Repair: Mezzo ESM-008 Sewing Machine Power Jack Assembly

Sometimes, the best thing in life is not knowing what might happen next. After I repaired a washing machine using some rather funny trickery, this week, it was the sewing machine that needed attention. The particular sewing machine was a Mezzo branded ESM-008, an Aldi special.

Judging from the label, it would have been on sale in May 2006, making it almost 12 years old. But what is the failure?

Diagnosis

The patient looked okay from the front at first glance, but the problem very quickly revealed itself. Like a patient with a dislocated arm …

… this one had a dislocated socket. Namely, the panel which is involved in the power/pedal input and power switch had somehow popped out of the case entirely. A fracture in the plastic can be seen, which isn’t a great sign.

But it gets worse. With this failure, the rear portion containing exposed live contacts can be touched. I’m sure that this machine might have continued to be used if it were not for the fact that the live wire for either the motor or something else had broken out from a terminal, leaving the ring lug behind.

Repair

I suppose the good news is that the rest of the machine was mechanically sound, so there was no need for me to be concerned. First step is to get into it and get a closer look at how the assembly was supposed to be put together.

To do that, one screw can be undone from the underside to release the side panel entirely.

Inside, we see that the arrangement is like a junction box or even a hobby case. There would have been two screws securing the front portion to the rear plate, and the other two screws (visible) to secure the rear plate to the frame of the unit. It seems that the plastic they used might have been too brittle, the screws may have been overtightened causing plastic cracking or the plug may have been too forcefully pulled/pushed to cause this type of failure.

However, this does mean that there are probably loose plastic parts and screws inside the machine, so I decided to first dismount the plastic plate and the screws and then give the machine a good shakedown. While some loose plastic was dislodged, the screws I expected to find were nowhere in sight. Maybe they got lodged somewhere inside or have been long lost.

Putting the two halves together, we can see that the original eyelet for a screw/bolt has snapped, thus a different solution is required. I decided to use superglue (cyanoacrylate) as it was to hand and fairly strong, but I decided that this shouldn’t just be the only method of securing the front half.

To attend to the wire, I grabbed a section of heatshrink and used a pair of needle-nosed pliers to undo the brass nut and separate the remaining lug. I cleared off the old heatshrink off the lug and cut the new piece to “just” fit while not obstructing the joint.

As the lug was once crimped, and I have no faith in a “loose” brass crimp onto copper, I decided to solder the joint for both mechanical and electrical reasons. The heatshrink was a little short so that I could solder the lug, but in doing so, it had already shrunk over the wire due to conducted heat.

I decided to add a second layer of larger heatshrink that could go over the lug just to be safe. However, I should have probably reduced the overhang slightly to ensure even pressure all-around the brass lug. I don’t think it’s critical due to the magnitude of the current involved and the tension on the nut.

There it is, reassembled into the terminal block.

After running a bead of superglue all around the flat surfaces and pushing together for a good hold, I decided to wrap electrical tape around the two halves in the area that would not interfere with its function. By doing this, if the case halves did come apart, the tension in the tape should stop the whole thing “flopping” out immediately, giving some time for a proper reaction. The tape was a little wide, so I had to use a knife to clear out the lower power plug port.

Once reinstalled into the machine, it fits just fine with the cables tucked neatly underneath.

The final step was to reinstall the side panel and test. The machine worked just fine, as I sewed a piece of paper together, so I would call it a success.

Conclusion

This wasn’t a very complicated repair, but it is a little shocking as to how the design could easily result in live parts become exposed (e.g. tripping on the power input lead a few times might do it). Once damaged, the plastic ears on the jack panel fractured, making a perfect repair impossible. Glue will probably suffice to give the machine a little more life, but whether it is sufficient in the long run given the stresses is something that I’m not certain of. In some sense, this issue might have been reduced if the side panel cut out was smaller than the jack panel or the jacks integrated into the side panel, thus providing some more substantial mechanical support.

But anything saved from the landfill and any purchase deferred is a win in my books.

Posted in DIY, Electronics | Tagged , , | 5 Comments

Salvaged: eX-power 75Wh Laptop/USB Power Bank

Sometimes it pays to hang around various tertiary institutions. Case in point, when earlier this week, a group was moving out of their old lab into a new one. Events like these are often the impetus for a proper clean-up to be done and with every clean-up comes rubbish just ripe for the salvage. Like a vulture spotting some carrion, I was swooping down on the boxes of unwanted items and picking it apart for the gold inside.

