current transformer in the primary circuit. I'm told that the oven shuts down after a time. Anyway I've ordered the diode and I'll report back once I've tried it.

- Franc Zabkar

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The light comes on when its cooking. I usually carrry a flashlight so I can see the condition of the food.

greg

see the

That seems kind of obvious: door switch...probably gunked up with food residue.

jak

It never worked. I don't see any reason to not believe thats the way its designed. I need to hear from those who have these. But, one day I'll open er up and change it.

I remember way back on an old Norelco microwave, the controller failed, so I got out the old mechanical timer just like the one on my first Heathkit microwave. I can't stress how this simple and easy to use feature is missing on todays ovens. My father loved it. I think on better models they used aother timer to cycle the defrost. Those older models had at least 3 fail safe microswitches on them, but the switch took the full current. I'm sure in a fail safe mode, at least one microswitch in ALL microwaves take the full current.

greg

On Tue, 3 Mar 2009 15:57:41 -0800 (PST), Mike WB2MEP put finger to keyboard and composed:

The transistors are now offered as "A691E4V10GP Transistor Kit Series

2".

Here are the datasheets for the GT30J322 (75W) and GT60M303 (170W) IGBTs:

The oven has a rated output of 1100W. If the SMPS has an efficiency of

90%, then I expect that the transistors would be dissipating around 100W between them, although the mass of the heatsink appears relatively small for such a high heat load.

- Franc Zabkar

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see the

My sister had one like that; light on during cook -- no light with the door open. Dumb design.

I added a relay to solve the issue and was the big hero...

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On Wed, 04 Mar 2009 16:10:38 +1100, Franc Zabkar put finger to keyboard and composed:

I replaced the HV diode and all appears well so far.

- Franc Zabkar

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Hi!

I'm not sure I follow what you are saying. Are you saying that the microwave, when its controller went bad, failed in an "on" position? If I understand you correctly, I think it would be a far better idea to have the oven fail in an "off" position.

Older microwaves sometimes had multiple timers. My grandfather has a Litton microwave oven with two timers. One is the main timer, which is an analog "knob" on the front. The other "timer" is engaged and used in conjunction with the main timer when DEFROST mode is turned on. It consists of a slow turning motor that drives an irregular cam. When the cam rises up, it turns on a microswitch that enables the high voltage and magnetron.

Today, the controller board in a "typical" oven has two relays...one that runs the fan, turntable and light and another that can be turned on and off to cycle the magnetron.

I'm not sure how long that technique was used, as I have a slightly newer Litton microwave oven that is largely the same internally but has a "rolling digits" timer and a solid-state control board for the defrost and low power modes.

Newer microwaves also have multiple microswitches. (At least I have yet to see one that does not, and that's on ovens manufactured as recently as a year ago.) However, in normal operation, the microswitch that interrupts the oven's operation when the door opens is actually a low voltage signal to the controller board.

William

Microwave oven transformers are really quite undersized by conventional engineering standards for the amount of power going through them. Years of experience with the intermittent application and detailed electrical+mechanical+thermal engineering for some overtemp shutdowns is why they don't burn out despite being undersized.

I suspect that with some experience under the belt that the inverters can be made as reliable.

A lot of early consumer switching supplies weren't that good in their first iterations either - electrolytics was at least one cause of the problems.

Tim.

out:

Heh - there's a Buyer's Guide tip you will never see in Consumer Reports.

My favorite microwave oven is the Sharp "Carousel II" I pulled out of the trash in 1994. Replaced an open fuse for about 50 cents and it's been working fine ever since. I used that Sharp to replace a newer, smaller model with less capacity and never regretted that decision.

It's a shame how many of the older models I've seen tossed that only needed a fuse replacement.

Rick

out:

Still use our Sharp "Carousel II" from around 1987 and it's never even needed a new fuse. :)

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snipped-for-privacy@repairfaq.org (Samuel M. Goldwasser) wrote in news: snipped-for-privacy@repairfaq.org:

My Carousel from early 1980s blew the HV capacitor after about 20 yrs,replaced it and the HV diode for $25 several years ago,it's still running. The MWs of today don't have as tall a cavity as my Sharp's.

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But I suspect it's not as wide.