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

  • Arduino Pro: Securing the Serial Connecor

    Epoxy backfill on Arduino Pro serial connector
    Epoxy backfill on Arduino Pro serial connector

    The surface-mount serial connector on an Arduino Pro board isn’t the most robust of devices; the FTDI USB interface and USB cable can apply far too much torque to those little pins. Even before the situation described yesterday, the pins were getting wobbly.

    The connector shell is a big part of the problem, as it doesn’t mechanically lock the pins in place. Installing and removing the FTDI USB board pushes and pulls the pins against their pads, which means the adhesive bonding the pads must handle all that stress.

    Eventually, the Reset and TX pin pads tore loose from the circuit board. At that point, they have no mechanical stability at all; you can bridge a solder blob from the pin to its trace, but the adhesive holding the copper pad in place has lost all strength.

    The fix is straightforward, if ugly.

    • Repair the pin-to-pad/trace connections with something better than a solder blob. I used small snippets of component leads.
    • Apply denatured alcohol and scrub away all the solder flux around the pads.
    • Apply enough epoxy to the back of the connector to bond it, the pins, and the circuit board into one mechanically stable unit. I worked the epoxy between the pins and slightly under the connector shell with a small screwdriver and toothpick.

    Even with this repair in place, the connector is not particularly robust. It’s much better than it was, so we’ll count it as a win.

    This Arduino Pro has survived several projects, hence the hideous solder blobs here & there. I suppose I should just throw the poor thing away, but … that’s not my nature.

  • Improvised Snowthrower Skid Shoes

    Our snowthrower rests the entire weight of the front end on a pair of skid shoes, which erode against the asphalt driveway. Replacements cost nigh onto eleven bucks each, which activates my cheapskate gene.

    Worn OEM skid shoes
    Worn OEM skid shoes

    You can see from the markings that the slots are about twice as long as they need to be, so I figured I could replace them with some random angle iron. Might not last as long, but far less expensive.

    Bedframe skid shoe
    Bedframe skid shoe

    Having a nearly infinite supply of bedframe steel in the heap, I chopped off two suitable lengths, poked 3/8″ holes into the appropriate spots, then milled short slots to get some adjustability.

    Bedframe steel is about the nastiest stuff you (well, I) can still machine: high carbon, fine blue-hot chips, and hard edges. It might actually be better-suited for skid shoes than the soft steel OEM parts.

    They’re not pretty, but the driveway hasn’t complained yet.

    The only real problem is that those sharp corners snag on the edges of what we loosely term “the lawn”. I should apply the smoke wrench, miter the corners, and bend the edges upward. If I’m going to all that trouble, I should also hitch up the buzz box and wave some hardfacing ‘trodes over the bottom.

    But that’s in the nature of fine tuning and sounds a lot like work.

  • Stainless Steel Rule vs Ferric Chloride: Oops

    This is truly embarassing: I managed to leave a steel rule (not a ruler in the shop) atop a sploosh of ferric chloride for far too long. I eventually noticed the corrosion creeping around the edges.

    Top corrosion
    Top corrosion

    The bottom was hideous.

    Bottom corrosion
    Bottom corrosion

    So I sprayed it down with TopSaver, applied fine sandpaper, applied a Scotchbrite pad, and it came out surprisingly well.

    After treatment
    After treatment

    The ferric chloride, of course, came from a circuit board etching project. How you’re supposed to prevent that is to cover everything for about six feet around the spot marked X, but I don’t do that nearly as often as I should.

    Mostly I lay a sheet of packing paper atop the workbench and whisk it into the trash when I’m done, but this time I’d left it in place because my resistance soldering gizmo wound up anchoring the far end. Soooo, a drop or two soaked into the paper and of course the ruler wound up exactly atop that spot.

    The stuff is murder on stainless steel sinks, too…

  • Debugging Tube Circuitry: Open Resistor

    Open 2.2 meg resistor
    Open 2.2 meg resistor

    I dropped in to mooch some female header strips from my buddy Eks (which is not nearly as obscene as it sounds) and got the story behind this innocent-seeming 2.2 megohm carbon-composition resistor.

    It seems he was debugging a defunct tube-based audio amplifier. He’d probed everything and discovered that the grid bias on one of the tubes was totally wrong, which caused protracted headscratching over the associated circuitry.

    Now, in semiconductor work, a 2.2 meg resistor is an open circuit compared to the other circuit impedances. In fact, you can use pretty nearly any resistor with green or blue in the third band as a standoff in Manhattan-style construction in place of those small insulated pads.

    Megohm-value resistors are actually useful in tube circuitry; you’ll see plenty of green and blue bands sprinkled around those sockets. Although we didn’t get into details, I suspect this one was part of a grid-leak bias circuit that holds the grid voltage just a bit below the cathode; the bias comes from the few electrons that whack into the grid wires rather than passing through, so the total DC current is in the microamp range.

    After more headscratching, Eks yanked this resistor, measured it, and found it was a completely open circuit. A 2.2 meg resistor isn’t all that much different from an open circuit (it’s hard to tell the difference with an in-circuit measurement) when used in a transistor circuit, but the difference separates correct function from failure for a tube amp.

    Eks swapped in a new resisistor and the amp worked fine. Case closed!

    The digital multimeter in my desk drawer tops out at 2000 kΩ, which shows you just how much demand there is for high-value resistors these days…

  • Write Down What You Learn Where You’ll Need It

    A discussion there reminded me to mention a good habit taught by my buddy Eks: when you must look something up, write the information where you’ll see it the next time you need it.

