Posts Tagged Repairs

Hotrod M2 Platform Support Stud Repair

The hotrod build platform I’m using with the Makergear M2 consists of a PCB heater bonded to a glass plate, supported by three socket head cap screws soldered into the PCB. The print quality recently took a nosedive that seemed related to the first layer height, with which I fiddled more than usual, and finally the front of the platform became obviously, visibly, no-way-around-it far too high. Peering under the platform showed that the front support stud had pulled out of the solder fillet securing it to the PCB:

M2 Hotrod Platform - support stud pullout

M2 Hotrod Platform – support stud pullout

Those PCB patterns conduct the heater current around the mounting holes: the hotrod platform has better heat distribution than the OEM M2 platform.

The offending screw didn’t go anywhere:

M2 Hotrod Platform - support stud in spring

M2 Hotrod Platform – support stud in spring

The wavy spring and silicone plug press on the PCB, so the solder fillet had to support all the stress. It seemed as though the solder hadn’t bonded to the stainless SHCS, but, rather than try to fix that, I decided to put a washer on the screw. That way, the spring bears on the washer and the screw head supports the strain, with the solder fillet responsible for holding the PCB and glass plate in position.

Alas, I didn’t have any washers small enough on the inside (3 mm) and big enough on the outside to support the springs, so I cut some out of a sheet steel scrap by drilling the center hole to the proper diameter, then applying a hole saw without its (far too large) pilot drill:

M2 Hotrod Platform - hole-sawing washers

M2 Hotrod Platform – hole-sawing washers

That’s a lethally bad idea, as the pilot-less saw can grab the sheet and toss it across the shop. Notice the screws holding the sheet down and absorbing the cutting torque, plus the two clamps enforcing the “stay put” edict.

The other problem with not having a pilot drill in the hole saw is that it’s not guaranteed to cut a cookie that’s concentric with the center hole. Instead of taking the time to make a pilot, I just drilled and cut a few extra washers, then picked the best three of the set for finishing:

M2 Hotrod Platform - rough-cut washers

M2 Hotrod Platform – rough-cut washers

Using a screw as a mandrel, I lathe-turned the OD of the better ones to make them nice and round:

M2 Hotrod Platform - washer on mandrel

M2 Hotrod Platform – washer on mandrel

Two of the three PCB support screws were in the right place (they hadn’t come loose), so I used the M2 as an alignment fixture for the third:

M2 Hotrod Platform - aligning washers

M2 Hotrod Platform – aligning washers

That’s a layer of  good old JB Industro Weld epoxy, rated for much higher temperatures than the platform will ever see, between the big washers and the PCB. I buttered up the head of the errant screw and the inside of the solder fillet, shoved it in, and then stacked everything together. The small washers held the big washers perpendicular to the screws while the epoxy cured.

After that, I removed the small washers, reinstalled springs + silicone plugs, tightened the nyloc nuts, aligned the platform, ran off a few thinwall hollow boxes, tweaked the alignment, and it was all good:

M2 Hotrod Platform - thinwall box alignment

M2 Hotrod Platform – thinwall box alignment

The rest of the story: that mumble screw pulled loose on the Friday evening before the Mini Maker Faire on Saturday morning. I did all the shop work after supper, then let the epoxy cure overnight with the platform set to 95 °F while I got a good night’s sleep. Reinstalling and realigning the platform took the better part of half an hour around breakfast, after which I tore it all down, packed it all up, and headed off to the Mini Maker Faire.

In truth, that’s the most trouble I’ve had with the M2 and it’s not Makergear’s fault: it’s not their platform. After reinstalling the platform, the alignment was no big deal and it’s been stable ever since.

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Trust Multimedia Mouse: Gummy Rubber

While looking for something else, I found the old Trust Multimedia Mouse and discovered its nice grippy rubber surfaces had become adhesive slime. Graduated efforts with water, rubbing alcohol, and denatured alcohol being unavailing, I finally hit it with xylene and that did the trick:

Degummed Trust Mouse

Degummed Trust Mouse

Of course, xylene also wiped away the fancy button markings and irretrievably scarred the surface, but at least I can pick the mouse up without having it stick to my hand. Not that I pick it up that often, obviously.

