Posts Tagged Repairs

Mis-Punched Scope Probe Hook

Back in the day, HP scope probes had a rugged music-wire hook on the tip:

HP scope probe tip

HP scope probe tip

These days, scope probe tips use ordinary sheet steel punched into a hook shape:

Siglent scope probe - good tip

Siglent scope probe – good tip

By sheer bad luck, the first probe out of the bag had a mis-punched end with no griptivity:

Siglent scope probe - mis-cut tip

Siglent scope probe – mis-cut tip

Dunno what happened, but it was definitely sheared off in the factory.

After I finally recognized the problem, I shaped a crude hook with a safe-edge needle file and continued the mission:

Siglent scope probe - filed tip

Siglent scope probe – filed tip

A quick note to Siglent put a replacement probe tip in the mail, so it’s all good.



Fluorescent Shop Light Ballasts, Redux

As usual, several shoplights didn’t survive the winter, so I gutted and rebuilt them with LED tubes. Even the fancy shoplights with genuine electronic ballasts survive less than nine years, as two of those eight “new” lamps have failed so far.

The dead ballast looks the same as it did before:

Electronic ballast - label

Electronic ballast – label

Some deft work with a cold chisel and my Designated Prydriver popped the top to reveal a plastic-wrapped circuit board:

Electronic ballast - interior wrapped

Electronic ballast – interior wrapped

Perhaps the flexy gunk reduces the sound level:

Electronic ballast - interior A

Electronic ballast – interior A

While also preventing casual failure analysis and organ harvesting:

Electronic ballast - interior B

Electronic ballast – interior B

The black gunk smells more like plastic and less like old-school tar. It’s definitely not a peel-able conformal coating.

One the other paw, the two magnetic ballasts in another lamp sported actual metal-film capacitors, which I harvested and tossed into the Big Box o’ Film Caps:

Shoplight choke ballast - film cap

Shoplight choke ballast – film cap

If a dying ballast didn’t also kill its fluorescent tube(s), I’d be less annoyed. I’m running the remaining tubes through the surviving fixtures, but the end is nigh for both.

The new LED tubes produce more light than the old fluorescents, although I still don’t like their 6500 K “daylight glow” color.



Snowblower Muffler Bracket

After three years, the bracket locking the snowblower’s muffler bolts broke, but this time I saw the bolt pop out of the muffler, fall to the driveway, and lie there sizzling in the slush. I tightened the remaining bolt and completed the mission.

The OEM bracket was thin sheet metal and broke across one bolt hole under the head. I sawed a rectangle out of a defunct PC case, then drilled clearance holes:

Snowblower muffler - drilling bracket

Snowblower muffler – drilling bracket

Bending two corners upward locks the bolt heads in position. I started the bends by clamping the bracket in the bench vise and whacking the corners, then finishing the job with a drift punch after installing it:

Snowblower muffler installed

Snowblower muffler installed

Of course, I renewed the Never-Seez on the bolt threads; they obviously weren’t corroded in place!

For whatever it’s worth, the many spot welds joining the top bracket to the muffler are doing just fine.


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Baofeng BL-5 Pack Rebuild

The 18650 cell protection PCBs with 8205 ICs arrived and seemed small enough to simply tuck into the gap between the rounded cells in the second Baofeng BL-5 pack:

Baofeng BL-5 - new protection PCB - wiring 1

Baofeng BL-5 – new protection PCB – wiring 1

For whatever it might be worth, you’re looking at the only Baofeng battery pack containing an actual 10 kΩ thermistor, harvested from the benchtop Tray of Doom:

Baofeng BL-5 pack - thermistor

Baofeng BL-5 pack – thermistor

Unfortunately, the components on the PCB stuck up a bit too far from the cell surface and held the lid just slightly proud of the case. Applying pressure to lithium cells being a Bad Idea, I rearranged the layout by flipping the cells over, tucking the PCB components between the cells, and connecting everything with nickel tape instead of insulated wires:

Baofeng BL-5 - new protection PCB - wiring 2

Baofeng BL-5 – new protection PCB – wiring 2

The snippets of manila paper and Kapton tape hold things apart and together, as needed. Looks ugly, fits better.

