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

Sears Kenmore HE3 Washer: Tub Teardown 1

The discussion following that post prompted me to take a closer look at the corroded spider. I planned to pull the spider off the back of the drum and examine the pieces, but a week of dribbling thread lube around the bolts left two of them firmly affixed.

While I don’t have it completely apart yet, some observations are in order…

Spider mounting bolts through drum

The bolts are stainless steel and utterly immovable with the usual screwdriver-handle-mounted Torx bit. I got the first two bolts out by putting a T30 bit in a 1/4-inch socket in a ratchet wrench and applying brute force.

A few days of thread lube (the incomparable PB B’Laster) persuaded two more out of their lairs. The remaining bolts may require even more brute force, but I’ll give the lube a few more days to work its magic.

Despite that, the bolts and holes are not corroded. They may have some thread locker down in there, but I see little evidence of that. I think it’s just a case of being torqued down hard, then set adrift in ionic water for half a decade.

The outer third of each arm has a covering of corrosion products, but the metal below that (now dried and flaking) gunk seems undamaged. The arms have severe corrosion and cracking throughout the inner two-thirds of their length.

Spider corrosion

If this were chemical corrosion, I’d expect it to apply evenly throughout the length of the arm, because the presence of corrosion products over the entire arm indicates pretty good distribution.

However, galvanic corrosion should follow the same pattern, so I’m not sure what to make of this.

The fact that an oxidation layer on the stainless steel tends to passivate it may not really matter. Compare the surface areas of the drum and the spider: there’s a whole lot more drum than spider, so even a passivated drum could provide enough current to rot the spider.

The ends of the spider spend their lives whipping through the water inside the tub at a pretty good clip. That could dislodge most of the crud and leave them reasonably clean, at least compared to the hub that moves more slowly (same rotational speed, smaller radius). It’s also true that the water level never reaches the hub, remaining below the level of the door seal.

Thus, the hub probably gets splashed, but never immersed, and thus has no way to remove any contaminants. The corrosion products simply build up there, keeping it wet throughout its life.

I maintain there’s little drying going on, even with the door open, in the relatively short intervals between washings. The hub region would be least likely to dry, however, because there’s absolutely no ventilation back there.

All that notwithstanding, this corrosion should not happen.

I’d very much like to see some measurements: we’re all obviously guessing at the conditions. The plastic tub surrounding the drum has a port for the rear vent near the perimeter, so it’s possible to get a (cramped, inconvenient) look in there without tearing the washer apart.

More later, after I get the mumble thing apart…

2010-08-16
Earbud Cushion Replacement

Somehow I managed to shred the silicone cushion of the earbud on my bike radio. As nearly as I can tell, it got caught between the seat and the back; the missing part certainly isn’t inside my ear.

Anyhow, I have a bag of spare cushions from all the other earbuds, so this isn’t a showstopper.

The adhesive snot holding the earwax filter in place also failed, so I figured I should fix that while I had the hood up. The old filter was all ooky with earwax & oil & dried sweat, which meant that any new adhesive wouldn’t stick. I chopped a disk from a random foam earbud cover with a 7/32-inch hollow punch and glued it in place with some acrylic sealant.

Earbud cushion and wax filter replacement

While I had the sealant out, I replaced the tape sealing the vent hole (on the other end of the earbud) with a dot of glop, much as I should have done originally.

2010-08-11
Bicycle Tire Liners FTW!

Gashed tread

We’re getting set up for a bicycle vacation and I did a quick tire inspection… good thing, too, considering the gashes I found in the rear tire on Mary’s Tour Easy.

I put Schwalbe Marathon 700x35C tires on the back of our ‘bents, for well and good reason: Marathons have plenty of rubber and include a Kevlar puncture-resistant layer. In this case, that was just barely enough!

Here’s a cross-section through the tire; the Kevlar layer is yellow, with the tire carcass fibers inward of that.

