Fixing a faulty LSPA7 smart plug (XiangHeWang)

This seems to be a very common WiFi smart plug with multi-country socket options. As with most of these things it has its weaknesses, and this one has failed.

The fix is simple enough, but you must be aware that these units are not held together with screws, so the case will never be as strong as it was before the fix, and there is a risk of exposing live connections if it comes apart while being unplugged.

This circuit is ALL live at mains voltage when powered, so take suitable precautions when testing it while open. Complacency is your worst enemy here, and it's not uncommon for people to slip up and grab it to pull things like this out of the socket/receptacle while they're still powered. That results in a very harsh safety lesson.
At no point did I handle this unit directly while it was live.

For the repair you will need a beefy soldering iron for those pesky high thermal mass power pins and tracks. Or just take your time and allow the soldering iron to recover between each use.

If the solder refuses to suck out of the capacitor holes then you can resort to the toothpick technique to clean them. Get a very sharp wooden toothpick, melt the solder and shove the toothpick into the hole to displace the solder. Once cooled, the toothpick will come out easily leaving room for the leads of the new capacitor.

Double check the orientation of the capacitor, as electrolytics are a polarised component and may pressurise and pop if installed the wrong way round. If that happens then just stick another in the right way round after cleaning any explosion-residue off the PCB.

I'd expect the capacitor value to be the same for other countries - 470uF 10V. It's important to use one rated for high frequency use, sometimes referred to as low ESR. (Low Equivalent Series Resistance). The one I used was from a UK component supplier called CPC (Farnell) and had the stock code CA08306. Try to use a proper component supplier, as eBay sells off-spec factory reject junk.

Although apparently rated for 16A, I would never trust such a tiny relay with that current. 5A would be a much safer rating. That means it's fine for most loads, but not things like big heaters.
It should not be used with loads that have huge inrush current, as they may cause the contacts to weld. That means the current spike causes the contacts to stick together. They can sometimes be released with a sharp tap on a hard surface.

The power monitoring facility was a nice surprise for such a compact unit. It uses a dedicated BL0937 chip that is designed for that function.

For the firmware reflashing posse - the chip is marked Beken BK7231T0N32
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