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Dissecting a malcontent (and moist?) microwave oven

9 min read

Again in February 2015, my spouse and I bought Whirlpool’s WMC30516AB 1.6 cubic foot microwave oven from Amazon:

It lasted a bit greater than 4 years. Towards the tip, varied segments of the four-digit, seven-segment per-digit show would flake out, then return, and random buttons on the entrance panel would additionally cease working solely to revive later. Finally, the resurrections ceased and, though the rest of the microwave oven presumably nonetheless functioned high quality, there now not was any technique to management it (notably through the no-longer-responsive “Begin” button).

So, we hauled it to the dump and changed it in July 2019 with…one other Whirlpool (what can I say, my spouse likes the model, or ought to I say preferred it), the familial WMC30516HV, this time for greater than twice the value of its predecessor at Home Depot:

Cease me in the event you’ve heard this earlier than: a bit greater than 4 years later, and round a month in the past, the alternative unit failed in precisely the identical approach. And in the event you search on-line for evaluations of both mannequin, you’ll discover that loads of different house owners’ items have suffered the identical destiny.

We’ve subsequently bought a Panasonic 2.2 cubic foot NN-SN966S in like-new claimed condition from Amazon’s Warehouse sub-site:

I’m comfortable to report that it was as marketed; I don’t assume it had even been taken out of the field by the unique purchaser (record worth: twice what we paid) previous to being returned for resale. However provided that we had two related-family Whirlpools die precisely the identical approach at near-exactly the identical time, the engineer in me suspected a elementary design flaw someplace. So earlier than taking this one to the dump…you guessed it…I made a decision to take it aside, partly as a result of extra typically I’ve all the time been inquisitive about what’s inside one in all this stuff.

My upfront suspicion was that moisture accumulation ensuing from poor air flow move via the unit’s inside whereas in use was backflowing into the electronics space of the system and finally inflicting one thing(s) on the PCB to fail. A part of this, I admit, could be our “fault”. I’m such a tightwad that if my spouse doesn’t end a Starbucks drink, I toss it within the fridge and warmth it up and drink it the following morning as a part of my every day caffeine consumption. Additional to that time, brewed espresso that we don’t end goes right into a carafe for me to later reheat and eat, too. Then there’s corn within the cob, soups, and loads of different moisture-rich meals and drinks that commonly discover their technique to the microwave for cooking and in any other case heating up…

However I’m not prepared to shoulder all, and even most, to be blunt, of the blame. For one factor, I don’t assume our utilization sample is all that atypical. And for additional proof of a possible elementary design flaw, try this case study example review of the WMC30516AB, full with submitted photograph and titled “Main steaming downside, and no assist in any respect from Whirlpool”, that I discovered on Amazon within the technique of finalizing this writeup:

This Microwave had a significant downside with steaming up, even with small prepare dinner masses like a number of slices of microwave bacon. This quickly led to apparent streaking and recognizing on the within of the (non-cleanable) viewing window. Whirlpool customer support was the worst half. They insisted that this steaming state of affairs is “regular efficiency,” although I’ve by no means seen one other microwave steam like this. I requested a service name to judge the Microwave however Whirlpool refused.

Come to consider it, I’d seen seemingly extreme inside condensation accumulation with our two items, too.

Sufficient preparatory chatter; let’s get to the teardown. Right here’s our affected person (for the majority of this undertaking, I’ve moved from my typical workplace desk to the workbench instantly under it within the furnace room for perhaps-obvious available-space causes, though the lighting’s not as stellar there):

Word that, in contrast to with my new Panasonic, there are not any outgoing airflow vents (both passive or energetic) on the left aspect. Maintain that thought:

Talking of airflow, the again’s the place the majority of the motion is:

Air is compelled into the unit by a fan behind the air flow gap mesh at left. It flows via the electronics, from there passively transitioning (theoretically, not less than) into the principle cooking cavity of the microwave oven, then once more passively out vent holes on the other higher aspect and again nook of the inside (higher proper aspect and again proper nook, from this photograph’s perspective). And the way does the air exit the microwave oven? By means of these passive vents you see at prime and on the best edge within the photograph, all on the again and on the best (once more, from this rearward perspective, not less than) half of the unit, principally making a 90° flip within the course of, once more, versus instantly out the other aspect with the Panasonic method.

Earlier than persevering with, a few close-up sticker pictures:

Now for the best aspect, these aren’t precise air vents, by the best way, solely beauty steel “trenches”:


And eventually, the underside:

Word that there are practical passive air vents right here, too, however their places are curious. They’re predominantly on the air-outflow half of the microwave oven, however because the air might be heated (albeit moist, due to this fact heavier than when it entered) at this level, and since sizzling air rises, not falls, I query simply how practical they are surely.

Again to the entrance; let’s now pop open the door:

The within of the door is standard for a microwave oven, so far as I can inform from my restricted, elementary expertise with these units (and shielded, after all, for apparent causes):

Once more, the airflow course via the inside is correct to left from this front-view perspective. That steel plate on the best aspect is a canopy for the waveguide, referred to as a mica plate:

A pair extra sticker closeups earlier than persevering with:

Earlier than diving in, I made a decision to fulfill my curiosity and see if the microwave oven’s several-week sojourn sitting downstairs unplugged and awaiting “surgical procedure” had left it reborn, as had occurred (quickly, not less than) previously. Nope:

The “8” entrance management panel button nonetheless labored, so you may inform which segments (of which digit) failed:

However most of the different numerical and practical buttons remained non-responsive…once more, together with the all-important “begin”. Oh nicely.

