Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The basement came with several LED bulbs screwed into old-school ceramic sockets with pull-chain switches. This adapter had an LED bulb in its socket and another LED fixture plugged into an outlet:
Lamp socket adapter – failed weld
The fixture began flickering some days ago, which I attributed to a problem with its power supply. When both the bulb and the fixture went dark, I had enough of a clue to locate the real cause.
The scorched plastic near the discolored weld nugget on the threaded shell suggests something ran overly hot in there for a while.
Peeling the aluminum shell off reveals the problem:
Lamp socket adapter – detail
Looks to me like the weld started out weak and gradually fell apart as the socket heated / cooled in use, with increasing resistance producing more heat every time.
The LED lamp + fixture added up to 100 W, so about 1 A is all it takes.
The venerable (circa 1993) Whirlpool clothes dryer (LER443AQ0) that Came With The House™ failed in action: the drum occasionally stopped turning (and, fortunately, heating) while the control timer continued ticking along. The symptoms suggested one of the many thermal switches / thermostats / fuses was bad, but because the problem was intermittent, the only practical alternative was replacing all the things.
Which, it turns out, costs about ten bucks from the usual source. I remain unconvinced paying an order of magnitude more for what look to be identical parts will, in fact, bring either different parts or higher quality.
The wiring diagram, which I consulted only after the fact, shows it was most likely the “Not Resettable” Thermal Fuse in series with the drum motor, because the other contestants are in series with the heater and the Operating Thermostat would trip when the blower stopped blowing:
Whirlpool dryer – wiring diagram – detail
The fact that the Thermal Fuse should not “reset” after it trips seems worrisome, but failures are like that.
All those parts are accessible only through the rear cover, but you should definitely vacuum out as much fuzz as possible before popping the cover (with vacuum in hand):
Whirlpool dryer – heater duct top
Of course, all the old parts show fine continuity, because intermittent:
Whirlpool dryer – thermal switches
With the new parts in place, the dryer has chugged through half a dozen loads without incident: so all’s well that ends well.
Six years ago I replaced the W5W incandescent front side marker bulbs in our 2015 Subaru Forester with amber LED bulbs:
Side Marker bulbs – failed adhesive
The adhesive holding the LED PCB to the aluminum “heatsink” has fossilized and the strip on the right is peeling off (with the left one not far behind), which likely accounted for its loss of light output and flickering.
Tearing it apart reveals the LED layout and what looks like a bridge rectifier or a big resistor (to fool the CAN bus?) on a tiny PCB jammed inside the shell:
Side Marker bulbs – rectifier
The other side of the PCB could be a buck converter:
Side Marker bulbs – buck converter
In round numbers, we’ve driven 18000 miles at an average of maybe 40 mph over those years; call it 450 hours. However, the side marker lights aren’t on unless the headlights are on; we do very little night driving, which means those LED bulbs are the usual crap.
The switch on the Anker LC-40 flashlight serving as a running light on my Tour Easy became slightly intermittent before I replaced it with a 1 W amber LED, but it was still good enough to become the troubleshooting flashlight in the tray next to the Prusa Mk 4 printer. Eventually, of course, it failed completely and Something Had To Be Done.
Although I knew an exact replacement switch had to be available from the usual sources, I could not come up with a set of keywords capable of pulling them out of the chaff.
Which turned into a multi-dimensional search over cap geometry, TPU extrusion speeds & feeds, and various impossible-to-directly-measure sizes:
Anker LC-40 Flashlight – TPU cap iterations
The squarish block over on the left is PrusaSlicer’s version of a support structure wrapped around the first cap version; if human lives depended on it, I could surely extract the cap, but it would take a while.
The remaining debris samples occured while discovering:
An extruder temperature of 230 °C, not 250 °C, works well
A conical shape of the lip around the open end to eliminate the support structure
TPU doesn’t bridge well, so the closed end must be down
Length of the central pillar to barely touch the switch stem when released
Cap length and wall thickness so the TPU shell can collapse enough to actuate and release the switch stem
Because I expected this would be an easy job, I used snap ring pliers to unscrew and rescrew the threaded retaining ring holding the switch PCB in place. Because the pliers didn’t have a stable grip on the ring, the threads eventually became just a bit goobered.
