Tag: Improvements

Making the world a better place, one piece at a time

Whirlpool Refrigerator Drawer Slide: Another Bracket

Thirteen years after the original repair on the left side and eight years after I fixed the drawer slide on the right side, this happened:

Refrigerator shelf slide – failed parts

The general idea is to wrap a new bracket around the old bracket, because trying to remove the old one will probably cause more damage:

Refrigerator shelf slide – trial assembly

A pair of screws hold the new bracket to the shelf support:

Refrigerator shelf slide – support screw nut openings

Those two screws must support the entire weight of the drawer, which is exactly what broke the original all-plastic frame and slide.

The epoxy chip and transparent plastic sheet in the first picture spaced the old aluminum bracket away from the shelf support and reduced the space beyond the new bracket enough to require drilling access holes. Fortunately, they’re hidden inside the support frame, so nobody will ever know.

The shelf support is a huge floppy rectangle, so I clamped it to the bench vise while drilling the holes:

Refrigerator shelf slide – upright vise clamp

The new bracket is on the right, with a sheet of white acrylic spacing it away from the shelf support by exactly the same distance as the angled aluminum snippet replacing the failed epoxy & plastic on the broken part:

Refrigerator shelf slide – bracket parts

The two holes in the middle of the aluminum parts show that I used exactly the same angle brackets as raw material. It’ll be a sad day when I eventually use the last of those brackets.

Putting the parts together, with double-stick tape holding all the parts in place, shows how they fit:

Refrigerator shelf slide – repair trial assembly

And then it just snapped into place. I didn’t bother pretending solvent glue would help anything, nor did I apply any epoxy, so this whole thing hangs from those two 4-40 screws. On the other paw, their steel beats the original white plastic.

I devoutly hope to never rebuild the actual drawer slide, but these dimensions may help somebody else out of a jam:

Refrigerator shelf slide – dimensions

The vertical “40” dimension refers to the available space from the bottom of the white plastic part to the top of the shelf support frame; the new bracket is a tad shorter than that.

The plastic parts in that refrigerator have been a complete disappointment: were it not for my relentless repair jones, we’d likely be on our third or fourth refrigerator by now. Oddly, the cooling parts continue to chug along (*), without more than the occasional loud noise in the middle of the night.

We’re definitely doing our part to reduce our waste stream.

(*) The most recent freezer fan hasn’t failed yet!

2017-10-05
60 kHz Preamp: Filtering and Rebiasing

The LT1920 instrumentation amplifier now sports two silver-mica caps on its inputs as a differential-mode input filter cutting back strong RF signals (clicky for more dots):

60 kHz Preamp Schematic – DM filter inst amp – BP filter rebias – 2017-09-22

In principle, a DM filter should eliminate RF rectification from out-of-band signals, although I think the attic is quiet enough to not need any help. The caps form a simple RC LP filter rolling off at 5.490 kΩ × 150 pF → 193 kHz, high enough above the 60 kHz signal to not make much difference down there.

The silver-mica caps come from the Big Box o’ Caps, which contained an envelope with a few large 150 pF ±1% caps and a bag stuffed with similar 147 pF ±1% caps. Mixed in with the latter were some smaller 147 pF caps (*) of no particular tolerance (perhaps 5%), from which I neurotically matched a pair to 0.05 pF without too much effort. Doesn’t matter, given the other tolerances and suchlike, but it was amusing.

I’d inadvertently grounded the cold end of the 330 Ω input resistor in the LM353 bandpass filter, now properly tied at the Vcc/2 virtual ground to take the DC load off the LT1920 output: a 100 nF cap (27 Ω at 60 kHz) stores the bias level without messing up the filter shape.

A similar cap rebiases the protected resonator at the LT1010 buffer input:

60 kHz Preamp Schematic – protected resonator – output rebias – 2017-09-22

The new caps aren’t all that visible and the resonator vanishes in the clutter:

60 kHz Preamp – protected resonator filter – overview

Next: find out how well it works!

(*) Yes, there were two envelopes between 150 pF and 147 pF:

Silver-mica caps

2017-09-29
60 kHz Preamp: Power LED Resistor Oops

I eventually noticed the yellow LED indicating +24 V input from the power supply (previously, a noisy wall wart) was dark. Poking around revealed I’d inadvertently installed a 1 kΩ ballast resistor:

LF Preamp – burned power-on LED resistor

A 1/4 W resistor can’t dissipate half a watt for very long, as shown by the discolored circuit board around the leads and the faint smell of electrical death in the area.

