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

OttLite LED Conversion
Although Mary liked the illumination from her OttLite (an old 13 W fluorescent Folding Task Lamp), neither of us liked its tiny base and tippy nature. It recently fell / was dropped / jumped to its doom, smashing the CFL tube and wreaking havoc on the tiny plastic studs holding its large cast-iron weight and steel base in position. Given that the CFL ballast had started humming a while ago, I took it apart to see whether I could salvage anything from the rubble.

Remove:
- Four screws under the fuzzy felt feet
- One screw under the label on the back
- A final screw that becomes visible only after disemboweling the hinge assembly by unscrewing the obvious endcaps:
OttLite LED Conversion – hinge screw

Pull the hinge end of the white inside panel away from the outer stand at enough of an angle to disengage all three latches holding it to the base, then remove it just enough to let you start cutting wires around the ballast…

I rebuilt the thing with a pair of 24 V 150 mA warm-white LED panels (good industrial surplus, not the usual cheap eBay crap) powered by a 19 V laptop adapter (from IBM, no less) through a (cheap eBay) boost converter sticky-foam-taped where the fluorescent ballast used to live:

OttLite LED Conversion – boost supply wiring

The power supply had only two conductors, the central wire surrounded by twisted shielding, and didn’t require a fussy interface. Hooray for simple bulk power supplies; I lopped off the connector and soldered the wires directly to the boost converter.

The original lamp wiring has a 120 VAC switch inside the hinge that turned the lamp on as you raise the arm holding the CFL tube: exactly what I need for its new use. That eliminated figuring out how to crack the arm apart to rewire it.

I harvested the base from a(nother) defunct CFL bulb:

OttLite LED Conversion – harvested CFL base

By soldering wires directly into the pins, I could reuse the existing CFL socket in the lamp arm, the existing wiring, and the switch.

The LED panels dissipate 3-ish W each:

OttLite LED Conversion – LED panel layout

They’re mounted on a 0.1 inch aluminum sheet from the heap that required exactly one saw cut to fit into the space available, so I defined it to be perfect. The 4-40 screws holding the panels in place continue through the plate and 3/8 inch aluminum standoffs into a quartet of knurled inserts epoxied into eyeballometrically match-drilled holes in the lamp arm:

OttLite LED Conversion – epoxied threaded inserts

The faint yellowish discoloration from the CFL tube’s heat and UV is much more visible in real life, but nobody will ever see it again. The scrawled blue (+) and (-) marks give the socket polarity; it’s not mechanically polarized and a bit of care is in order. The black rectangle is actually a shiny metal sheet intended to reflect heat from the CFL tube’s base away from the plastic arm.

I set the boost converter to 23.5 V, at which point the LED panels draw about 100 mA each and get just over uncomfortably warm after an hour or two:

OttLite LED Conversion – in action

The panels run 120 °F = 50 °C and the SMD LEDs probably exceed 150 °F = 65 °C. The scant surplus doc touted “No heatsink required” and the single-sided FR4 PCB insulates the LEDs from the aluminum sheet, but I still smeared some heatsink compound behind the panels in the hopes of spreading the heat out a bit.

I glued the shattered base studs back in place with IPS #3, surrounded them with generous epoxy fillets, plunked the cast iron weight in place atop some waxed paper to mold the epoxy to fit (and let me remove it again, if needs be), screwed everything together, and stuck a foam sheet over the steel base plate. It’s as tippy as before, but at least the LEDs won’t shatter if when it falls. It really needs a larger base; a polycarbonate plate might work, if only I could figure out how to attach it.

All in all, the lamp looks good and the warm-white LEDs with DC drive don’t produce that horrible fluorescent flicker.

The lamp now sports a label identifying it as a NisLite; because P-Touch labeler.
2016-03-17
Tour Easy: Long-Deferred Drivetrain Maintenance

A few months back, the 13-tooth sprocket on my Tour Easy started skipping, which reminded me that I planned to replace all the drivetrain components. Time passed, the winter remained unseasonably warm and sunny, we kept riding, the skipping got much worse, and I just shifted across that sprocket.