This was not a problem, because I have a(nother) 3D printer:
Anker LC-40 Flashlight Retainer – show view
The gray thing on the right is a simple pin wrench fitting both the original and the replacement retaining rings, so I can orient the rings properly while unscrewing & rescrewing:
Anker LC-40 Flashlight – pin wrench in place
The threads have a 0.75 mm pitch and, while it’s possible to print screw threads, even a tedious 0.1 mm layer height would define each turn of the thread with only 7-½ layers.
This was not a problem, because I have a mini-lathe:
Anker LC-40 Flashlight – thread cutting
The yellow & green things on the left of those solid models are the fixture holding a retaining ring for threading and the washer applying pressure to keep the ring in place:
Anker LC-40 Flashlight – lathe fixture – detail
The alert reader will note that washer lacks holes for the alignment pins I added after seeing the washer sit not quite concentric on the fixture. I could call it continuous product improvement, although I doubt I’ll print another one.
Setting up the lathe involved finding the proper set of change gears, including the vital 42-50 stacked gear I made a while ago to print metric threads on a hard-inch lathe:
Anker LC-40 Flashlight – lathe change gear train
Although you’re supposed to measure the thread spacing on a skim pass, I find it’s easier to just measure the carriage movement for one spindle rotation:
Anker LC-40 Flashlight – lathe gear check
A few passes produced a fine retaining ring:
Anker LC-40 Flashlight – OEM vs lathe-cut threads
Sporting much nicer looking threads than the goobered original:
Anker LC-40 Flashlight – OEM vs lathe-cut threads
The original switch had a stabilizing ring around the body to prevent it from wobbling under the original rubber cap.
This was not a problem, because I have a laser cutter:
Anker LC-40 Flashlight – new switch in stabilizer
Those came from a scrap of fluorescent acrylic.
The wave washer behind the acrylic stabilizer improves the contact between the PCB trace around the rim and the flashlight tailcap, with the current passing through the body to the “light engine” up front. The retaining ring provides enough pressure to compress the wave washer, which is why it’s so easily goobered without a close-fitting pin wrench.
With everything assembled in reverse order, the flashlight worked pretty much as it did back when it was new:
Anker LC-40 Flashlight – TPU cap installed
However, after describing this during a recent SquidWrench meeting, I discovered that adding “latching” to my keywords surfaced a bodacious assortment of flashlight switches, so (a few days later) I removed the not-quite-right switch and replaced it with an identical twin of the OEM switch requiring just a little lead forming to fit the PCB.
Even better, using the 3D printed pin wrench to screw the original retaining ring into the flashlight’s aluminum threads a few times re-formed (unrelated to recent electrolytic capacitor reforming) its goobered threads well enough to fit and work perfectly again.
So I have:
… reassembled the flashlight with more-or-less original components
… a repair tool kit ready when another LC-40 fails
… re-learned the lesson that any time spent making a fixture or a special tool is not deducted from one’s allotment
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Yes, it’s built into a recycled modem case. No, they don’t make modems like they used to, either. Regrettably, the five status indicators on the left were not set up as Der Blinkenlichten.
The inside view:
S-100 Bus Cap Reforming – inside view
The multi-winding transformer in the back feeds bridge rectifiers (out of sight behind the caps) producing bulk DC:
S-100 Bus Cap Reforming – bulk supply caps
The gray cap is 52 mF = 52000 µF 15 V for the +5 V regulators supplying the TTL logic on each board.
Two of the three blue caps (each 9 mF = 9000 µF 50 V) are for the +12 V and -12 V supplies. I think the third cap is a separate supply for a different purpose, but I did not trace out the wiring.
The on-board regulators seem to use solid electrolyte caps that should still be in fine shape you should replace on principle, per ericlscott’s experience. You’d want to bring up each board separately while probing the voltages; the box of stuff accompanying the system has an extender card that should make probing easier.
I hoped to boot the thing after restoring the caps, but a casual inspection showed wire corrosion:
S-100 Bus backplane – jumper wire corrosion
You’d want to pull the backplane out and replace those jumpers, as well as clean the bus contacts, before applying power.
The system has two 8 inch floppy drives in a separate case with its own power supply:
S-100 Bus floppy drives – overview
There was some corrosion in there, too:
S-100 Bus Floppy Drive – optical sensor corrosion
So I confined myself to reforming the caps and must let someone with more powerful motivation restore the rest of the system before trying to connect everything and booting CP/M.
