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too much bang for buck

Posted under Other Technology at . Last updated 2019-08-23 22:52.
Tags:hardware, soldering, failures, WEP, Hakko, TAIKD


blown fuse

Some time ago I needed a new soldering iron. And a heat gun would be handy, but I had little cash spare. Soldering stations with temperature readouts seem to be the thing now, and I can see the attraction. My interim solution was a WEP 852D+ 2-in-1 iron / heat gun. (Which may be a rebranded something else, not sure.) I prefer a more modular approach to tools, but, well. Worst case, I thought, it would do as a heat gun with a fallback iron, and I’d pick up a primary soldering station at some point. Initially, all was well, and I’ve been doing a few essential jobs with it while life beyond electronics gets sorted.

A few weeks ago during my last bout of repairs, the soldering iron handle began to loosen every time it warmed up, eventually falling apart in the hand in the middle of a job. Lacking time to do anything about this, the only immediate solution was to tighten it manually.

But rather than retightening the handle, this turned the iron against itself, twisting the wires together inside. Eventually they shorted. So it wasn’t just loosening due to expansion — it was slipping whole turns of its thread.

(On investigation, the only way of fixing it safely would be to let it cool down, remove the tip, tighten handle carefully not twisting the little PCB, and refit tip — but then it would come loose again with heat . . . )

The iron cooled down and started to smoke in the middle of a delicate operation I had too few fingers for anyway.

This could have meant having to replace the iron. Should, even.

Actually the display went dead, the hot air gun started itself up while in its stand, and some little popping noises were heard from the case. I switched both sides off and holstered the iron while I tried to rescue the work, scrabbling in a drawer for my little old unregulated iron, trying to hold the piece together with the other hand. By the time I turned back, the WEP case had begun to emit smoke, even though off. Then it uttered a loud bang, like a small electrolytic had exploded, and a smell of roasted electronics filled the room.

I unplugged, opened the window wide, and tried to complete the job with the underpowered tip. Nope. Eventually I had to dig out a thirty year-old pyrography iron, which at least had the watts. If I hadn’t already found it a few weeks earlier I’d have been back to blowtorch and copper block. Which really is not how you want to solder leads in switch-mode power supplies. In a hurry.

(I know. Hurry. There’s your problem.)

Later, I opened the WEP case. There is surprisingly little inside it, and little of that constitutes overcurrent protection devices; beyond the internal mains fuse, which was what made the noise. It fused because the wiring in the transformer had finally shorted, after melting, because even with both output devices off and the control circuits dead, current was still flowing through the short in the iron.

burnt-out transformer close-up

To be more explicit:

  • The soldering iron does not have any independent overcurrent protection; nor does the heat gun.
  • The front panel switch does not isolate the soldering iron. You wouldn’t necessarily expect the heat gun to be isolated by its switch because it always has to cool itself down with the fan even if you switch off. But an iron radiates.
  • The PCB includes two MOC3041 optoisolators, but it’s gone anyway; in fact the solder on two of the board traces by the iron connector terminals has melted. Without wanting to spend too much time on it, it looks like the optoisolators protect a 20-pin DIP chip (though not from its power supply).
  • The only overcurrent protection for anything else is that 6A glass cartridge fuse. Suppose I’m grateful for that much — but 6A for a soldering iron? (You could run a small welder on that . . . ) Ah, no, no — 6A for a heat gun. Now maybe that should make us stop and think, when we’re designing devices . . . ?
  • Oh, and there are three power resistors (1W) on the board, one of which is actually touching a capacitor.

In summary, this is ridiculous. There isn’t even a true power switch on the unit; it can only be powered down at the wall. (Of course, I knew that already, only not the depth of the lack.)

And incidentally, about two thirds of this large case is empty, with a PCB at one end and a transformer at the other. Space for protective devices was not the issue.

open, mostly empty space
the emptiness inside


The unit was cheap, but this is poor at the price. Total usage time: about 18 hours. Lifetime running cost: about £3 per hour not including power. Condition: dead. Maybe I’ll use the case for something.

Onwards and, um, Altitude To Be Determined

Replacement step 1 is a Hakko FX-888D soldering station. Any better?

Looking at it on arrival, at least it has a power switch. It’s very nice in the hand. A soldering station doesn’t need to be nice in the hand, just the iron. I like the iron connector, too. No awkward screwing in; just a DIN. I’m not so keen on the two-button interface, which as well as providing a less-than-intuitive temperature control, apparently has a password function I hope to ignore. (Why password? Just because we can? If you have security issues with your soldering station it might be best to get one that can’t easily be hidden in a pocket?) And . . . no screw-in fuseholder anywhere. Right.

Opening it to look for protective devices isn’t straightforward as the case screws are under the rubber feet, which are glued in. But once opened, it’s rather nice inside too. Only, its fuse is a soldered-tail 0·63A thing, which I don’t have a spare for, and is less than convenient. (The one place you don’t want to ever have to solder a fuse is in your soldering station, right?) It has a MOV with it, so that’s something. Main thing is, it doesn’t need to isolate different sections, so it can get away with simplicity. And the more main thing is, the iron handle is solid enough that I can’t pull it apart, even warmed up. Whatever kills this, I don’t think it’ll be thread slippage.

I see the FX-888D can be used with a Hakko N2 gas shrouding system. I’ve never tried gas-soldering rather than -welding. Peg that thought.

But now no heat gun. (And I’d just got used to not using lighters for heatshrink.) What reasonable soldering heat guns are there out there? Weirdly, availability of good quality ones seems to be limited; I can’t really tell much difference between those I’m seeing; all rebrands? How good does a heat gun need to be?

Eventually I found something slightly different, a TAIKD TK-878. Really the most significant difference from the others is that it clearly has a C-14 power input socket; not much to go on, but maybe preferable. And how’s its overload protection? Should have a 4A fuse according to spec, accessible externally? Yes. This is also slightly nice in the hand. Maybe the front panel is a bit plasticky for my taste but it’s probably as robust as it needs to be.

My one serious criticism is that it was supplied with a Schuko-plug cable (I knew that in advance, not a problem) with another of those abysmal unfused BS1363 adaptors. But I assume that’s the distributor, not TAIKD. Binned.

Must admit I thought it wasn’t working at first, as it took a while to wake up and smoked a bit (no factory-test/burn-in?). But it improved, and once you get the idea that the fan is activated by angle to the vertical it becomes fairly controllable, though you can’t really use it pointing up at something from below. And its switch is an actual power switch, so leave on until cool. Good.

TAIKD TK-878 and Hakko FX-888D

We’ll see how far we get with them. Absence of further critique implies acceptability.

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