Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Judging from the dates codes on the ICs inside, Mary’s HandiQuilter Sixteen long-arm machine is about two decades old and many of the white LEDs in the front handlebars have gone dark:
HQ Sixteen – dead handlebar LEDs
The vertiginous view looks upward into the handlebar at the top of the machine (more on this later). The PCBs run strings of three series LEDs from a 16 VDC supply with a 390 Ω ballast resistor (oddly enough, on the ground end of the string), so one failed LED takes down all three.
I decided to replace all the LEDs, on the principle they’re surely dimmer than they used to beand to take advantage of a decade or so of improvement in white LEDs (yes, I have old stock).
After discovering that the HandiQuilter engineers violated the Principle of Least Surprise by orienting adjacent LED strings in opposite directions, I found one of the strings still didn’t light up.
Pop quiz: which one of these LEDs caused the problem?
5 mm LEDs – swapped polarity
To the best of my knowledge, all 5 mm round LED packages mark the cathode lead with a flat edge. It’s easy to remember, as the cathode side of the schematic symbol has a bar: straight bar = straight edge.
Inside, the LED chip’s cathode lead is bonded to the reflective cup, with the anode lead wire-bonded to the top.
Took me a while to see what was wrong, too.
For whatever it’s worth, the backward LED works fine.
Although essentially all kitchens feature a microwave over the stove, essentially all women have difficulty reaching it. As a result, our kitchen has two microwaves: the built-in Samsung over the stove and our trusty Sears Kenmore on the counter.
We’ve had it for a while:
Sears Microwave – data plate
Apart from the turntable rollers, it’s been utterly reliable for the last two decades, until the Start button stopped working:
Sears Microwave – control panel
The membrane switch panel seems to be in good shape, with no cracks in the plastic surface. Only the Start button failed, which suggested the switch contact pad had failed and ruled out broken matrix traces on the flexible circuitry.
Back in the day, they kept casual tinkerers out of the dangerous interior:
Sears Microwave – Torx security screw
That would not be me:
Sears Microwave – security bit set
Over the course of two decades, an occasional food explosion produces a surprising amount of debris:
Sears Microwave – exhaust vent spatter
Go ahead, I dare you, show us your microwave exhaust vent.
The control panel circuit board & wiring looks like this:
Sears Microwave – control board – in place
Unplugging all the connectors proceeds as you’d expect, whereupon a single screw (out of sight to the top) releases the control assembly and pulling the whole thing upward gets it out of the cabinet:
Sears Microwave – control board
The capacitors show no signs of The Plague, but those resistors near the optoisolator (?) in the middle have a suspicious thermal plume.
The ribbon cable from the control surface goes into a connector with the usual locking collar:
Sears Microwave – control panel cable connector
The cable also has cutouts latching into tabs molded into the collar:
Sears Microwave – control panel ribbon cable – locking tabs
Removing two screws at the transformer releases the PCB:
Sears Microwave – control panel interior
Which promptly slammed the whole repair mission to a dead stop: with the entire membrane switch assembly glued to the front of the plastic shell, there is no way to get to the Start switch. Trying to peel the membrane off will most certainly destroy it.
Because all the other functions still worked, including the Add Minute button, we figured we can eke out a few more years before something else fails or the lack of one button gets intolerably annoying.
I reassembled everything in reverse order, plugged it in, and, while setting the clock, discovered the Start button once again worked perfectly.
It’s a classic laying-on of hands repair: take something apart, replace nothing, reassemble, and it works!
If the Start button is not part of the overall switch matrix, with a separate conductor through the ribbon cable, un- and re- plugging would be enough to restore a flaky contact. We’ll never know the rest of the story, although with this post as a reminder, maybe I can remember to tear the matrix apart when we scrap it out.
A power transmission line (probably 115 or 138 kV) runs along the Casper Creek (f.k.a. Casperkill) and through the Vassar campus beyond our back yard, which accounted for a loud roar one morning:
Helicopter power line inspection
The pilot hovered above each pylon long enough for the inspector seated in the open door to do whatever needed doing:
Helicopter power line inspection – clear view
A casual image search suggests it’s an MD520N (N = NOTAR = “No Tail Rotor”) helicopter. Although the NOTAR back end produces much less noise than an exposed rotor, it was plenty loud enough a few hundred feet away.
Folks who know more than I do about helicopters pointed out the tail rotor I didn’t see. Here’s a tight crop from another image with the rotor in plain view:
An entry from The New Garden Encylopedia, copyright 1936 through 1946, gives recommendations for using arsenical poisons in your garden:
Arsenical poisons
My father always said anybody who talks fondly of The Good Old Days wasn’t alive back then. He was and thought things had definitely improved since then.
Having watched a tour bus jounce over the poor suffering street lamp base, I can easily understand how something similarly large killed the street signs:
Street Lamp Base – Overview
The black ring in the upper left formerly positioned a barrel over the lamp base:
Street Lamp Base – barrel ring
Something heavy shaved down those bolts:
Street Lamp Base – detail
The blue-and-white pull cord seems at risk of vanishing.
They’re now laying asphalt and the project continues apace.
The Smell of Molten Projects in the Morning 