Schwalbe Marathon tire cross-section

The greenish-yellow tint in the left-hand gash (in the top picture) is the Slime tire liner (they prefer “tube protector”) showing through. Here’s what the liner looked like after we pulled the tire off; the liner shows some damage, but it’s just surface scuffing.

Scuffs on tire liner

Quite by coincidence, the gashes straddled the overlapped end of the liner. The end of the liner is on the tube side; I haven’t trimmed or tapered the end of this one.

Here’s what the inside of the tire looked like; the Kevlar fought the gashes to a standstill and left the carcass mostly intact. The painted and illustrated fingernails belong to my shop assistant.

Scuffs inside tire carcass

Here’s a cross-section through the Kevlar layer. I don’t know what Mary ran over, but it was most likely a sizable chunk of the broken glass that litters the roads around here. I doubt anybody gets prosecuted for littering, but as far as I’m concerned, a fitting punishment would be collecting the glass from a few miles of roadway: crawling on hands and knees, picking up fragments with their lips.

Cuts through tire anti-puncture layer

I put a new tube in a new Marathon (for obvious reasons, I have a supply of both on the shelf at all times), we positioned the liner, pumped it up, and it’s all good.

2010-08-08
External Li-Ion Pack Intermittent Connection: Solved!

After all the hassle of dismantling the battery pack, removing the jack from the board required nothing more complex than a solder sucker.

Coaxial power jack – solder side

With the jack in hand, I idly poked a coaxial plug into it and realized that the amount the plug stuck out was just about exactly equal to the thickness of the black plastic cap on its tip. Some rummaging turned up one of the six plugs with a missing tip, at which point both the problem and its solution were obvious.

Broken vs original coaxial power tips

A bit of tedious work with a tiny screwdriver and a needle convinced the socket to disgorge the plastic ring from its bowels …

Broken tip extracted from jack

Now, I suppose I could have figured this out without taking the case apart, but actually fixing the problem would still require surgery, soooo there’s no wasted effort. That’s my story and I’m sticking with it.

If you think you could extract that ring from the outside, there’s a joke about that.

I put the case back together with a few dabs of silicone snot adhesive (despite what I know about letting acetic acid loose near electronics) to anchor the circuit board, applied a belly band of tastefully color-coordinated (i.e. silver) duct tape, and it’s all good.

Actually, the pack was stone cold dead until I plugged it into the charger to reset its battery protection circuitry. Evidently, disconnecting and reconnecting the battery tripped the protection logic. I’ve seen that in other Li-Ion packs, so it wasn’t quite so scary as it was the first time around.

As for the coaxial power tip: a dab of solvent glue, an overnight clamping session, and I think it’ll work fine forever more.

I should machine up some stabilizing collars around the sockets to match that obvious shoulder on the plug, shouldn’t I?

2010-08-07
External Li-Ion Pack Intermittent Connection: Dismantling the Pack
The power lead into the Li-Ion pack I’m using for the bike radio became badly intermittent on a recent ride. When I got back I swapped in a different pack and the problem Went Away, but I noticed that the coaxial power plug didn’t seem to seat all the way into the jack on the failed pack. I’d noticed that before, although I attributed it to getting two different sets of the packs; it didn’t seem to make any difference.

Given that I was going to have to either repair or replace the jack, dismantling the offending pack was next on the list. Some preliminary poking showed that there were no screws concealed under the label, so the two halves of the pack were either snapped or bonded together.

The case didn’t respond to the usual wedging and prying by revealing an opening, which suggested that it was bonded. That meant I must saw the thing apart.

I set up a 31-mil slitting saw on the Sherline and clamped the pack atop a random plastic slab atop the tooling plate. The Sherline’s limited throat depth meant I had to cut the far side of the pack. I aligned the saw to the Z-axis level of the joint along the middle of the pack by eyeballometric guesstimation.

