Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
While setting up a Raspberry Pi camera, I had occasion to pull out its USB power cable, whereupon grabbing the camera while unscrewing it from the tripod felt unusually sharp:
Micro-B USB – RPi jack
It seems the wall wart’s USB Micro-B connector pulled apart:
Micro-B USB connector – disembowled
Somewhat to my surprise, it was a CanaKit 5 V 2.5 A wall wart, definitely not the cheapest piece of junk ever made by the hand of man. On the other paw, it’s been around for quite a while, so …
Even I will agree that’s not a repairable failure, so I planned to splice in a Micro-B connector from a volunteer chosen from the Box o’ USB Micro-B Cables:
Each of those conductors appears to be made up of nine springy copper-colored 0.06 mm strands, somewhat smaller than 40 AWG: not what you want on the business end of a 2.5 A wall wart. I had previously measured the cable’s overall resistance with a surprisingly useful Treedix USB Cable Tester and it was on the very high end of the charge-only cable collection.
So I soldered a female USB-A breakout from the Drawer o’ USB Breakouts to the wall wart’s wires, snapped a 3D printed case around it, got a good (0.26 Ω) A-to-Micro-B cable from the Box o’ USB Adapters, and moved on.
Our ancient Branson 200 Ultrasonic Cleaner began behaving erratically due to water seeping under the rather casual seal from last year’s fix. Although drying the switches let it start up again, it would run for only a few seconds before shutting down again, which suggested a deeper problem than just the switches.
Take a picture of the PCB’s component side:
Branson 200 Ultrasonic Cleaner – PCB component side
And of the solder side:
Branson 200 Ultrasonic Cleaner – PCB solder side
Transform those pictures to be the nice real rectangles shown above, resize to a common pixel format, mirror the solder side, turn it into a layer atop the component side, then tweak its opacity to make both sides visible at once:
Branson 200 Ultrasonic Cleaner – PCB overlay
Some pondering produces a partial schematic of the left half of the board:
The 1:1 transformer is constantly powered, so the ON button connects the 120 V (!) half-wave rectified output to the +12V supply bus, with the 750 Ω resistor dropping most of the voltage while the switch is pressed.
The hotwired +12V supply forces the relay closed, which (in some as-yet unidentified way) fires up a +12V power source to hold the relay closed, with the 555 timer driving an MC14060 14-bit divider to count down the time until it turns itself off.
Reminder: this design dates back to the days when a pair of chips and a handful of through-hole components cost less than one of those fancy microcontroller thingies.
Plug the cleaner into an isolation transformer and trace the half-wave rectified signal through ON button to find it got all the way to the contact on the end of the orange wire in the connector, but did not reach the pin header on the PCB.
A closer look at the connector revealed a broken contact on the white wire, which I (rather crudely) soldered together while considering my choices:
Branson 200 Ultrasonic Cleaner – soldered contact
While plugging that wire back in place, this happened:
Branson 200 Ultrasonic Cleaner – another broken contact
Neither of those are the (presumably) similarly failed orange wire, but even I can get a clue from three similar failures.
So I replaced the OEM connector with a JST-XHP 2.54 mm connector from an assortment I got for another project, replaced the chunky 22 AWG wires with flexy 26 AWG silicone wires in the same cheerful rainbow colors, and it began working perfectly again.
The buttons needed another water seal, so I tweaked the previous layout to kiss-cut GITD tape and through-cut colorful vinyl sheets:
Branson 200 Ultrasonic Cleaner – power button cutting
Capped with a transparent cover sheet cut from a pack of PDA screen protectors (remember PDAs?):
Branson 200 Ultrasonic Cleaner – power button cover
In truth, the GITD tape is too thick, so I’ll probably repeat this dance later this year.
FWIW, I was totally ready to buy a new ultrasonic cleaner, but all of them have scathing one-star Amazon reviews, to the extent I decided fixing this cleaner would be much easier than fixing a new one that’s been cheapnified to the point of no return. A common complaint seems to be water leaking into their capacitive switches and killing the circuitry stone cold dead: not an improvement over this one.
Work Sharp Precision Sharpener – Blade Clamp operation
What’s not obvious is that the socket can rotate only 180°, which means you (well, I) must remember which way to turn it based on the presence or absence of the small white mark. I get it wrong somewhat more than half the time while sharpening a small symmetric blade, rather than a knife with a handle, so I added arrows to the socket.
With the white mark upward, turn 180° counterclockwise:
Under the plausible assumption the security / surveillance cameras along the Walkway Over the Hudson aren’t the cheapest junk available from a randomly named Amazon seller, this came as a surprise during a recent Walkway At Night stroll:
Walkway Over the Hudson – camera LEDs
The IR LEDs emit just enough red light to be dimly visible to the human eye, but appear much brighter to a silicon detector. I think the long gap at the bottom right is a sensor of some sort, so the array of 18 LEDs has two deaders, one near death, and six more fading away.
It’s a W5W “parking light” in the same fixture as the melty halogen high-beam bulbs (used as daytime running lights at half power), so it gets toasted on those occasions when we drive somewhere.
The adhesive holding the LED strip to the aluminum shell fossilized and came loose:
White W5W Parking Light – failed adhesive
Now that I know what to look for, I’d get LED bulbs with chips soldered directly to the PCB, although it’s not obvious what holds the PCB to the aluminum frame.
Having recently filed our income taxes, this email came as a mild surprise:
IRS Audit email
The From field seemed a bit sketchy, but, hey, maybe the IRS subcontracted their email vendor after having lost much of their staff in the name of efficiency.
The hidden part of all three LED arrays in the dead garage light looked like this:
LED Garage Light – inadequate heatsink compound
Although the compound was still gooey, there wasn’t nearly enough of it. The few tendrils on the heatsink suggest the LED array had bowed upward, pulled away from the cast aluminum, and eliminated any direct conduction.
A bit of probing showed each LED array had 16 series groups of 4 parallel LEDS, with one group in each array failed open. That group was toward the end away from the inadequate heatsink compound: the LEDs died from heatstroke brought on by neglect.
The Drawer o’ LED Arrays disgorged a bag of surplus LEDs labeled “10 W 9-12 V 750 mA”:
LED Garage Light – epoxy replacement
It’s sitting on a generous blob of steel-filled JB Kwik epoxy that should do a great job of conducting heat. A bag of cheap constant-current supplies is on order.
Amazon has similar “10 W 9-12 V 350-450 mA” arrays.
Try as I might, I can’t get 10 W from those numbers, but I’ve never understood advertising math.
The Smell of Molten Projects in the Morning 