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.

Tag: Repairs

If it used to work, it can work again

Multimeter Probe Cable: FAIL

A reasonably good silicone-wire multimeter probe set arrived last spring and has worked well enough (I thought, anyhow) for the usual voltage measurements, but recently failed while measuring a small current. We all know how this will turn out, but the details may be of some interest.

Measuring the resistance from tip to plug located the fault to the black probe, after which I poked a pin through the insulation near the plug:

Multimeter probe – diagnosis

The two leads near the bottom go to my shiny Siglent bench multimeter. Despite their similarity to the failed probes, I’m pretty sure Siglent has better QC (well, mostly).

The probe’s resistance was near zero from the tip (offscreen to the left) to the pin and megohms from pin to plug (on the right). Figuring the wire worked loose, I pulled it away from the plug:

Multimeter probe – disassembly 1

Huh.

Although I wouldn’t have trusted those probes anywhere near their alleged 1 kV rating, seeing that exposed copper-like substance was disconcerting.

Hacking off the strain relief bushing around the wire got closer to the fault:

Multimeter probe – disassembly 2

And, finally, the problem becomes obvious:

Multimeter probe – disassembly 3

Yet Another Cold Solder Joint:

Multimeter probe – cold solder joint

Pulling a black banana plug from the heap, I decided to drill a proper hole to anchor the wire:

Multimeter probe – drilling plug

Which looked like this afterward:

Multimeter probe – soldered plug

And produced a strongly mismatched pair:

Multimeter probe – repaired

Ain’t it amazing how much fun you can have for a few bucks, all delivered by eBay? [sigh]

2019-01-04
Toy Cast Iron Stove Lid Lifter

This seemed appropriate for a day involving toys of all descriptions…

A cast iron stove (most likely a mid-last-century reproduction rather than a Genuine Antique™) emerged from a living room recess:

Toy stove with repaired lid lifter

The line across the lid lifter handle shows where it broke, long ago, likely while being played with. Back then, I’d done a static-display-grade fix with a dab of clear epoxy, but a better repair seemed called for; my repair-fu has grown stronger.

I expected the handle to be pot metal, so drilling a hole in both ends for a music-wire stiffener seemed reasonable:

Toy lid lifter – laser alignment

Much to my surprise, the carbide bit skittered off the surface, leaving fine swarf standing on the end. Turns out the lid lifter is cast iron, just like the rest of the stove!

Given that much of a clue, I aligned the pieces in a pair of machinist’s vises:

Toy lid lifter – alignment

Slide apart (the vises stand on a smooth glass sheet; the nubbly side is down), dab silver solder flux on the ends, capture a snippet of 40% silver solder in the gap:

Toy lid lifter – silver solder setup

Hit it ever so gently with a propane torch and slide together:

Toy lid lifter – silver soldered

The solder flows at 1200 °F = 650 °C, roughly corresponding to the blue-gray color near the joint. The nice purple (540 °C) on the left shows where I held the flame to start, with yellows (400 °C) on both sides. Good enough, sez I, it’s going to be a static-display exhibit.

Most of the solder went to the back side, so I filed it smooth and buffed off most of the heat coloration with a stainless-steel wire wheel in the Dremel:

Toy lid lifter – bottom

A little more wire-brush action left the front side looking good:

Toy lid lifter – top

As with most of the repairs around here, it simply makes me feel better …

Now, go play with your toys!

2018-12-25
Tour Easy Front Fender: Redux

The front fender on Mary’s bike snapped loose while we were on our way for groceries, but my repair kit ~~now~~ once again includes a few feet of duct tape and we continued the mission:

Tour Easy front fender – duct tape FTW

The final fracture seems to be just the little gray section amid the older fractures, so the Planet Bike clip was hanging on by a thread:

Tour Easy front fender – broken clip

Our bikes being equipped as alike as I can make them, another copy of the bracket I used on my bike sufficed:

Tour Easy front fender – new bracket

Stipulated: duct tape is déclassé, but it works better than anything else I’ve tried.

