CSI Electronica 2.1: Repairable Pair


Electric Avenue: Restoration edition

On the coat tails of our last feature, which featured a sampling of mortis electronica and a liberal distribution of death certificates, we’ve got a couple more electrical corpses on the table. If you are despairing over the throw-away nature of consumer electronics and appliances these days, fret no more. Electrical and electronic failures aren’t always fatal. This time, we’re going to bring back our patients. One surgery was straightforward. The other required creative thinking and an organ transplant, but looks and operates almost like the OE product. Neither was expensive, other than the time commitment.

As always, we limit the print article to a manageable length and save the goriest bits for our latest video feature. You can peer into that world by clicking below. If you enjoy what you see, would you take a moment to “like” the video, and subscribe to my channel? Those two actions help YouTube identify material to promote to other viewers with similar interests. If you prefer to hear the virtual clatter of a mechanical keyboard, scroll down to continue reading.

We can’t repair him, we don’t have the technology

Why are repairs, unlike standard pears, so rarely on the table these days? On one hand, low-cost, off-shore, contract manufacturing has enabled modern technologies to become cheaper and more widespread than ever before. Or, if not cheaper, than at least very widespread. But there are more than a few troubling side effects. One is that reparability has mostly fallen off the charts. Many modern devices get caught in the maelstrom of cost-saving techniques like surface-mount electronics, cheap plastics, and various plastic welding and glue-assembly methods. When a failure occurs, the dead device ends up in the scrap bin and the payer obtains another.

On a totally unrelated note: yes, we do still shop at Harbor Freight.

Contrawise, when an item is repairable, it usually requires replacing major subassemblies rather than just failed components. Many devices are so unlikely to be serviced that they are built in completely unserviceable configurations. The coffee grinder in our previous feature was one such example. Modern ultrabooks are trending this direction as well. And don’t even get us started on how Keurig single-serve machines are put together. About two years ago, regrettably not on camera, we disassembled a pair of failed brewers from the heart of Green Mountain and the components most likely to be serviceable were tightly bound in a Gordian knot of hoses, connectors, and brackets. Basic diagnosis wasn’t even practical without first unraveling the entire sweater.

Mostly dead is still slightly alive

In the fall of the year we experienced two more failures beyond those catalogued in our earlier feature. The first was an electric kettle (hotpot) that began cutting in and out before reaching full boil, but without tripping the release lever. The second was an LED tracklight module that stopped working, and wasn’t re-lampable.  Both of these items showed evidence of being repairable and the latter would be extremely inconvenient to replace, so we decided to use the screwdrivers a bit more gently than usual, in hopes that our disassembly work would be reversible.

We had high hopes for the kettle in particular. Simple electric heating appliances tend to score higher on reparability, because the requirement for high temperature and high-current operation favors old-time simplicity. That often means mechanical mechanisms and contactors. This particular example honored the old ways, and that meant we could attempt a corrective surgery. But first, a necessary disclaimer:

WARNING: We are partially demonstrating the disassembly and modification of a 120 VAC, mains-connected appliance. Such work can be hazardous to life and property, and may reduce or disable the original equipment safety features. You should not attempt this or similar work unless familiar with safe procedures for servicing mains-connected equipment. This article is for information and entertainment only. Any attempt to use this information for other purposes is solely at your own risk. In some countries, local laws may not permit an unlicensed person to repair or modify mains-connected equipment.

Base removed. Heating element is embedded in the C-shaped channel.

Upon initial removal of the base cover, we see the on-off lever mechanism’s relationship to the power connector and the heating element. Normally, only the center circular assembly is visible from the bottom side, since that’s the part which sits on the electric base. The high-level explanation is that after power enters that connector, the lever switches two mechanical contacts which feed power to a resistive heating element embedded in an aluminum casting.

But since this isn’t 1960, our electrical appliances also have extensive safety mechanisms that require a closer look. After further disassembly and examination, which can be observed with more angles and detail in our video, we worked out the basic components visible from the bottom side:

The mechanism viewed from the bottom side (i.e. facing the electric base).

We see the power inlet pin and sleve, which make contact with recessed contacts inside the baseplate assembly. These permit the kettle to be easily lifted from and returned to the base in a way that doesn’t expose the user to an electric hazard. The two mechanical contacts, operated by the lever, are also visible. We further see a “safety release” button. This button must be depressed for the operating lever to latch. Removing the kettle from the base while switched “on” forces it “off,” and it cannot be latched to “on” while removed from the base. Unless, of course, someone with a screwdriver overrides it for a video demo.

Let’s turn the assembly over:

Flipping the mechanism over reveals additional operating features.

Looking at the opposite side of the mechanism, we first see see the spring that “loads” the lever, the steam tube exit from the pot, and the steam release port with a bimetallic plate partially visible inside. The steam tube feeds through the pot to the top of the interior chamber. When the water reaches a rolling boil, steam heat pressurizes that tube slightly and releases a bimetallic trip plate. The trip plate is the second means for releasing the “on-off” lever. As a clear demo, if the pot is boiled with the lid open, the tube won’t pressurize and it will continue to boil.

What prevents a serious overheat? That’s where the overheat regulators come into play. These are also bimetallic metal plates that warp in response to high temperatures. However, instead of releasing the lever, these each push on a pin over one of the two switch contacts to temporarily break the circuit. When the base cools sufficiently, the bimetallic plate returns to its normal shape and releases the pin, visible in a side view:

Regulator side view showing the contact-release pin (in white).

The pin opens the mechanical power switch contact below. This allows the pot to regulate the base temperature in an overheat scenario, particularly if the pot boils dry or is started without water inside. In our case, we think these were kicking in early due to metal fatigue. After countless thousands of operations, the metal had weakened and was hitting the interrupt pins within a normal temperature range.

Our solution? Bend the strips upward slightly with a needle-nose pliers, restoring some of the lost springiness. Problem solved…for now. After slightly loosening everything up by disassembly and tweaking, the contact assembly probably won’t last forever with this repair. We have already purchased a replacement to store against the inevitable. But since the replacement pot has a lower wattage and heats slower, we’re still using this one until it dies permanently.

We might note, though, that with low-cost power electronics being everywhere, odds are good that the next time we dive into an electric hotpot, the boiling element could prove to be a high-frequency induction type heater, driven by yet another surface mount circuit and a pair of conformal-coated MOSFETs. When that day comes, this repair technique will be another obsolete trick consigned to history’s dustbin.

We got more in the video feature

Our second repair, the overhead LED light fixture, ended up becoming a total conversion project. In spite of that, it was a surprisingly inexpensive one, thanks to a bit of creative thinking, and still looks completely OEM from the outside. Check out our YouTube video feature to see how that went, and maybe get a few ideas for your own household repair projects.

Meanwhile, thanks for joining us here in the print world. Until next time, repair onward when you can, but stay within the safe boundaries of your skillset. See you then!

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Aaron Vienot

Engineer by day, hobbyist by night, occasional contributor, and full-time wise guy.

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3 months ago

Repairability is why I keep my old grand piano going and avoid electronic music devices. I used to tune and repair pianos, still have the tools. Repairing an instrument is enormously satisfying.

4 months ago

That’s nothing! Let’s repair the oil heater given nothing but an ancient control valve I dug up when cleaning up trash.

Aaron Vienot
4 months ago
Reply to  chuckula

Get on it, then! It’s cold outside.

4 months ago
Reply to  chuckula

not even “ancient” probably take you 10 minutes to get it all working again

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