Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Before trotting off to college, my Shop Assistant repaired a pair of headphones she’d scrounged at the end of her Senior year; they were nice Skullcandy on-ear phones with one dead cup. The previous owner evidently wasn’t into fixing things and bequeathed them to her.
She dismantled the offending cup to find some really grody soldering that ought to have produced a cold solder joint: the common lead wasn’t making contact with the plug. Alas, the only way to proceed was to slice the injection-molded cover off the plug and see what was inside; to our surprise, everything looked fine.
We then cut an inch off the cable and pulled the conductors out:
Broken headphone cable conductors
Well, that was easy! Here’s a closer look:
Broken headphone conductor – detail
The three broken wires (only one of which was completely disconnected) failed exactly at the end of that plug covering. It had strain relief notches, but we guessed the previous owner had no qualms about bending the cable hard against the end of the plug.
She soldered it up, shrank some heat stink tubing around the plug and its sliced cover, wrapped self-vulcanizing tape around the junction for better strain relief, and it’s all good. She’ll get plenty of use out of the headphones in the dorm …
I’d waited for a few days for the silicone to cure, then put the clamps back in their home. When I went to use them, the pads were firmly affixed to the plate. Evidently, the copper-loaded silicone gasket compound takes a few days longer than forever to cure, which is not what I gathered from reading the label.
It may well be that adhesive has aged out, because when I went to try it again, the first half-inch inside the tube had turned into solid gum. Yes, it cures inside the tube and not outside.
Other than that, it seems like good stuff; I may pick up another tube and give it a second chance. Who knows? It might be useful in a plastic extruder or something like that.
As described there, the buttons on the back of my pocket camera stopped working, but the obvious laying-on-of-hands repair (i.e., wiggling the cables) didn’t improve things. I later discovered out that two other buttons on the side that didn’t go through the same flex cable were also dead, which suggested that the common failure was on the CPU board deep inside the camera. I gave it to my Shop Assistant with some handwaving about how she could maybe fix it by delving deep inside, tracing the cables, and doing some jiggling: if she could fix it, she could have it.
The first step was to take both covers off, which required a Philips 00 bit:
EX-Z850 front cover removed
Then the side plate comes off, which requires maneuvering the spring-loaded battery latch out of its recess, at which point the lug for the carry strap will fall out:
EX-Z850 battery latch and carrying lug
En passant, we discovered why the clock dies while changing the battery pack. It seems the miniature rechargeable lithium (?) NiMH (?) cell has rotted out:
EX-Z850 internal battery corrosion
Fortunately, it charges in a cradle, so the main battery can remain in place indefinitely. We’ll replace that thing at some point.
The CPU board has two flex cable connectors on the front surface and two on the back. My Shop Assistant released the clamps, removed the cables, wiped down the contacts with DeoxIT Red, gave it a test run with the covers off, and came bounding up the stairs as happy as I’ve ever seen her: the camera worked perfectly again!
Not being used to these things, though, she managed to crack one of the side latches on the far connector. I’ll admit to doing exactly the same thing, so I knew how to fix it: a dab of acrylic adhesive holds the fragment in place with a bit of springiness to hold the latch down.
EX-Z850 connector repair
The connector in question comes from the flash control board, to which those other two buttons (Ex and Drive mode) connect. The inside of the camera is a maze of connections, so I guess that was the simplest way to get the conductors through the body.
She reassembled the camera and it continued to work; we declared the job a complete success.
Shortly after that, I promoted her from Shop Assistant to Larval Engineer, First Instar, and we installed her in her new socket at college, where that camera should come in handy for something.
I think she’ll ace the Freshman Engineering Practicum, wherein her compadres will learn how to solder components to circuit boards, use multimeters & oscilloscopes & other instruments, and generally survive in a laboratory. Maybe she can wrangle a job as a Lab Assistant?
Before trashing (*) all those caps from the Ampeg, I marched them past a capacitance meter that gives the dissipation factor D. As D = tan δ = ESR / ¦X¦, we know ESR = D*¦X¦ at the meter’s 1 kHz test frequency. We don’t know the magnitude of the total reactance X (the meter doesn’t tell us that) and in this case we can’t assume the ESR will be small with respect to the capacitive reactance Xc = 1/2πfC.
Ampeg capacitors
The smaller green 0.022 µF Cornell-Dubilier caps all came in with D=0.05, so they’re marginal.
The larger green 0.15 µF Cornell-Dubilier caps had D=0.00 and the black 0.1 µF was D=0.01. Those are OK.
The small black caps had D=0.14. Yikes! The larger one and the yellow cap had D= 0.01 or 0.02.
The blue Ducati (!) electrolytics ranged from 0.06 to 0.48. That was without reforming, as the last time Phil turned it on, the finals about melted down: I wasn’t going to risk that again just to find out if you can reform all the electrolytic caps without the tubes in place.
So, yeah, some of the coupling caps were exceedingly bad. If you’d like to rub the values & data against the schematic to find out which one(s) were killing the finals, go ahead.
All of the measured capacitance values were within spitting distance of their nominal values.
[Update: Eks points out that I really should measure the leakage at operating voltage, so as to find the current that would drive the grids off their normal bias points. That’s a project for another day… ]
(*) They’re in the e-waste recycling box, of course.
So the hydration pack I’ve been using for a few years started piddling all over the floor, whereupon some debugging revealed a pinhole leak where the large thermally sealed flange meets the bag side. Nothing, but nothing adheres to the polyethylene (or some such) bag material, but a blob of acrylic caulk (armored with a layer of electrical tape, not shown) may suffice for a while.
Hydration pack leak repair blob
I did the same thing to the other side as a prophylactic measure…
Got a stepper motor from halfway around the planet from the usual eBay source, intended for a direct-drive extruder (at some point). This one has integral wire leads, which is fine with me, but the opening in the rear endcap reveals a bit more of the innards than one usually sees:
ACT 17HS5425 stepper – exposed winding
Yup, that’s one winding peeking out. Although the wire insulation should take care of anything conductive, I’d expect the same casual attention to detail in the winding terminals.
I’d worry more if this were being used in a metal-cutting operation, but a snippet of heatshrink tubing and a blob of hot-melt glue seem in order.
For what it’s worth, the motor is an ACT 17HS5425:
1.8°/step
48 mm case length
3.1 V
2.5 A
1.25 Ω
1.8 mH
48 oz·in holding torque
2.8 oz·in detent torque
68 oz·in rotor torque
No torque curves and nothing more in the way of a datasheet.
The Smell of Molten Projects in the Morning 