2018-12-24
Dell Laptop Battery Teardown

The defunct 18650 lithium cell I used for the DSO150 power supplyprompted me to crack open a battery from a long-gone Dell laptop to see if any of its cells were in better condition:

Dell laptop battery – case cracking

Yup, gently crushing it in a vise splits the case enough to work the Designated Prydriver around the joint, a process considerably simplified by the knowledge the case isn’t going back together again.

Prying the top off reveals the cells and their connections:

Dell laptop battery – circuitry

One of the cells had corroded, accounting for the pack’s failure:

Dell laptop battery – corroded cell

The others were undamaged, but had self-discharged down to about 1.5 V over the course of several years and refused to charge.

The moral may be to tear the pack apart as soon as it fails, a point always easier to recognize in retrospect.

So I taped the packs to prevent shorts and tossed them into the recycle box.

2018-12-20
Sonicare Essence: Final Battery Replacement

After a bit over five years, the NiMH cells in my ancient Philips Sonicare Essence toothbrush finally gave out:

Sonicare recharge dates – 2017-2018

Down near the end, the poor thing barely gave one brushing after an overnight charge.

While I was dismantling the case, I charged the last two new-old-stock NiMH cells:

Sonicare Essence – charging short cells

They arrived the same five years ago as the deaders in the toothbrush, but haven’t been used in the interim and charged well enough. The NiteCore D4 charger arrived after they did and isn’t really intended for 2/3 AA cells, so I used short brass tubes to make up the difference. I should have used the 300 mA low-current charging option (press-and-hold the Mode button for a second), although it didn’t overcook them at 750 mA.

The process went pretty much as before, with the new cells soldered in place atop the PCB:

Sonicare Essence – batteries on PCB

And the PCB tucked back into the case:

Sonicare Essence – batteries installed

I applied a solder bridge to the BLINKY pads, which seemed to disable the blinking and turn the LED on full with the toothbrush in the charger. Without waiting for a full charge cycle, I sucked the solder off the pads and restored the previous blinkiness.

A few strips of Kapton tape and it’s back in operation:

Sonicare Essence – retaped

The first charge lasted for two weeks, so things are looking good again. When the stock of knockoff replacement brush heads wears out, it’ll be time to get a whole new toothbrush … even if the batteries aren’t completely dead yet.

2018-12-19
Chair Reupholstering

We were tasked with replacing the foam cushion and seat covering on a pair of kitchen chairs. Removing the existing fabric seemed simple, until I pulled a dozen staples holding the cardboard cover to the bottom of the chair and exposed the fabric stapled to the MDF plate:

Chair reupholstering – stapled fabric

That’s just part of one corner. Obviously, whoever built the chair wanted to be very very very sure the fabric didn’t come loose!

Removing the staples from one corner produced a pile:

Chair reupholstering – one corner of staples

Piling up all the staples from the other chair looked even more impressive:

Chair reupholstering – staple pile

I fired maybe a third as many staples into the new fabric, which seems secure enough.

2018-12-18
Desk Drawer Stops

The stops aligning the top two drawers of an old desk vanished, so I got the job of replacing them. They’re hammered into the wood frame:

Drawer Stops – width measurement

And stand up just enough to engage the back of the drawer face:

Drawer Stops – height measurement

Back in the Basement Laboratory Shop Wing, I harvested steel strips from a defunct PC case, rubber-hammered them flat, sharpened a cold chisel (un-hardened, so it always needs sharpening), and got to work:

Drawer Stops – chiseled blanks

The pointy sides should have sharp edges, which you get for free with a chisel. You also get a bench full of little steel slivers perfectly suited for embedding in human flesh. Wearing eye protection is more than just a good idea, too.

Introducing what will become the visible edges to Mr Disk Sander makes them marginally less hazardous:

Drawer Stops – in progress

A slightly fuzzy picture of a test fit shows the stops should suffice:

Drawer Stops – trial fit

Which they did:

Drawer Stops – installed

Nobody will ever notice the blob of hot melt glue behind each one:

Drawer Stops – glue blob

Done!

2018-12-13