The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Category: Home Ec

Things around the home & hearth

Samsung Refrigerator Condenser Coil Cleaning
The kitchen came with matched Samsung appliances dating back to 2018 and, on a frigid winter day, we piled the contents of the freezer on the porch and gave it a deep cleaning. While the empty freezer was cooling down from its adventure, I wondered:
- Where were the condenser coils were located?
- Did they need cleaning?
- How does one do that?
The manual is strangely silent about even the existence of the coils, so evidently cleaning them wasn’t of any importance to Samsung.

Rolling the refrigerator away from the wall just enough to get the phone camera down there suggests they exist and are in need of some attention:

Samsung refrigerator coils – first sight

Rolling the refrigerator out until the door handles met the countertop across the way let me climb over the counter and worm myself into the refrigerator-sized hole behind it, bringing along a screwdriver, the vacuum cleaner snout, and a few brushes.

Removing five screws released the back cover:

Samsung refrigerator coils – cover off

Looking into the intake end of those coils (on the right):

Samsung refrigerator coils – first intake view

So, yeah, I’m about to give them their first cleaning ever.

Five minutes of brushing fuzz, mostly into the vacuum, cleared a good bit of the exterior, but the interior needs more attention:

Samsung refrigerator coils – partial clean

Ten minutes later:

Samsung refrigerator coils – victory

Another five minutes:

Samsung refrigerator coils – intake cleaned

Making the coils cleanable and putting them where they could be cleaned were obviously not bullet-item goals for Samsung’s designers.

Although the coils are not perfectly clean, I don’t know how to get them any cleaner, despite knowing even a thin layer of fuzz kills the refrigerator’s much-touted energy efficiency. Perhaps blowing them off with compressed air, then cleaning a thin layer of dust off the entire kitchen, would help.

I think the refrigerator will be happier, at least for a while.
2025-01-16
Quick-n-Easy Window Shade End Cap
While tracking down an air leak in a living room window, I noticed one of the cellular blinds was missing an end cap, so I scanned a pair of surviving caps:

Living Room shade end caps – level adjust

Blow out the contrast, save as a JPG.

Import into LightBurn:
- Trace the outlines into paths
- Use LightBurn’s shape optimization tool to dramatically reduce the number of nodes & smooth the outlines
- Overlay & align the shapes
- Export as an SVG file
Import into Inkscape:
- Put the paths on named layers
- Center around an alignment mark
- Save as an Inkscape SVG
Living Room shade end caps – Inkscape alignment

It is slightly tilted, but that doesn’t matter. You could devote more time to smoothing / reverse-engineering the shapes, but that doesn’t make much difference, either.

Inkscape exports the SVG coordinates with respect to the overall page origin in the lower left corner, so when OpenSCAD imports the SVG the paths end up far away from the origin. The trick is to put a 2 mm diameter circle at a known location, center the paths around it, then have OpenSCAD use the circle’s location to recenter the paths.

Because Inkscape uses the lower left corner of each shape as its origin, you must put the circle at (99,99) to have its center at (100,100). That is one of the many reasons you (well, I) can’t use Inkscape as a CAD program.

Import into OpenSCAD, recenter, and extrude the shapes:
```
CapCenter = [100,100];

PlateThick = 1.8;       // thickness of visible end cap

HolderTall = 10.0 + PlateThick;

union() {
  linear_extrude(height=PlateThick)
      translate(-CapCenter)
            import("Living Room shade end caps - Inkscape.svg",layer="Exterior");
  linear_extrude(height=HolderTall)
      translate(-CapCenter)
            import("Living Room shade end caps - Inkscape.svg",layer="Retainer");
}
```
Which produces a solid model:

Living Room shade end caps – solid model

Save the model as 3mf, import into PrusaSlicer, and slice:

Living Room shade end caps – PrusaSlicer preview

Making the retainer shape a little wider would be a good idea to get better infill, but it’s a slip fit into the blind (surely why it fell out long ago) and need not withstand any stress.

Print as usual:

Living Room shade end cap – on platform

And then It Just Works™:

Living Room shade end cap – installed

It’s sitting atop a bookcase while I finish tinkering with its window.

All that seems like a lot of fiddling around, but it uses each program to its best advantage and it’s surprisingly easy after the first few models.
2025-01-09
Handi-Quilter HQ Sixteen: Preliminary Power PCB Schematic

Because I must eventually diagnose and fix the HQ Sixteen’s Motor Stall Heisenbug, I printed out several views of the power supply PCB on glossy photo paper for best visibility.

The component side:

Power PCB – components

The solder side:

Power PCB – solder

The X-ray view:

Power PCB – overlaid

Considerable pondering and sketching produced an annotated view of the solder side:

HQ Sixteen – Power PCB – solder side – component labels – reduced

Here’s a tentative schematic drawn on the fly while extracting it from the PCB traces:

HQ Sixteen – Power PCB – rough schematic

!!CAUTION!! I have not verified the schematic against the actual hardware / PCB / components, as the Heisenbug has not reoccurred and I had no occasion to take the machine apart for checking. Do not assume any connections or components are correctly drawn.

Before I redraw the schematic in a more useful format, I must verify several nodes, because not everything in there makes sense.