I found two eX-power branded laptop power banks. While the brand is questionable and this style of power bank is rare to see nowadays, in the old days, if you had a laptop without a replaceable battery or the replacements were too expensive, you would use this instead as it was a portable battery that would “act” like the supplied power adapter.

I never owned such a contraption so I thought it would be nice to give them a try. I wonder if they still worked properly after all these years, as they were completely discharged when I got my hands on them. I also found two laptop-style chargers suitable for the units, but not the particular output cables. Oh well, you can’t always win.

The Units

The unit is black, glossy and plastic, and about the size of a 3.5″ hard drive. The top side has a push-button LED bar-graph charge indicator, as some older laptop batteries have.

The unit has an easily recognized 5V USB output, with a claimed current rating of 1A. This was the most easiest to test, so we’ll see about this.

The unit does have a claimed 10.8V/3A output which is marked as 9V-12V. I suspect this indicates it’s a switched/fused output from the lithium ion pack directly. As a 3S2P setup, its nominal voltage is 11.1V, but can range from a high of 12.6V down to about 8.4V.

The other output intended for a laptop is claimed to be 19V/3.5A. This suggests the most “beefy” converter inside is providing a regulated output, yet the jack itself is labelled 16-19V. I suspect this means the converter inside may not be quite sufficient to push the full voltage as the pack runs down – it is about 2:1 output voltage vs pack voltage, and thus the current load on the cells can be quite high at full output.

The total capacity is claimed to be 75Wh maximum.

The unit has ribs on the side but is not vented. It gets quite hot while charging, with the lowest unit on the bar-graph lighting red while charging and green when charged. The unit weighs 620g.

Teardown

The unit isn’t so obvious in how it can be opened. I managed to guess at where the corner screws were …

… but it still would not budge. As it turns out, there are two hidden screws along the edges.

Removing those screws, the unit was still rather uncooperative, requiring some significant force to pry apart. It is clipped together and double-sided tape on the battery also acts to hold the plastic shell together.

We can see that there is a set of nine 18650 cells, arranged as a 3S2P pack. The pack has proper balancing connections (thankfully), protecting it against cell imbalance and making the complexity of the pack comparable to replacement laptop batteries. The cells are YLE ICR18650A220, from YikLik rated at 2200mAh. In light of this, the total pack capacity is only 73.26Wh – close enough I suppose.

I wanted to know more about the switching converter PCB. It’s quite beefy and the aluminium plate serves as a heatsink. However, it wouldn’t budge, and this was down to two screws that can be accessed through holes in the heatsink. But if you’re going to undo them, you’re going to be releasing metal shrapnel into a circuit with a live beefy Li-Ion power supply connected. I don’t have the guts to do that … one short could well be catastrophic. As a result, that mystery will remain unsolved.

Testing the USB Output

As I didn’t have the appropriate connections to load-test the other outputs, I only tested the USB ports. The trusty B&K Precision Model 8600 was entrusted to perform the test. Despite the claimed 1A output, the unit always shut down immediately on 1A load, with an awful squealing noise suggesting it was critically overloaded. As a result, I had to test at 500mA which was a more sensible value.

The first day testing the first unit was quite an event as a heatwave passed through and the increased ambient seemed to cause the power bank output to drop slightly. Once night had fallen, the voltage recovered. Both units I salvaged performed almost identically, with just over 60Wh delivered at 500mA. This was more than I expected, as this is just over 80% of the label claimed value, or 82% of the actual battery capacity. When accounting for converter efficiency and battery ageing over at least five years, it’s a good result.

Being a little more daring, I pushed the current up to 800mA for a test. Unfortunately, the unit couldn’t sustain even 850mA, but the unhappy state of the converter is clear from the relatively low output voltage. No damage was caused, and the delivered charge was a little higher than the 500mA case, which was surprising.

In light of this, the USB output is actually quite limited in its usefulness. As a result, I didn’t bother assessing the ripple performance. Instead, I think I might use the other outputs with an outboard converter if I’m actually intent on using the unit.

Conclusion

I’m not too surprised that the unit didn’t seem to meet its claimed current output on USB. It’s endemic of a bigger issue – namely that of Chinese electronics which overstate their capabilities to try and appear better than the competition. Given the age and lack of reputation brand-wise, it’s not unexpected. I didn’t bother to test the ripple because it’s so painfully low that it’s not good for that much nowadays. However, when it came to output capacity, it’s nice to see that it could still manage a bit more than 80% of the rating even after half a decade or more.

