Tag: Repairs

If it used to work, it can work again

MTD Snowthrower Friction Drive Rebuild

During the last snowstorm of the season, the venerable MTD snowthrower carved a trench out of the garage and across the driveway, then abruptly stopped moving. The motor roared and the auger turned, but the drive clutch handle had no effect, so I dragged its carcass into the garage and we completed the mission by hand.

Popping the belly plate on the next sunny day revealed the problem: the jam nut (part 34) anchoring the Friction Disk Wheel (part 28) to the Friction Wheel Bracket Assembly (part 32) had gone missing:

MTD Snowblower – page 26 – friction drive parts

Worse, the Wheel’s threaded shaft spent some time rattling around in the Bracket while chewing up its thread:

MTD Snowthrower – friction disk wheel – damaged thread

This would ordinarily be No Big Deal, but what you see of the shaft is all you get: it rotates freely in the bearing embedded in the Wheel with no way to hold it while cleaning up its threads.

Having already promised to replace the Wheel, I installed the new Wheel using a castle nut secured with a generous dollop of red Loctite, then tapped two of its castellations into the shaft’s slot as a mechanical anchor:

MTD Snowthrower – friction disk wheel – castle nut

I really wanted to lay a nice hard roll pin along that slot through the nut, but there’s no convincing way to secure such a thing without a second nut. Maybe next time?

While I had the drive train apart, the sad state of the Wheel Shift Rod Assembly (part 29) became apparent:

MTD Snowthrower – wheel shift rod – worn

I scuffed up the shiny wear mark, turned a suitable acetal bushing, filled the trench with epoxy, and squished the bushing in place:

MTD Snowthrower – wheel shift rod – acetal bushing

The flange might hold it in place against the Frame Shift Bracket (part 18), which snugly contains the rest of the bushing against the epoxy, so the whole affair might outlast the next season’s first snowstorm. We shall see.

A nice new R-clip secures the Friction Wheel Bracket Assembly in place against the old washer:

MTD Snowthrower – friction bracket R-pin

You might want to insert it the other way, but the black plastic housing above it extends just far enough to thwart your (well, my) desire.

2022-04-25
Kukoke Outlet Timer: Over-powered Zener Diode

If the title seems familiar, it’s because there’s no visible difference (apart from the “brand name”) between the Enover timer that failed a little over a year ago and the Kuoke timer that recently failed:

Kukoke timer – overview

That’s what it looked like after the repair. Prior to that, it’s just a blank display with no response to any inputs.

Given identical hardware, the overheated phenolic PCB under the Zener diode came as no surprise:

Kukoke timer – zener heat death

As promised, though, this time I epoxied a brass shim heatsink to the new diode in hopes of cooling it enough to live long and prosper:

Kukoke timer – zener heatsink

I suppose I must now preemptively affix heatsinks in the two surviving timers, because we all know how their stories will end.

2022-04-22
Figaro TGS5042 CO Sensor

The hallway fire detector recently told us it scented carbon monoxide, but we hadn’t been doing any cooking or baking (in the kitchen two rooms away), the furnace (in the basement) hadn’t run for a few hours, and nothing else looked like it was on fire. I had recently replaced the alkaline batteries after a similar false alarm a few weeks earlier; it seems the detector failed after half a dozen years or so.

Tearing it apart revealed something resembling an 18650 lithium cell:

Figaro TGS5042 CO sensor – overview

Which made no sense, given the circuitry.

A casual search shows a Figaro TGS5042 is actually a carbon monoxide sensor. I’m mildly surprised enough gas gets through the vents fast enough to produce an early alert:

Figaro TGS5042 CO sensor – vent detail

I tore it apart to reveal a few droplets of whatever the electrolyte might be, so it hadn’t completely dried out.

The Product Information flyer doesn’t define what “long life” might be, but another page says “10 years”, so apparently the rest of the circuitry failed around a not-quite-dead-yet sensor.

2022-04-18
Kodak 750H Slide Projector: Tin Whiskers!
Mary’s folks asked me to figure out why the carousel on their Kodak 750H projector no longer turned. Some initial poking around suggested a problem with the solenoid, which only clunked when the projector was upside-down on the desk. I thought it might just have gummed up after all those years, but disassembling the thing (per the Service Manual and the usual Youtube videos) produced the root cause:

Kodak 750H Projector – broken solenoid link

That explained the yellowish plastic fragments rattling around inside.