    So, for example, each of the van wheels sports its own tire-rotation schedule inside the cover. When it’s time to swap tires in early spring and late autumn, I pry the cover off, read where the tire should go, and do the deed. I write ’em down four or five years at a time, so there’s not much thinking involved.

    The engine compartment has all the most-often-used wrench sizes and capacities.

    I write the oil change & inspection info in the maintenance schedule booklet that came with the van, although after a decade that’s pretty much full up.

    Sharpies FTW!

  • ICOM IC-Z1A Tone Squelch: Fixed?

    ICOM IC-Z1A HT with UT-93 Tone Board
    ICOM IC-Z1A HT with UT-93 Tone Board

    A few days ago I rode off to an eye doctor appointment and my ladies rode off later to meet me at the grocery store after they stopped in the garden to harvest root crops. This sort of thing is easy enough to synchronize with amateur radio, but this morning I didn’t hear a thing until they rolled up beside me in the store parking lot.

    It seemed they could hear each other and me, but I couldn’t hear either of them. We’re all on 144.39 MHz, the APRS data frequency, with 100 Hz tone squelch to keep the robots out of our ears. Our daughter has the GPS APRS tracker feeding data into the mic input, which is why we’re using a data channel for tactical comm.

    This has happened once or twice before, but it’s very intermittent. I now had sufficient motivation to disconnect the radio, an ancient ICOM IC-Z1A, from the bike and pith it on the Electronics Workbench for examination. The UT-93 Tone Squelch board is unplugged & flipped over, resting on the front half of the radio body at the lower-left of the photo.

    Turns out that there’s nothing visibly wrong in there. I suspect it’s a molecule or two of oxidation on the (gold-plated!) connector between the UT-93 and the main board, because the UT-93’s held firmly in position by the black foam square you can see in the lower-left of the photo. The small white plug near the top of the UT-93 mates with the equally small socket on the main board, just to the left of the lithium secondary cell in the middle.

    It’s all CMOS logic, of course, and there’s no actual load current involved. That’s the worst condition for contacts, as a dry connection simply doesn’t produce enough energy to burn through the least hint of oxidation. That’s why they use gold plating on connectors, but it’s been a long time since that board has moved at all; the foam square is deeply indented.

    So I wiggled & jiggled all the ribbon-cable connectors while I was in there, buttoned everything back up, and the tone decoding works again. I hope this will continue…

    Memo to Self: remove only the four black corner screws on the upper case, plus the two silver screws near the very bottom inside the battery compartment, and the two halves pop apart. No need to remove the mic and earphone plugs, whew!

  • Mysterious Noise in Toyota Sienna Minivan: Fixed!

    For about the last week I’ve noticed a soft clicking-buzzing sound somewhere near the dashboard / center console of our 2000 Toyota Sienna. I tried some on-the-fly isolation, but it wasn’t related to motion, engine on/off, CD or tape player, fan, or anything else. Finally Mary noticed it, too, and we spent half an hour in the garage yanking fuses and wiggling things until we tracked it down to below the passenger seat.

    Now, in the good old days, that was empty space, but in the Sienna it’s where the rear-area heater lives. Shoving the seat forward to the stop exposed the heater and, sure enough, it’s buzzing and clicking. Intermittently, somewhat randomly, but very steadily.

    Rear Temperature Control
    Rear Temperature Control

    With that as a hint, I twisted the rear-area temperature control (on the headliner behind the driver seat) and shazam the noise stopped. The control has detents and when moving the control to each detent the heater makes a faint buzzing. I suspect the control adjusts a valve that regulates engine coolant flow inside the heater.

    It’s not obvious whether the control is a pure-digital rotary encoder or a potentiometer, so I decided to investigate: it’s already sorta busted, what’s to lose? The bezel comes off by prying its door-side edge outward. The white plastic frame has two screws into the metal structure under the roof. The two electrical connectors are, of course, the positive-latching kind that you pull the little tab until you break your fingernail and then realize that you should push it instead.

    Temperature Control - Interior View
    Temperature Control – Interior View

    Taking the control apart reveals that it’s a potentiometer with some switching contacts. The two bifurcated spring-finger contacts on the black plastic disk short the resistive element to the inner metallic track.

    Resistive Element
    Resistive Element

    The metal contacts appeared slightly grody, but with no major corrosion. The resistive track looked just fine.

    The offending control position would be to the left side of the element as shown in the pictures here: there’s nothing obviously wrong at that spot. I think the maximum-heat position is off the resistive element entirely, resting on the far left end of the metal traces, but the control wasn’t quite set to that spot. Perhaps the problem was that the contacts became intermittent at the exact edge of the element.

    I smoothed the collection of anti-oxidation grease over the tracks, covered the contacts with their own blobs, put everything back together, and it works fine.

    We tend to put the control at A/C during the summer and at maximum heat during the winter. I suppose the poor thing got frustrated after we moved it a month or so ago…

    The money saved with this repair might just pay to have the Toyota dealer replace the spark plugs. The shop manual says that task starts by removing the windshield bezel and all the stuff above the engine intake manifold; the job costs upwards of 300 bucks. I can barely see the rear plugs with a looong inspection mirror angled just so while lying on the floor under the van, so it’s truly a nontrivial operation.

    I [delete] all over their [censored]…