I swapped in a 3.3 kΩ resistor, the yellow LED lit up for a few seconds, then went dark again. This time, the LED was dead; apparently, it’d been overstressed for long enough to fail. I can’t be too annoyed.

Unfortunately, replacing the LED required removing the entire housing with all three LEDs, chopping off the defunct block, reinstalling the attenuated block with the two green LEDs, installing a similar red LED, and finally installing a nice 3.3 kΩ half-watt resistor:

Power LED – Red with 0.5 W resistor

So it goes …

2017-09-28
60 kHz Preamp: Tuning Fork Resonator Protection

Limiting the resonator drive to about 1 μW in the face of wildly varying RF from the antenna (or the occasional finger fumble) requires brute force. A nose-to-tail pair of Schottky diodes seems to do the trick:

Tuning Fork Resonator Filter – protection and biasing

The 100 Ω resistor blunts the drive from the LM353 op amp (implementing a bandpass filter) when the signal peaks exceed 200-ish mV in either direction from the Vcc/2 bias stored in the 10 μF cap.

The 11.5 kΩ resistor downstream of the resonator isolates it from the Vcc/2 bias, with the 100 nF cap sinkholing the signal and the 4.7 kΩ resistor preventing feedback into the bias supply. The cap looks like 26 Ω at 60 kHz, so the feedback runs -52 dB from the output and the bias supply knocks it down a bit more. The preceding amps apply 40-ish dB of gain from the antenna terminals, so the loop gain looks OK.

It’s another few components on the board:

LF Crystal Tester – resonator protection

The blue twiddlecap should allow pulling the tuning fork’s series resonance upward to exactly 60 kHz.

Applying way too much signal to the antenna terminals in order to get 1 Vpp from the LM353 shows the limiter in action:

BP and Xtal filter out – 10.0 v sine 10 Meg xfmr

The resonator sees no more than 200 mV in either direction from the bias level, so it’s all good.

On the low end, the diodes have no effect:

BP and Xtal filter out – 1.1 v sine 10 Meg xfmr

Pay no attention to all that noise.

My first thought was to put the diodes across the resonator, a Bad Idea: straight up, doesn’t work. The 1N5819 datasheet shows they have about 300 pF of junction capacitance at zero bias and a pair of ’em will swamp the resonator’s internal 0.8 pF parallel capacitance and punch it out of the circuit.

2017-09-25

Tour Easy Headset Wrench

The headset on my Tour Easy ‘bent worked its way loose, which led to a disturbing discovery: the headset wrench I made from a discarded flat wrench vanished with the shop tools donated to MakerSmiths.

Fortunately, we live in the future:

Tour Easy Headset Wrench - Slic3r preview — Tour Easy Headset Wrench – Slic3r preview

A thin plastic wrench is absolutely no good for torquing down the locknut, but that’s not what it’s for. Adjust the bearing race to the proper preload with this wrench, hold it in place, then torque the locknut with the BFW.

The OpenSCAD source code as a GitHub Gist:

	// Tour Easy Headset Wrench
	// Ed Nisley KE4ZNU – September 2017

	/* [Extrusion] */

	ThreadThick = 0.25; // [0.20, 0.25]
	ThreadWidth = 0.40; // [0.40]

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	Protrusion = 0.01; // [0.01, 0.1]

	HoleWindage = 0.2;

	//- Sizes
	/* [Dimensions] */

	WrenchSize = 32.0; // headset race across-the-flats size
	NumFlats = 8;

	JawWidth = 10.0;

	JawOD = 2*JawWidth + WrenchSize;
	echo(str("Jaw OD: ",JawOD));

	StemOD = 23.0;

	WrenchThick = 5.0;

	HandleLength = 2*JawOD;
	HandleWidth = 25.0;