Pop it in the charger to reset the protection PCB lockout and it’s all good again.

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Bench Leg Repair

A long long time ago, I conjured a short bench for our Larval Engineer from a pair of junked folding-table legs and a truly hideous mid-50s Genuine Formica countertop salvaged from the kitchen refurbishment:

Bench Leg - overview

Bench Leg – overview

Most recently, it held a pile of test equipment and random stuff next to the MPCNC, whereupon the welds holding the tube with the feet to one of the vertical tubes on the far end failed. It wasn’t in the critical path, so I broke the welds on the other tube, propped the vertical tubes on wood blocks, and continued the mission. Having finally finished those measurements, I could clear off the bench and repair the legs.

I no longer have my welding gear and, in any event, it’s still winter outside, so a low-excitement repair seemed in order: drill suitable holes into the leg crosspiece, make threaded inserts for the tubes, and join them with 3/8-16 bolts.

So, we begin.

File the broken welds off the foot tube, align it in the drill press vice (where it barely fits!), center drill to make a pilot hole, then poke a 3/8 inch drill completely through to line up both holes:

Bench Leg - through drilling

Bench Leg – through drilling

By the Universal Law of the Conservation of Perversity, a 3/8 inch bolt didn’t quite fit the 3/8 inch hole, so I embiggened the holes with a step drill:

Bench Leg - step-drilling to size

Bench Leg – step-drilling to size

The step drill obviously has hard metric diameters labeled as weird inch sizes:

Quasi-inch step drill

Quasi-inch step drill

I can’t read the second step, either, but it’s apparently 25/64 inch = 9.8 mm, which is just enough over 3/8 inch = 9.5 mm to be useful. The next step is 14 mm = 35/64 inch, so the drill is a bit of a lump.

The leg tubes were a hair over 0.9 inch ID and not particularly round. Tolerances being slack, slice a bit more than two inches off a 1 inch OD aluminum rod:

Bench Leg - sawing rod stock

Bench Leg – sawing rod stock

I wanted more than one diameter in the tubes, but the bolts in my stash topped out at 2 inches and, really, an inch of aluminum won’t go anywhere.

Clean up one end of the rod to 0.9 inch OD, flip, and center drill:

Bench Leg - center drilling insert

Bench Leg – center drilling insert

Obviously, surface finish and concentricity aren’t critical, but the cleaned-up OD of the left end lined up at  barely perceptible mismatch with the (yet to be done) right end.

Sunder in twain:

Bench Leg - sawing leg inserts

Bench Leg – sawing leg inserts

Betcha you can’t spot the junction between the two ODs, either.

Drill 3/8 inch through, then discover you (well, I) have neither a drill big enough nor a boring bar small enough to embiggen one end of the hole for a nasty interference fit against the tips of a 3/8 inch hex nut.

Once again, a step drill to the rescue:

Bench Leg - step-drilling insert

Bench Leg – step-drilling insert

Because it’s a step drill, the counterbore isn’t quite deep enough for the whole nut, so turn the nut to fit the recess left by the drill:

Bench Leg - nut shaping

Bench Leg – nut shaping

Put a bolt through the insert as a guide, spin the nut on, backstop the insert with a machinist’s parallel jaw clamp (loose, just to give the head somewhere to go), line ’em up, and mash the nut into place with the bench vise:

Bench Leg - nut pressed in place

Bench Leg – nut pressed in place

Clean up the broken welds with a rat tail file, hammer the inserts into the tubes:

Bench Leg - insert installed

Bench Leg – insert installed

Which, as I expected, rounded them nicely while producing an absolutely solid, ain’t gonna work loose, dry joint.

Add threadlocker to the bolts and it’s all good:

Bench Leg - repaired

Bench Leg – repaired

Stipulated: butt-ugly.

Tell me you’d have fish-mouthed those inserts just for pretty, after noting the factory didn’t bother fishmouthing the vertical tubes before welding them in place.