Finally, the rains returned, I heaved the bike up on the workstand, and started replacing things. Judging from the accumulated crud and severe wear, it’s been on there for quite a while:

Sprocket with broken teeth – as found

Here’s the offending 13-tooth sprocket, all shined up;

Sprocket with broken teeth – detail

I don’t recall a catastrophic failure that stripped all those teeth off in one shot. A closer look showed cracks in the few remaining teeth:

Sprocket with broken teeth – cracked teeth

Which explains why the skipping gradually got worse: the poor sprocket shed teeth as I rode blithely along.

Huh.

That’s what happens with a severely worn sprocket: the chain applies tension to just the topmost tooth, rather than distributing it on the teeth around a third (or more) of the sprocket, and, one by one, that force breaks the teeth. The top picture shows at least one other sprocket with a missing tooth; all display the shark-fin profile of heavy wear.

As you can tell from the other bike pix & repairs around here, I’d rather ride than mess around with cleaning and suchlike. We’re on our second set of drivetrain components in 15 years, so I’d say treating all that stuff as consumable seems a fair tradeoff…

2016-03-16
Vacuum Tube LEDs: Knockoff Neopixel Failure
The knockoff Neopixel epoxied atop the big incandescent bulb just failed:

Vacuum Tube LEDs – ersatz heatsink plate cap

It stopped changing colors and began blinking high-intensity bursts of the RGB LEDs. Which was interesting, I’ll grant you, but didn’t produce the desired, ah, mood.

Differential diagnosis:
- Reboot that sucker: fail
- Shot of circuit cooler: fail
- Failing LED with known-good Arduino Pro Mini: fail
- “Failing” Arduino Pro Mini with known-good LED: work
Looks like a permanent WS2812B controller failure this time around.

It’s been plugged into a Kill-a-Watt meter that reports it ran for 415 hours and used 150 W·h of energy, for an average 360 mW dissipation. I think the actual power falls well below the meter’s lower limit, so I doubt the accuracy, but it’s a whole bunch less than a nightlight and much more interesting.

Now, to break that epoxy bond without breaking the bulb …
2016-03-10
Adaptek AVA-2902E/I SCSI Card: Low Profile Bracket Hack

I picked up an Adaptek AVA-2902 SCSI card from eBay to use with an ancient Epson Perfection 636 SCSI scanner from the heap, but it came with a high-profile bracket wrapped around its DB-25 connector:

SCSI card bracket fix – before

The old-school serial port card sitting atop it (from one of the off-lease Optiplexes in the stable) has a low-profile bracket that seemed promising, so I swapped the brackets.

Alas, the SCSI card positioned the DB-25 just a smidge higher than the serial card, putting the right-angle top of the bracket about 2 mm above the ledge, where it prevented the locking cover from engaging. I filed the bracket’s DB-25 mounting holes into ovals, using up all the slop around the connector shell, to no avail.

So I snipped off most of the bracket’s top, grabbed it in the bench vise, smashed the corner with a drift punch, and bashed the whole affair 2 mm lower. It fit reasonably well, although there’s an air gap near the bottom of the bracket where it tapers down to the guide slot. The SCSI connector barely fit, with some persuasion, under the locking cover:

SCSI card bracket fix – installed

Close enough for me; the scanner (looming over the SCSI connector) works fine and delivers much better image quality / color balance than the crappy HP 7400C with an auto-feeder that I’d been using.

SCSI cables look like gas pipes in this day & age of tiny USB cables and teensy HDMI connectors…

2016-02-29
Kenmore Model 158: Older Foot Pedal Resistor

Based on the paperwork tucked into the sewing table, the most recent Kenmore Model 158 sewing machine in our stable dates to 1972, a bit earlier than the others, and has a metal-cased foot pedal with a wire-wound resistor:

Kenmore Model 158 – new-ish foot pedal resistor

The cord insulation stiffened up over the decades and I wanted to replace it, but the contacts in the sewing machine connector were spot-welded to the conductors with no room for teeny screws:

Kenmore Model 158 – new-ish foot pedal connector

I blew out the fuzz, put it back together, and it works pretty well, modulo the usual low torque at slow speeds issue.