Instead, it might be better just to use the laptop output or “quasi” 12v output (which might not be converted at all) into my own step-down converter to get a more beefy 5V output to charge a few devices at once.

Posted in Power Bank, Salvage | Tagged , , , , | 1 Comment

Review, Teardown: TP-Link Archer T2UHP AC600 High Power USB Adapter

I had looked at a relatively cheap dual-band 802.11ac dual-stream USB Wi-Fi adapter recently and it seemed that the pain of single-band Wi-Fi solutions may be soon coming to an end. Unfortunately, that adapter did have some design quirks and its Realtek chipset did leave something to be desired from a Linux support point of view. As a result, I decided to go looking for another adapter that had an external antenna, good range and a non-Realtek chipset. Believe me, it was not easy to find.

Behold, the TP-Link Archer T2UHP AC600 High Power Wireless USB Adapter. This unit cost a lot more at AU$52, but is based on a Mediatek MT7610U chipset.

As Mediatek had acquired Ralink Technologies, I was hoping that this meant that this would be one of the more favourable adapters to use in Linux. I still have fond memories of the early days of 802.11g when Ralink Technologies RT2500 adapters enjoyed out-of-the-box support (along with the Zydas Technologies ZD1211 and later joined by the Realtek RTL8187B). It seems that support was still good into the 802.11n era, where the Atheros 9k-series (TP-Link TL-WN722N for 2.4Ghz) and Ralink RT3572 (Tenda W522U for dual-band although with terrible sensitivity) had decent out-of-the-box support. Unfortunately, the march of progress has meant that these older chipsets are very much off the market, replaced with newer chipsets mainly from Realtek (e.g. TL-WN722N v2). At the least, this means some compiling of drivers before things work. At the worst, it could be nigh impossible.

Unboxing

The unit comes inside a familiar lime-green cardboard box, loudly proclaiming a three year warranty, high power and 5dBi antenna. The unit is a little different from most, instead of being a plug-in unit, this one is designed as a puck that sits on your desk and is connected by a USB cable. This unit is sold as an AC600 rate unit, meaning a single spatial stream on 2.4Ghz (150Mbit/s 802.11n) and 5Ghz (433Mbit/s 802.11ac).

The rear gives a little bit of information about some of the features, but is otherwise boilerplate text. The sides are not much different, with an image of the adapter, a list of package contents and some basic specs. There is also a QR code that takes you to the product information.

The unit claims support all Windows from XP through to 10, but lists no other operating systems. I wonder if this was a deliberate choice to ensure they can’t be blamed for a lack of Linux or Mac OSX support.

The unit uses a USB 2.0 connection, and is thus likely to use an older chipset. This may help for compatibility, but could also indicate throughput bottleneck as USB 2.0 is only good for 32MB/s (assuming no other devices in an ideal situation) which is around 256Mbit/s.

The underside has the barcode, and it indicates that my unit is Version 1.0.

Inside the outer box is a plain white box. This folds out to reveal the contents.

The parts are placed into a plastic moulded tray, with some items underneath.

All up, there’s quite a few pieces of paper, a full sized driver CD (although the drivers are available online), a USB cable, the adapter and an external antenna.

The adapter itself is quite beautiful with a lot of curves and vent grilles. It almost looks like a space-ship in its shape. The front is glossy and reflective, with the USB port and indicator LED.

The rear has the WPS button and the RP-SMA connector for the antenna. In a rather unfortunate move, it is recessed quite deeply. It’s as if they chose to include the connector to make the adapter more versatile in allowing it to be connected to different antennas, then decided it was too risky to let the user easily switch antennas and so shrouded it making tightening of the retention nut very difficult. Nothing a dremel can’t fix, but this design is not something I hope to see in the future.

The vents stretch top and bottom, with a serial label at the bottom. It seems that this unit is CE marked, which is appropriate for Australia, but it means this adapter is less capable. According to TP-Link, for those using FCC standards, the output power is <30dBm (I presume, this means 30dBm almost precisely). For those in CE countries, the 2.4Ghz output is <20dBm and 5Ghz output is <23dBm (or in other words, similar to most PCIe cards). I feel this is rather disappointing that there is a 10dB output power gap which might be quite important for long distance links. It’s probably nothing that can easily be changed either, as the region coding would be encoded on the EEPROM along with other transmit power correction coefficients, which makes modification difficult.

