Question: It's been a while since I have soldered, so I bought a cheap unbranded soldering iron to use while I re-familiarised myself with the skill. After a few weeks of use, I turned it on just now and it popped with a blue spark. Now it appears to be dead. Did I do something wrong, or is that simply what happens sometimes when you buy a cheap soldering iron? I'm curious to find out what could have happened.

Ironically, just before the magic smoke escaped from the cheap one, I actually bought a new soldering station (Hakko FX-888D) earlier today, as I had a feeling it was time to get better equipment. Spooky. I guess the cheap one got upset and self-destructed.

Out of curiosity, I dismantled the dead soldering iron and took a photo of the board inside.

[![Dead soldering iron PCB](https://i.stack.imgur.com/JHrz8.jpg)](https://i.stack.imgur.com/JHrz8.jpg)

With my limited knowledge of electronics, my intuition tells me that an arc occurred between the AC wires. If so, is this bad luck, bad soldering, or user error?

[![Close up of the burnt AC wires](https://i.stack.imgur.com/aKqa0.jpg)](https://i.stack.imgur.com/aKqa0.jpg)

The insulation appears burned, but also the core of the wires seems to be a bit frayed. Was this as a result of the arc, or low quality manufacturing?

*Bonus question:* I wasn't touching the button at the time the iron popped, but if I was, would I have received an electric shock? Would it have been life threatening or painful?

*Edit:* I am in the UK (230VAC).

Answer: 
This soldering iron is garbage. The PCB has been soldered by machine and is likely ok. The power cable looks like it hasn't even be soldered on in a factory but by home workers with bad equipment and bad skills. It starts by the cables not being properly deinsulated (you can see a number of torn copper strands) and then not being properly twisted and presoldered (you can see lots of blank copper) and then not being properly shortened: there are far too long open strands off the solder pads. The solder joints look more baked on rather than thoroughly heated, particularly the right one. Also it appears like there has too much been cut from both outer insulation and wire insulation to have any pull protection measure work reliably.

I would expect the ground wire to easily sprout a copper wire over where it may touch the live wire.

But it doesn't even look like that is what happened: one can see in the upper picture that tracks leading to the switch have burnt off, so the short wasn't even in the awful cable soldering (where the damage would have been contained nearby while blowing the fuse) but was somewhere higher.

In addition, the PCB design does not appear to accommodate any significant amount of cross section for the ground tracks, so the amount of security provided by them is limited: you might get a flash and a bang and the thing continues "working" after having rid itself of the ground track. And might even work for the next user after having killed you.
It looks like the mains cord was not fully soldered to the board.
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You can see a stray whisker of the ground still. There were probably also loose strands on the current-carying conductors. They probably flexed enough to touch when you were handling the cord, and when you plugged it in, they bridged a rush of current through and vaporized. POP!

I'm kind of surprised that it broke the iron. It shouldn't have. But whatever. I've been using $10 irons all my life and they work okay for me without any circuit board inside them. But that hakko is super great too, so enjoy it.