The discrete resistor taps produce a somewhat stepped response, but early reports suggest it’s not enough to be annoying; it’s much more stable than the carbon disks in the more recent pedals.

2016-02-27
LED Shoplight Conversion: Fluorescent Fixture Teardown

The weakest fluorescent shop light fixtures always fail during cold weather (apart from the usual early tube failures) and this winter’s cold spells triggered the usual carnage, so I picked up half a dozen (cheap) 22 W LED T8 tubes and set about rewiring three defunct (cheap) fluorescent fixtures from the recycle heap. The new LED tubes run directly from the AC line; you must remove the fluorescent fixture’s ballasts / capacitors / starters and rewire the “tombstone” lampholders accordingly.

The first challenge, as always, involved taking the fixtures apart. Turns out prying the endcap away from the fixture enough to clear the pair of bumps punched into the metal does the trick:

Fluorescent Shoplights – endcap latches

Each endcap contains the ballast inductor / choke and power-factor correction capacitor for one tube. The inductors from one shoplight had a fancy plastic tab that might have held the capacitor in place, but that’s about the only difference:

Fluorescent Shoplights – ballasts

The 150 kΩ resistor has its leads twisted around the capacitor leads without benefit of that fancy solder stuff one might think necessary for a good connection.

The capacitor contacts use the minimum possible amount of material:

Fluorescent Shoplights – capacitor termination

I think the caps use metallized Mylar film, but who knows?

The inductors measure 280 mH and the caps a whopping 5 µF. I might trust the inductors in a low-voltage circuit, but the caps have no redeeming features and went directly to the trash.

The starter PCB lived in the center of the fixture:

Fluorescent Shoplights – starter circuit

I deliberately picked LED tubes with the AC line contact on one end and the neutral contact on the other, so as to not put line and neutral contacts in the same tombstone. After rewiring, the neutral endcap looks like this:

Fluorescent Shoplights – neutral endcap

The other endcap holds the power cord and has a green earth ground wire snaking out to a little tab passed into a slot punched in the metal case. I replaced the tab with an actual screw / solderless connector / toothed washer, but have no pix to show for it.

The LED tubes run at 6500 K and contrast harshly with the warm-white tubes in the fluorescent shoplights. I went with the highest light output, because even the best (cheap) LED tubes produce barely half the output of the fluorescents: 2000-ish lumens vs 3900-ish.

2016-02-26
Sears Sewing Table: Sewing Machine Supports

For reasons that should not require explanation by now, Mary just acquired a large sewing table (along with a Sears Kenmore Model 158 sewing machine that’s slightly older and fancier than the three we already have). The table has an opening fitted to the machine base, but the rubber pads atop the leveling screws had long since stiffened up and two screws were frozen in place. A few drops of penetrating oil released the screws and, mirable dictu, they have ordinary 6-32 threads.

Some rummaging turned up four PC case screws and soft caps intended for wire shelves, which easily combined into replacement machine supports:

Sewing Machine Supports – inserting screws

Once again, I’m using the drill press as a low-force arbor press, with a chunk of aluminum tubing to shove the screw flange into the slightly smaller plastic cap.

Spun into their brackets, they look quite nice, not that anybody will ever see them:

Sewing Machine Supports – installed

The new-to-us table replaces the incredible collection of junk previously supporting Machine #3. I tucked some plastic foam around the near and right edges to fill the small gaps and it fits well:

Sewing Machine Supports – machine installed

Obviously, the foam will fall out whenever Mary lifts the machine to tinker with machinery under the platform, so we’ll see how often pins & needles slip through the cracks without the foam.

That machine awaits a lighting update, because I’m awaiting some rectangular chip-on-board LED strips from halfway around the planet.

Early reports concerning the sewing table seem promising…

2016-02-24