Regardless, another strange choice seems to be the choice of the orange-and-black colour scheme. While the body of the adapter is a nice matte/glossy black, the feet are orange and stand out like a sore thumb.

This is replicated through the “fin” shaped antenna’s base which is orange coloured.

The supplied USB lead is rather stiff, so that should be a good sign in regards to thickness and shielding. However, I couldn’t find any information printed on the lead itself as to its constitution.

Teardown

Rather surprisingly, for a change, this unit has four small Philips head screws underneath its orange feet holding it together.

Once the screws are removed, the halves can be parted to reveal the rear of the PCB. There is a piece of black plastic in the top left which seems to be used to avoid any light leakage through the grilles on the underside from the activity LED.

The PCB is dated Week 49 of 2016, making it somewhat dated. There is an outline for a shielding can which was not installed – this may compromise its RF performance slightly, but seeing as it claims to be FCC approved, it probably doesn’t have any major EMC emission problems.

As expected, the chipset is the MT7610UN which is a single-stream chipset by design. While this is not optimal for many access points which have two streams, it will at least provide some benefit over 802.11n and work where you only have one decent antenna to use.

To muster up the transmission power, it seems a Skyworks SKY85728-11 5Ghz amplifier is used.

Installation in Windows

If the device is just connected to a computer running Windows 10, there are no compatible drivers for it by default. After downloading and installing the package from their website, the adapter functions as expected.

There are a limited number of advanced options which can be toggled.

The driver itself seems to be made of a complex weave of files and patches. It doesn’t inspire confidence, but the card does work properly even on my AMD Ryzen machine with no BSODs. The same could not be said about the cheap Realtek-based unit.

The device identifies with VID 2357 and PID 010B.

While using it, I found the card provided good consistent connections with a high indicated signal strength. Throughput was good for a single-stream device, but the Realtek based card with two streams did outpace this card somewhat in stronger signal areas. I had no difficulties maintaining connection throughout with either unit, so I’d have to say that I’m fairly happy with this one too (at least, on Windows).

Installation in Linux

While I had assumed that its Ralink Technologies heritage would mean that the MT7610U would work well under Linux out-of-the-box, this was not the case. In fact, it was just as hard to get things to work as the Realtek card I tested earlier. The first problem was hunting for appropriate Linux drivers that would build under my recent 4.14-series kernel. Even if you found one that built, you might have to modify it to include your USB PID/VID. Then you might find (as I did) that the driver complains when loading as the EEPROM data on the card is of a different revision and that crashes the system or causes it not to shut down cleanly.

After a lot of trying, it seems the version of MT7610U driver from xtknight patched for the Linksys AE6000 is the one that builds and works best. It at least let me connect to networks and use it as a regular Wi-Fi station although without signal strength indication. However, it does involve opaque binary blobs and lots of patches. I did try monitor mode, and while it didn’t crash the machine like the Realtek card did, it could not report signal strengths or channel numbers correctly. Channel changes/hopping would not be controlled correctly and it would fail randomly. I didn’t have a chance to try hostapd functionality, but I suspect there could be issues there too.

Conclusion

While it took some effort to find a non-Realtek based modern dual-band 802.11ac USB Wi-Fi adapter, I’m not sure it was worth it. The adapter performed well under Windows, although with its USB 2.0 and single-stream limitations. The signal was fairly strong and the unit was very sensitive. Having the cable allows for better adapter placement, and the external RP-SMA adapter allows for changing antennas although the shroud does interfere with it somewhat. The drivers seemed stable under Windows on my AMD Ryzen based machine, which cannot be said for the Realtek adapter I tried earlier.

However, under Linux, it seems that this card is almost equally as frustrating as the Realtek, being a chase-around for drivers that would build under your kernel and accept whatever quirks and limitations that come about. While it would seem to support monitor mode as well, it is broken, and even basic signal strength reporting seems to be problematic. The use of binary blobs and the lack of chipset manufacturer support in driver development and upkeep is rather unfortunate as well.

It’s rather frustrating that there doesn’t seem to be any dual-band 802.11ac chipset that works out-of-the-box on Linux in a fully-featured and reliable way. This may change in the future, but by then, maybe everyone will be transitioning to 802.11ax. This is likely going to be a frustration for many Linux users, especially those who have no Ethernet handy or are using single-board computers such as the Raspberry Pi who might want multiple dual-band capable interfaces on the one board. I suppose it is fortunate that at least the new Raspberry Pi 3 has an 802.11ac dual-band radio on board.

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