Several other gadgets have a similar grippy finish, so now I know what to do when it turns gummy: throw the gadgets out…

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Eyeglass Temple Spring Repair

Another of Mary’s glasses snapped at the temple joint:

Broken eyeglass temple spring

Broken eyeglass temple spring

This one has a spring inside the joint that latches the temple on either side of that square inner corner. Obviously, there’s no way to reconnect the broken stub with the spring retracted inside the brazed temple box, so:

  • File off the corner
  • Fill the socket with epoxy
  • Ease the stub in place
  • Wipe off the excess epoxy
  • Align on the workbench
  • Let it cure overnight

At least the hinge folds again, even if the spring doesn’t work:

Broken eyeglass temple spring - epoxied

Broken eyeglass temple spring – epoxied

She promises to scrap out her oldest glasses after the next eye exam…

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Heating Blanket Controller: Soldering QC

A friend reported that three of the four heating blankets he’s bought over the last several years have failed, so he sent the lot to me for teardown and maybe repair.

Looking inside one controller showed some obviously bad solder joints:

Blanket controller - bad joints

Blanket controller – bad joints

Hitting the joints with the soldering iron improved their outlook on life, but the controller remained dead; they weren’t really bad joints, they just looked that way.

If the “lot number” labels on the controllers mean anything, they’ve tried three different triac mounts over the years:

  • A through-hole triac screwed to the board with no heatsink
  • An SMD triac using the PCB copper as a heatsink
  • A through-hole triac with a big aluminum heatsink

That’s in order of ascending lot number, suggesting the triac caused some reliability problems.

I’m still trying to figure out how to probe the circuitry without killing myself. An isolation transformer comes to mind, because the blanket dissipates only 85 W.

Surely the triacs have snubbers…

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Shaft Position Sensor: Trimpot Wrench

With the shaft position sensor mounted in this position:

Kenmore 158 Shaft position sensor - overview

Kenmore 158 Shaft position sensor – overview

There’s no way to get a screwdriver into the trimpot that adjusts the sensor’s trip point.

A few minutes with tin snips, nibbling tool, and square file produced a small wrench:

Trimpot Wrench

Trimpot Wrench

One side of the wrench has a 45° bend that made tweaking the pot just slightly easier.

The proper trip point turned out to be about 90° away from where the trimpot started, with the level midway between the detection points for shiny metal tape and the cutout side of the counterweight.

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Doorbell Switch Corrosion

A friend, anticipating a stream of visitors for their freshly hatched baby, asked for help with a defunct remote doorbell. A bit of probing showed that shorting across the pushbutton switch contacts reliably triggered the bell, so I unsoldered it:

Doorbell switch - intact

Doorbell switch – intact

A similar switch from the heap had a longer stem that was easy enough to shorten, so the repair didn’t take very long at all: ya gotta have stuff!

An autopsy reveals the expected contact corrosion:

Doorbell switch - parts

Doorbell switch – parts

Underexposing the image by about two stops retained some texture on the contact dome.

The IC date codes suggest the box is over a decade old, which is as much life as one can expect from cheap consumer electronics, particularly with an unsealed switch placed outdoors.

It’s probably good for another decade…

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NYS DOT Patch Quality

After years of neglect, an NYS DOT crew started a really nice repair job on the inside edge of the curve just north of our house. They milled out the deteriorated road surface, cleaned out the debris, and laid in a patch flush with the road surface. That’s quite unlike their usual shovel-some-cold-patch / hand-tamp / drive-over-it process, made familiar everywhere else around here.

Unfortunately, for unknown reasons, they didn’t fill in the last two feet of the milled-out trench, leaving a tooth-shattering pair of perpendicular edges exactly where you’d least expect them:

Rt 376 north of Heathbrook - unfinished patch

Rt 376 north of Heathbrook – unfinished patch

Ran out of asphalt? Lunch break? Called off to another emergency? We’ll never know.

I sent a note, with that picture, to the NYS DOT Bicycle & Pedestrian Coordinator, asking what happened; perhaps they planned another layer atop the whole curve to seal the rest of the cracked pavement?

The next day a crew filled in the hole, which I find far more than coincidental.

Although it’s better than it was, there’s now a joint that will deteriorate more rapidly than the uniform asphalt layer they should have created.

We’ll take what we get…

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