Mind over Matter: Stuff I cared about at the time

Design for Serviceability

Panasonic Microwave

About an hour into a brief, twenty-four hour getaway, I received a not quite panicked call from my mom, letting me know that her microwave (a Panasonic NN-SN733W, bought in August 2015) wasn’t working. She uses the microwave all the time, for heating up water to make tea, and even making a good percentage of her meals. It’s probably the most used appliance in her apartment. Which is mildly ironic, considering how dubious she was of the idea when I bought her her first one. She was a bit disappointed that I wouldn’t be able to deal with it that day, but in the end was accepting of the situation.

So today, after coming home, one of the first things I did was to take a look at her microwave. And as she had told me, it seemed completely dead — no clock, no light, no nothing. The outlet it was plugged into was good. I explained that generally appliances don’t fail like that. Maybe the turntable motor would fail, or the magnetron, or the control panel. But given that there was zero sign of life, it seemed likely that it was an internal fuse that had blown. So, I began to take it apart. There was one Phillips screw on the bottom of one side holding the shell of the case on, which I removed. But the other half-dozen screws were all security Torx screws! A sign that the manufacturer definitely didn’t want a consumer opening it up (but why have the one plain Phillips? That is a mystery…).

When I got it open, I could see that the power supply circuit board did indeed have a fuse on it, and the fuse was in a fuse holder, rather than being soldered to the board. Hallelujah! There was hope! It was a ceramic fuse, though, so it wasn’t immediately obvious whether it was blown or not. But a quick check with an ohm meter showed it had blown.

After returning from the hardware store, about 10 minutes later, I popped the new fuse in, and plugged it in briefly, just to see if the clock would come on, etc. And sure enough it did. So, I unplugged it, put everything back together properly (or nearly so), and had mom try it by heating a cup of water. And it worked! So, all is good, at least for the time being, and another microwave has been saved from the landfill/incinerator.

But this begs the question — why?? Why make it so that the average consumer couldn’t replace the fuse? Why not make the fuse accessible without taking the whole shell off? A fuse is, or should be, a “user serviceable part.” I can’t quite imagine what the rationale is for making it this way. Is it in the hopes that people will just toss it and buy another? Why not solder the fuse to the board then? Is it to help keep appliance repair shops in business? Seems vaguely plausible, but unlikely.

I do have the sense that a generation (or two…) ago, people were more accustomed to fixing some things themselves. I am also aware that those “things” were significantly simpler then. An electric stove had a power cord, and from there, the wires went to a bunch of resistive heating elements through a simple, electromechanical control, turning on and off various combinations of heating elements. And a thermostat for the oven. If there was anything else, it was a clock that operated on the 60 Hz AC signal. There were no circuit boards with touch panels, and fluorescent displays to break, which would have to be replaced in whole if something failed. But a fuse? Why bury that where it is unlikely to be discovered except by the most intrepid of owners. While I do appreciate the forward leaps we’ve experienced in functionality, I do believe a lot more could be done to make appliances more serviceable.



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2 responses to “Design for Serviceability”

  1. John Kohl Avatar
    John Kohl

    I’d first ask, what could have caused the fuse to blow? I recently had to replace a transformer on my home HVAC system, but before that we had to find what had failed…it was a rodent incursion into the A/C compressor relay that short-circuited something and overloaded the transformer. So we replaced that relay, and then the transformer.

    The other thing about microwave ovens is the high-voltage side of things that drives the magnetron. Perhaps the manufacturer doesn’t want that section serviced by untrained personnel?

    1. admin Avatar

      Don’t rightly know what caused it. There was certainly nothing obvious, like rodent (or insect) damage in there. My feeling was, if a second fuse blew in short order, it would either be time to dig deeper (not sure I feel qualified on that front) or send it to the landfill. I’m sure you’re right, that they don’t really want anyone *anywhere* in there, but fuses on many types of electrical gadgets used to be more accessible, and I feel that hiding them away does a disservice to consumers. If there was a real fault, a second fuse is going to blow as well. In my experience, internal fuses blow more frequently because of age, or some other internal defect, than because of the type of overload they are there to protect us from. At least, I am challenged to conclude otherwise, given my success in replacing blown fuses with new fuses (same rating, of course! Not cheating here!) and suffering no further ill effects. Ah well, in the end, a success story, and justification for purchasing the set of security driver tips I bought probably 20 years ago and never had cause to use until now!