In particular, the elaborate resistor string in the middle of the page seems to establish reference voltages for everything else, from the motor power supply turn-on delay to the RUN signal starting the motor.

The optoisolators definitely get the RUN command signal from the controller and feed the STALL motor status back to it. That’s assuming I understand enough to pin those labels on those connections.

!!CAUTION!! Read my caveats about the direct-from-the-AC-line non-isolated +160 VDC motor supply before connecting your instruments. The GND traces are not isolated from the AC line and are not at the normal “0 V” AC neutral potential.

But if this mess gets you further along with whatever you were doing, let me know how it all worked out for you.

2025-01-08
Christmas Non-Wrapped Box
Mostly to find out if I could do it:

Christmas Wrap custom box

The process:
- Fetch a printable wrapping paper pattern, ignore the watermark
- Resize / crop to fit a Letter page, print two copies on glossy photo paper
- Generate a suitable multi-sheet paper box in SVG format
- Import into LightBurn
- Rearrange / splice the parts to put the main box on one Letter size sheet and the end caps on another
- Fire The Laser to score (blue lines) and cut (red lines) the paper
- Assemble using a glue stick
- Fill with Christmasy stuff (your choice may vary)
- Tuck the flap, there’s no need to wrap!
The rearranged main box just barely fits across a Letter page:

Non-Wrapped Christmas Box – main piece – LightBurn layout

You can make many more end caps than you need:

Non-Wrapped Christmas Box – endcaps – LightBurn layout

Obviously, this makes no sense whatsoever in terms of box making, but the recipient smiled and that’s what I wanted.
2025-01-02
Vole Traps: End of Season

A highly effective way to bait a rat trap for garden voles:

Rat trap – still baited

The trap is a Victor M205 (in a 12-pack as M326) with a big yellow plastic bait pedal. The bait is pieces of walnut, secured to the pedal with generous strands of hot melt glue. The trick involves mechanically capturing the walnut by slobbering glue over & around it, forcing the vole to pull & tug while gnawing the last bit of goodness.

Which generally ends badly:

Rat trap – gnawed bait

I do not begrudge the critters a fancy last meal; it’s gotta be better than their usual diet of carrots / radishes / turnips.

Voles have no qualms about eating the bait from a sprung trap with a dead compadre a few millimeters away:

Rat trap – empty bait

They will sometimes eat the walnuts and their dead compadre.

The plastic pedals work much better than the old-style metal pedals at holding the steel arm wire. The wire slides freely on the plastic, in contrast to the previous high-friction metal-on-metal latch.

Some of the traps were entirely too sensitive and required slightly bending the tip of the arm wire upward to increase the friction on the plastic plate. Always always always handle armed traps by the wooden edges beside the kill bar, so when it accidentally snaps your fingers are nowhere near the business end.

After I figured out how to properly bait the traps and we set out half a dozen traps in the most attractive crops, Mary’s garden produced 54 dead voles over the course of 90 days, sometimes in groups of three or four at a time. While this did not prevent all the crop damage, it definitely reduced the problem.

Next year we’ll start early and probably reach triple digits by midsummer.

The same technique with Victor M035 mouse traps (in 12-packs as M035-12) is brutally effective on house mice.

2024-12-06
Quilting Ruler Rack: Expedient Base

Mary is at least the third owner of a steel rack, originally intended to hold packages of retail stuff, which now holds (much of) her collection of quilting rulers:

Quilting Ruler Rack Base – overview

Obviously, it was never intended to hold heavy acrylic sheets, but it worked surprisingly well, right up to the point where too many of the rulers collected on two adjacent columns of pegs and overbalanced the whole affair atop her while she attempted to remove a ruler.

Subsequent accident recreation showed the rack toppled when the weight of the rulers on the two adjacent columns of hooks moved the center of mass outward, just inside the line between those feet, whereupon the slightest tug on a ruler pulled it over.

Measurements revealed the four legs do not sit on a square contact patch, are not parallel to the radii from the center point, and are not uniformly distant from the center. Rather than committing to a finished product, I made a cardboard prototype to verify a bigger base would solve the problem and I could capture all those feet.

You don’t have such a rack, so the exact dimensions don’t matter, but the LightBurn layout looks like this:

Quilting Ruler Rack Base

The disk is two cross-laid sheets for stiffness, with marks burned on the top to help align the feet more-or-less around the center point.

The oblong rings fit around the feet to capture them, so cut eight or twelve to make four stacks a bit taller than the wire diameter.

The H shape then glues atop the rings to hold the feet in place. They’re not removable, but a razor knife will eventually solve that problem.

I slobbered hot melt glue across the cardboard disks to hold them together, glued and aligned the rings where the feet dented the disks, stood the rack in the rings, and glued the H plates.

About an hour elapsed from the sound of the crash to the rack once again standing quietly beside the fabric cabinets.

We’ll run this for a while and eventually replace it with a plywood disk and screwed-in-place clamps for the feet, which will surely call for wood surface preparation / stain / seal treatment.

2024-11-27
Sears Microwave: Laying-On of Hands Repair

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.

Somebody give me an Amen!

2024-11-25