	//- Build things

	difference() {
	linear_extrude(height=WrenchThick,convexity=4) {
	hull() { // taper wrench body to handle
	circle(d=JawOD);
	translate([0.75*JawOD,0,0])
	circle(d=HandleWidth);
	}
	hull() { // handle
	translate([0.75*JawOD,0,0])
	circle(d=HandleWidth);
	translate([HandleLength,0,0])
	circle(d=HandleWidth);
	}
	}
	translate([0,0,-Protrusion])
	rotate(1*180/NumFlats) { // cosine converts across-flats to circle dia
	cylinder(d=WrenchSize/cos(180/NumFlats),h=(WrenchThick + 2*Protrusion),$fn=NumFlats);
	}
	translate([-StemOD,0,WrenchThick/2])
	cube([2StemOD,StemOD,(WrenchThick + 2Protrusion)],center=true);

	translate([WrenchSize,0,WrenchThick – 3*ThreadThick])
	linear_extrude(3*ThreadThick + Protrusion,convexity=10)
	text(text=str("TE Headset"),size=8,spacing=1.20,font="Arial",halign="left",valign="center");
	}

view raw Tour Easy Headset Wrench.scad hosted with ❤ by GitHub

Now, I’d like to say that was easy, but in actual point of fact …

First, I forgot to divide by cos(180/6) to convert the across-the-flats size to the diameter of OpenSCAD’s circumscribed hexagon-as-circle, which made the wrench uselessly small:

Tour Easy Headset Wrench - v1 — Tour Easy Headset Wrench – v1

If you have a 28 mm nut with low torque requirements, though, I’ve got your back.

While I had the hood up, I slenderized the handle into a much shapelier figure:

Trotting off to the garage with a warm plastic wrench in hand, I discovered the blindingly obvious fact that the headset nuts have eight sides. On the upside, the number of sides became a parameter, so, should you happen to need a five-sided wrench (perhaps on Mars), you can have one.

So, yeah, it’s rapid prototyping in full effect:

Remember, kids, never design while distracted …

2017-09-21

American Standard Kitchen Faucet: Cleaning and O-Rings

The O-rings on the spout of our American Standard kitchen faucet wore out again; having described that repair many times, there’s no need to say much more about it. I didn’t want to get into this repair while thinking about the hot limit problem, but I did check to make sure the box under the sink had some O-ring replacement kits.

A bench vise with soft jaws holds the spout while you remove the escutcheon ring retainer:

Kitchen faucet spout – in vise

Basically, just tap around the ring with a long drift punch and it’ll eventually fall out onto the reasonably clean rag below it.

The interior of the spout before cleaning shows why you should never look into your plumbing:

Kitchen faucet spout interior – before

After a few hours in a white vinegar bath and a few minutes of scrubbing with a ScotchBrite pad:

Kitchen faucet spout interior – after – 1

Another view:

Kitchen faucet spout interior – after – 2

Obviously, you could do better, but it’s hard to get excited about the last few nodules. For whatever it’s worth, the nodules grow despite our water softener; I have no clue what’s going on in there.

A few wipes of silicone grease, reassemble in reverse order, apply a firm shove, and it’s leakless again. For a while, anyhow.

2017-09-16
LF Crystal Tester: Variable CX
Replacing the 22 pF series capacitor with a variable cap went smoothly after I got over having to rip-and-replace the adjacent socket and header, too:

LF Crystal Tester – variable CX

The circuit remains the same, plus a test point to simplify measuring the actual capacitance:

Test Fixture – variable CX

I didn’t add a jumper to disconnect the crystal fixture, because (I think) it would add too much uncontrolled stray capacitance: removing the header would disconnect the socket / header wires.

The little red cap adjusts from (nominally) 3 pF to 28 pF over half a turn, without a stop. The rotor does have a marked side, but basically you’re supposed to tune for best picture and leave it at that.

The AADE L/C meter works fine, but in the low pF range everything affects the reading. The only way to measure the actual capacitance seems to be:
- Clip one lead to the top of the 24 Ω terminating resistor
- Hold the other within a millimeter of the test point pin
- Zero the meter, note any residual offset
- Touch clip lead to test pin
- Note reading, mentally subtract residual offset
The as-installed range spans 6.5 pF to 28 pF. I think I can measure it to within ±0.05 pF, with a considerable dependence on maintaining the same pressure on the clip lead.

I suppose if you were doing this for real, you’d throw another Teledyne relay at the problem.
2017-09-08