The general idea behind “reforming” an electrolytic capacitor is to regrow the oxide layer separating the anode and cathode electrodes, which involves passing a current of about 1 mA for as long as it takes to bring the terminal voltage up to the cap’s maximum rated voltage:
S-100 Bus Cap Reforming – 52mF 15V
That setup consists of an absurd number of PowerPole adapters putting the meter in series with a fuseholder repurposed to hold resistors to limit the current, with leads eventually ending up on the capacitor:
S-100 Bus Cap Reforming – 52 mF 15 V cap connection
The red dot is the overpressure vent, not a polarity marker.
Apparently the Greek mu symbol wasn’t in the font available for the labels, as all the capacitors use m in its place: that capacitor is 52 mF = 52000 µF.
The white plastic ejection handle belongs on the right end of the CPU board seen in the second picture, which was not plugged into its slot when I opened the case. I snapped the handle in place and plugged the board in just to keep it out of trouble. The case does not have board guide slots along the edges that would let the handle eject the board, but all that was definitely in the nature of fine tuning back then.
I started with +15 V through a 16.9 kΩ resistor and swapped in 3.3 kΩ, 1 kΩ, and 220 Ω resistors as the cap voltage crept upward over the course of two days and eventually settled to a steady state:
S-100 Bus Cap Reforming – 52mF 15V final voltage
After discharging, the cap measured 59.5 mF with a 0.3 Ω ESR, which definitely seemed Good Enough.
I reformed the three 9 mF 50 V caps at the same time by applying 50 V to three resistors captured on their screw terminals, changing the resistors as the voltages rose:
S-100 Bus Cap Reforming – 50 V caps
Those three caps eventually measured (clockwise from upper right):
9.66 mF, 1.0 Ω ESR
9.76 mF, 2.6 Ω ESR
10.46 mF, 3.4 Ω ESR
The ESRs suggest they’re somewhat dried out, but I’d be tempted to run them anyway, because the on-board regulators should knock down the ripple.
All of the reformed caps had leakage currents of a few hundred microamps. They’re not new capacitors and never will be, but they may be Good Enough.
Getting the caps out of the diskette drive power supply required easing the entire supply frame / heatsink out of the case before unscrewing the capacitor clamps:
S-100 Bus Cap Reforming – 16 mF 50V
That one eventually measured 22.1 mF with 0.14 Ω ESR. Its sibling, nominally 38 mF at 15 V, came in at 48.9 mF with 0.95 Ω ESR.
The power supply PCB carries a handful of smaller aluminum electrolytic caps that are impossible to remove without unsoldering all the TO-3 transistor leads coming through the aluminum heatsink / frame, then completely dismantling the power supply:
S-100 Bus floppy drives – power supply PCB
Although I reformed the big caps, I think a better plan would be to replace the whole thing with a contemporary switching supply. AFAICT it has 24 V and 5 V outputs; because we live in the future, dual-output switchers are cheap & readily available.
And then I closed the cases to get them ready for the next part of their adventure …
The new control caps on the HQ Sixteen’s handlebars have three switches apiece:
HQ Sixteen – grip cap installed – left
A six-conductor ribbon cable brings those switch terminal through the handlebars, across the smaller PCBs where the original switches plugged in, and atop the main PCB behind / under the LCD panel where they get wired together:
HQ Sixteen – Control Button switch cable
The gray ribbon cable carries power for the LEDs and returns the original switch signals formerly plugged into one of the four-pin headers on the right PCB. The same PCB is used on the other side and the switches over there plug into the other header.
The central PCB is also used for the rear handlebars, which do not have the smaller PCBs, and those switch cables plug directly into four-pin headers mounted instead of the headers for the gray ribbon cables:
HQ Sixteen – Control Button central PCB
Some probing and doodling produced a diagram of the switch connections:
HQ Sixteen – Control Button Wiring
Working with the handlebars either inverted or flipped left-for-right on the workbench makes this far more confusing than it really should be.
In any event, the bottom diagram shows the connections between the two four-pad header positions on the central PCB and the two six-pin headers for the new switches. I used a 2×6 pin header block to plug in the new switches, connected the pins with soldered Wire-Wrap wire, and used three-wire ribbon cable to the PCB pads.
The general idea was to duplicate the Start-Stop and Needle Up/Down switches on both sides, while maintaining the same relative positions of the Fast / Slow switches. In effect, the two new switches on each side are wired in parallel to the original switch pads on the PCB.
Surprisingly, I got the three-wire ribbon cables from the four-pad headers right on the second try, which involved flipping it over. The top and bottom pads on those headers are connected together, so the three-wire cable can go on either way to reverse the positions of the other two wires.
The Smell of Molten Projects in the Morning 