Onward. You’ll have already seen the big Torx head screw on the backside of the best aspect of the unit, and the 4 further ones across the edges of the again aspect. Let’s get these off:

With them eliminated, the unified right-top-left panel slides proper off the again:

From boring-to-exciting (IMHO) order, right here’s the now-exposed left aspect:

Prime aspect:

Full with warning (hah!) sticker closeup:

And the best aspect, the place all of the electronics motion occurs:

Your eye will seemingly be instantly drawn to the cavity magnetron on the middle, behind which (not proven) is the aforementioned waveguide:

That steel shroud to the best attracts in ambient air from the surface to maintain it cool. Talking of which, this doodad perched above it:

is, I’m assuming, a temperature sensor to determine whether or not the magnetron is overheating resulting from, for instance, utilizing the microwave oven with nothing inside it or with metallic contents.

Beneath the magnetron is a hefty transformer:

And to its proper is an equally formidable capacitor:

Within the higher proper of the sooner overview shot is a small PCB:

Presumably, significantly given the diminutive dimension of the onboard fuse, it does AC/DC conversion for less than a subset of your entire system circuitry.

And at far proper is the fan:

Now let’s transfer to the left aspect of that earlier overview shot. First off, right here’s the sunshine bulb, which shines via the passive air influx vents to light up the inside:

To its left and under are three elements whose goal wasn’t instantly apparent to me:

till I purposelessly pressed the latch to open the microwave door and seen that they’d additionally reworked in response:

These are, I consider, triple-redundancy switches meant to make sure that the magnetron solely operates when the door is closed.

Final, however not least, let’s take a look at the principle system PCB at far left, which is the upfront meant showcase (to not point out the presumed Achille’s Heel) of this undertaking:

Right here’s a barely tighter zoom-in:

First step: unhook the varied bits of cabling connecting it to the remainder of the system:

Two screws are instantly seen alongside the left edge. However eradicating them:

didn’t free the PCB from its captivity:

Wanting once more, I discovered one other one hidden among the many connectors, capacitors, and such on the best aspect of the PCB:

That’s extra prefer it:

Left behind, amongst different issues, is the oddly-varying-contact-color ribbon cable that initially routed between the PCB and the entrance management panel:

And right here’s yet one more wiring point out; referring again to earlier airflow feedback, I at first thought that the 2 wires heading beneath could be going to a air flow fan, meant to tug cool air into the physique cavity from the surface to the underside:

However after pulling off the underside panel to show the in any other case unmemorable under-interior to view, I spotted that they have been as a substitute related to (duh on me) the glass turntable motor:

Now again upstairs, the place the lighting’s higher, for the remainder of the PCB evaluation:

Let’s keep on with this latter aspect for the primary closeup shot set. Right here’s that faulty-segments show:

and the uncovered parts of this aspect of the PCB, dominated by solder factors and traces:

Did you discover, although, what seems like one nook of an IC protruding from below the show, additional uncovered after slipping off the encircling gasket?

Let’s see what some aspect views reveal:

Yep, there’s undoubtedly a big lead rely chip beneath. Happily, by unclipping two of the plastic “legs” from the bracket surrounding the show, I used to be capable of swing it out of the best way, revealing each its underside and the rest of this aspect of the PCB:

The shiny end atop the IC makes it very troublesome to learn (removed from {photograph}) the product markings, so that you’ll have to take me at my phrase that it’s a M9S8AC16CG microcontroller, containing an 8-bit S08 CPU, 16 KBytes of flash reminiscence and 512 bytes of SRAM, and nonetheless with its authentic Freescale Semiconductor vendor emblem stamp atop it (the corporate, due to this fact product line, have been later merged into NXP Semiconductors).

Let’s now flip the PCB over to its different aspect, beginning with some aspect views. Take a look at, for instance, that round “beep” piezo transducer close to the center:

And, wrapping up, a few full-on closeups, beginning with the highest half:

The 2 ICs you see at left are an I-core AiP24C02 2 Kbit EEPROM (what an EEPROM is doing in a microwave oven is past me, until it’s used for working dataset fine-tuning on the meeting line, or one thing like that) and, under it, an unknown-supplier LM358 twin 30V 700-kHz op amp.

Now for the opposite (decrease) half:

The clutch of ICs within the decrease proper nook includes two chips oriented 180° relative to one another and surprisingly stamped:

1730, preceded by an upside-down 7 in a bigger font dimension
817 C

and under and to the left of them, Power Integrations’ LNK364 AC/DC converter.

No apparent failure offender emerges from my visible inspection of the PCB; see something, readers? It kills me that the seemingly moisture- or heat-induced (one other potential aspect impact of poor air flow, after all) failure of a single cheap element on this board is probably going what brought about the demise of your entire costly microwave oven, however that’s our “trendy disposable society” for you, I suppose…Sadly, even when I may repair it, I’d be reluctant to go it on to another person with out a plethora of upfront qualifiers, as a result of it’d seemingly solely be a matter of time earlier than the unit died once more, resulting from its innate shortcomings.

With that, I flip it over to you on your ideas within the feedback!

Brian Dipert is the Editor-in-Chief of the Edge AI and Imaginative and prescient Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the corporate’s on-line e-newsletter.

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