As predicted, it’s impossible to remove the solenoid without breaking the equally brittle focus gear in the process:

Kodak 750H Projector – stripped focus gear

This is a sufficiently common projector to make repair parts cheap and readily available, at least for now.

Some of the interior sheet metal has a dark surface, likely heavy tin plating, covered with a thick coat of whiskers:
Kodak 750H Projector – tin whiskers
Kodak 750H Projector – tin whiskers
Kodak 750H Projector – tin whiskers
Kodak 750H Projector – tin whiskers
Touching a whiskered surface with masking tape captures the culprits, whereupon zooming the microscope and camera all the way in makes them just barely visible: they’re a few millimeters long and a few atoms wide:

Kodak 750H Projector – tin whiskers – detail

I have surely contaminated the entire Basement Laboratory with tin whiskers. Makes me itchy just thinking about them …
2022-04-14

B4-size Light Pad: Stabilizing the USB Connector

What used to be a “light box” had become a “light pad” powered through a USB Micro-B connector on the side. Unfortunately, the pad’s 5 mm thickness allows for very little mechanical reinforcement around the USB jack, while providing infinite opportunity to apply bending force. Over the course of the last half-dozen years (during which the price has dropped dramatically, despite recent events), the slightest motion flickered the LEDs.

So I squished the jack’s metal shell back into shape, found a short right-angle USB cable, and conjured a reinforcing fixture from the vasty digital deep:

The plate fits under the light pad, where a strip of super-sticky duct tape holds it in place:

LitUp Light Pad USB jack reinforcement - bottom — LitUp Light Pad USB jack reinforcement – bottom

The USB plug fits between the two blocks with hot-melt glue holding it in place and filling the gap between the plug and the pad.

I’d like to say it’s more elegant than the cable redirection for my tablet, but anything involving black electrical tape and hot-melt glue just isn’t in the running for elegant:

LitUp Light Pad USB jack reinforcement - top — LitUp Light Pad USB jack reinforcement – top

On the other paw, that socket ought to last pretty nearly forever, which counts for a whole lot more around here.

The retina-burn orange tape patches on the connector eliminate all the fumbling inherent to an asymmetric connector with invisible surface features. The USB wall wart on the other end of the cable sports similar markings.

The OpenSCAD source code as a GitHub Gist:

	// Bracket to protect USB jack on LitUp LED Pad
	// Ed Nisley KE4ZNU 2022-03-28

	Protrusion = 0.1; // make holes end cleanly

	Pad = [10.0,30.0,1.2];
	Plug = [8.0,10.5 + 0.5,8.0];

	BasePlate = [Pad.x + Plug.x,Pad.y,Pad.z];


	//———-
	// Create parts

	module Stiffener() {

	difference() {
	union() {
	translate([-Pad.x,-BasePlate.y/2,0])
	cube(BasePlate,center=false);
	translate([0,-Pad.y/2,0])
	cube([Plug.x,Pad.y,Plug.z],center=false);
	}
	translate([-Protrusion,-Plug.y/2,-Protrusion])
	cube(Plug + [2*Protrusion,0,Plug.z],center=false);
	}

	}

	//———-
	// Build them

	Stiffener();

view raw LitUp LED Light Pad.scad hosted with ❤ by GitHub

2022-04-07

Craftsman Hedge Trimmer: Biennial Laying On Of Hands Repair

Once again, the hedge trimmer failed to turn on with the switch pressed, so I took it apart, did nothing, and had thing start working again:

Craftsman Hedge Trimmer – innards exposed

It finally penetrated my dim consciousness: perhaps the switch is fine and a carbon brush (or two) has lost contact with the commutator atop a layer of oil and dust.

So a year from now when this happens again, try jamming a screwdriver through a vent slot and moving the motor a few degrees to jostle the crud.

If it works, that would be much easier than taking it apart!

2022-04-04
Garage Door Opener Battery Life

The keypad for the garage door opener didn’t cooperate one cold evening, so the first thing to check is the battery:

Garage Door Opener battery change

Given that it lacks a scrawled date, it’s the original battery dating back to late 1998 when I replaced the defunct opener that Came With The House™.

It was down to 8.3 V on that sunny afternoon and, surely, not nearly enough in the dark of a wintry night.

Even I can’t complain about that kind of battery life …

2022-03-18