But it was good for generous dose of Quality Shop Time!


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Streaming Radio Player: Timing Tweaks

Slowing the SPI clock and updating the drivers having had no noticeable effect on the OLED display corruption, I once again pondered the SH1106 controller timing specs.

The chip reset seems remarkably slow, even at maximum VCC:

SH1106 - Reset Timing Specs

SH1106 – Reset Timing Specs

I think the relevant code is in the luma.core driver’s file. On the RPi, it resides in /usr/local/lib/python2.7/dist-packages/luma/core/interface/.

As far as I can tell, the bitbang class handles all the setup and teardown around the actual data transfers, but it’s not clear (to me, anyway) how it interacts with the underlying hardware SPI machinery.

So, let’s add some sleepiness to the Reset code:

        if self._RST is not None:
            self._gpio.output(self._RST, self._gpio.LOW)  # Reset device
            self._gpio.output(self._RST, self._gpio.HIGH)  # Keep RESET pulled high

A few milliseconds, rather than a few (hundred) microseconds, won’t make any perceptible difference.

Similarly, the Chip Select and Address (Command/Data) signals require more delay than might occur between successive Python statements:

SH1106 - SPI Address and Select Timing Specs

SH1106 – SPI Address and Select Timing Specs

This should do the trick, again with excessive delay:

        if self._DC:
            self._gpio.output(self._DC, self._cmd_mode)

... snippage ...

        if self._DC:
            self._gpio.output(self._DC, self._data_mode)

... snippage ...

        if self._CE:
            gpio.output(self._CE, gpio.LOW)  # Active low

... snippage ...

        if self._CE:
            gpio.output(self._CE, gpio.HIGH)

Although it shouldn’t be necessary, I blew away the pyc files to prevent future confusion over who’s doing what with which.

Once again, this will require several weeks to see whether the situation changes for the better.



Sena PS410 Serial Server: Burnin’ In

The USB serial adapters I use to capture HP54602 scope and HP8591 spectrum analyzer screenshots, as well as monitor the HP Z8501 GPS time standard, lack unique identifiers and appear as unpredictable device nodes.

After putting up with this for far too long, I dropped $15 on a Sena Technologies PS410 serial server:

Sena PS410 Serial Server - interior

Sena PS410 Serial Server – interior

It needed a new lithium coin cell, of course:

Sena PS410 Serial Server - as-received CR2032

Sena PS410 Serial Server – as-received CR2032

The PCB and chip date codes suggest a 2009 build, so “98” might mean August 2009. Whether that’s the manufacturing date or the best used by date, ya never know.

The eBay deal didn’t include the power supply, so I hacked a coaxial jack on the back:

Sena PS410 Serial Server - hacked power jack

Sena PS410 Serial Server – hacked power jack

A 14 VDC IBM laptop brick from the pile suits the “9 to 36 V” range printed on the case.

Poking the “factory reset” switch did what you’d expect and the “console” serial port on the front worked fine. I plugged in the scope, the spectrum analyzer, and the GPS receiver, whereupon the bench took on the unmistakable aroma of electronic death:

Sena PS410 Serial Server - charred ferrite chip

Sena PS410 Serial Server – charred ferrite chip

Some probing suggests FB9 used to be a ferrite bead between serial port 2’s ground pin and the frame ground.

To compress an afternoon of tinkering into one sentence, there seems to be an occasional 35 VAC difference between the spectrum analyzer and the scope, but only when one or the other is plugged into the PS410. Everything is (now!) plugged into the same branch circuit and, in fact, the same outlet via many power strips, but the difference remains. A different power supply makes no difference, either.

I managed to burn out the ferrite bead on Port 1 with only the scope and the power supply plugged in, by connecting the scope’s ground lead to the shell of Port 2. That makes no sense: there is no voltage difference between the scope’s serial ground and its probe ground.

Something Is Not Right, but I’m baffled.

I have established that the server works fine, even with the charred beads, which is a Good Thing.