Slitting saw setup

Key point:
- You absolutely do not want to saw into a lithium-ion cell, not even a little bit.
Therefore:
- The pack must be aligned parallel to the cutter’s travel
- The cuts must proceed in tiny increments, and
- You must verify that each cut doesn’t reveal any surprises.
In this setup, the pack aligns against a clamp on the left side and to a parallel block (removed while cutting) along the rear edge of the tooling plate. I could then unclamp the pack, rotate it to put the next edge in place, and use the same XYZ origin with the edge parallel to X.

Here’s the view from the back of the table.

Sawing the case

I ran the spindle at 5 k RPM and cut about 15 inch/secminute. I’m sure the pros do it faster, but that was enough to warm up the blade and that’s fast enough for me. [Update: typo on the units. Thanks!]

Cuts were 0.020 inch per pass, which is about 0.5 mm. I expected the case to be some hard-metric dimension and wasn’t disappointed.

After the cuts reached 0.060 inch, I manage to pry the remaining plastic in the joint apart and split the halves apart along the connectors and LEDs at the front where I couldn’t do any sawing.

Here’s a close look at the cut, just above the battery terminals. The case turned out to be 2 mm thick, about 0.080 inch, so I was just about all the way through. The cut was perfectly aligned with the case and cracked open neatly along the entire length.

Tight tolerance on the cut depth

An interior view, showing that the cells adhered to the left half of the case and the electronics to the right: of course. I pried the cells loose from the left side, which provided enough access to unsolder the things, as the terminals were against the case. Notice that there’s absolutely nothing between the inside of the case and the outside of the cell, so cutting just slightly too deep would be a Bad Thing™.

First look inside the case

After a bit of work, here’s the entire layout…

Battery pack internal layout

Much to my surprise, the battery consists of two series-connected sets of three cells: 2 x 3.7 V = 7.4 V. I expected three series sets for about 3 x 3.7 = 11.1 V, with a linear regulator down to the 9.0 V output.

As it turns out, they used two switching regulators: the one between the two triplets controls the charging voltage and the one to the lower-left boosts the battery to the pack’s 9.0 V output. I had hoped for a resistor divider that I could tweak to get 9.6 V out, but it certainly wasn’t obvious.

I unsoldered the cells, dismounted the circuit board, and puzzled over it for a bit, after which the problem was obvious.

The story continues tomorrow, with a dramatic denouement…
2010-08-06
Replacement Skinny Pin Punch Pin

I have a quartet of nice pin punches with hardened pins in various diameters. I managed to drop the smallest punch, didn’t get my foot under it in time, it struck sparks from the concrete floor when it hit, and the pin snapped.

Not being able to replicate the pin’s neat mushroom head, I contented myself by chopping off a length of music wire and grinding the ends flat. Annealed one end over the kitchen stove, whacked it with another punch to get a flat, and it’s all good.

Replacement pin for punch

The music wire isn’t quite perfectly straight, but you don’t beat on things with a 40-mil punch, anyway.

2010-08-05
CPU Heatsink Fuzz

My PC makes a seasonal migration: to the basement during the summer, to the living room in the winter. Those moves provide an opportunity to vacuum the fuzz out of the fan grilles and heatsinks.

You’d think that, given the trouble caused by blocked air inlets, manufacturers would make it easy to get access to the grilles and trivially easy to remove the fuzz. Not so, alas.

This time, I decided to see what the intake side of the main heatsink looked like. Two screws secure the shell to the circuit board and provide clamping pressure on the CPU heat spreader. The heatsink is a massive affair with liquid-filled heat pipes; I’ve never taken it out before because removing the screws exposes the CPU heat spreader, where you do not want to get fuzz.

Heatsink fuzz

Oops!

A bit of work with the vacuum and a brush greatly improved the situation. I think I kept the fuzz out of the heatsink-to-CPU joint, but there’s really no way to know because, as nearly as I can tell, Dell didn’t include any of the CPU temperature readouts on this system board.

Memo to Self: Gotta do that more often …

2010-08-02