Hi Just a quick follow-up video to this web / yeah, Eight Nine, eight D plus Seoul during station that melted down this SMD rework station a link to the previous video if you haven't seen it and we sort of came to the conclusion that it was probably this fan failed because it has actually failed. We can measure that and then maybe something happened to the control loop or or something. It couldn't detect the temperature increase in this and didn't shut off the headon. Now one theory is that okay, the fan blew so there was no air blowing over this element anymore.

And here's the little thermistor in here that measures the temperature and this is a ceramic insulator for the heating element here. And because there was no fair blowing over it anymore, then the thermistor was detected her own temperature and it kept pumping in the power, but it's kind of near enough to still get radiant heat there. It's all covered in metal and everything else. So I don't think that was a real issue.

But anyway, a lot of people in the comments for the previous video said aha, it is the SCO sorry the triack in this thing which is here and and it's a Bt a 16 / 600 volt triac. pretty decent one from St Design for you know, medium power applications. Here's the datasheet and it looks like to be a genuine one, not some knockoff or anything and a lot of people said ah, the triac failed short And sure enough, if the triack actually failed short, then there's nothing that the processor on this thing could actually do via the gate control optocoupler. Here, it couldn't switch it off, which could certainly be a following mode.

A lot of people have said that oh, they've seen other yee-haa / WEP our stations fail because of the triac, but I actually measured the anodes on the triac here and it's not shorted so we'll actually test this in a minute. And it was kind of like too much of a coincidence to me that the fan also fail because I like think of a mechanism that if the triac failed short. yeah, the heating element go up. but how does that really kill the fan? Okay, it could have melted it down, could have melted the coil inside, or sunlight and it broke any connection something like that.

But the fan is like I can't see that happening. And likewise, I It's kind of hard to see how a fan fire would cause a failure in the triac like a short in the triac. I Guess maybe it's possible in some weird scenario. But anyway.

so I've measured the triac and it hasn't failed short. In fact, it seems to work just fine and that's what we're going to have a look at today. We're actually going to test this and spoiler alert. Look, it's working so it's not actually the triac and I've if physically removed the snubber Network down here I've removed the optocoupler Drive and everything.

So I'm just basically connecting up to the leads of the triac in here and this is basically what we've the setup that we've got in Dave CAD which you can download by the way on github I might have to link that in. Down below, you can get the official day of CAD Um, Anyway, got an AC mains transformer that I show you. it's like a nominal six and a half volts or whatever. We've got a 50 ohm load here going into our track of the to anode pins of our track and the gates going off to a pot here that we can control the turn on turn off time for each AC cycle.

And if you're wondering what a triac is, this requires a whole different video qussuk. You can really go down the rabbit hole on these things, but a triac is basically two Scr's back-to-back and an SCR is a silicon controlled rectifier also known as a thyristor. But once again, you can if you want to go down the rabbit hole and it's I restore an SCR technically aren't the same thing, but you know, for most purposes you can say an SCR is a theorist and vice versa. And you can say that a triac is a bi-directional thyristor as well.

So you'll see a lot of these terms interchange. People say thyristor in when they mean SCR a vice-versa Or they might say a bi-directional fiery stir when they really mean, you know, when it's actually a triac and all that sort of stuff. The terms for these things are actually rather confusing, but basically to Scr's back-to-back like this and an SCR is basically a diet like this with a gate. so just look at one SCO like this and I just go over very crudely how it works.

It's basically, as the name suggests, it's a silicon controlled rectifier, so it's basically a diode like this that allows current to pass through, but only when you get enough gate current in here. And these aren't voltage operational devices. they're actually current. so you need a minimum gate current to flow in here and then it latches on.

It works like a latch, and once you provide that gate current, you can actually have a switch in here like going up to the positive thing and you can provide that gate current through there and this SCR will actually latch on so you can just a momentary button switch. you can press there and it'll latch on this SCR and the SCR won't turn off until such time as the holding current through here depends on the load and everything else. but when you, it'll keep maintaining that latch position until a minimum holding current where it'll actually just unlatch and then you can restart it again so quickly. In a bit more detail, how an SCR works and hence how a triac works cuz the tracks just to Scr's back to back works on a see we've got the equivalent circuit in this case for a trike, it's working in one what's called one quadrant of the Tri.

But just think of this is the equivalent circuit for the SCR I Just got this from Wikipedia here and basically to a regular bipolar transistor regular bipolar transistors PNP and NPN and hopefully you can see that. so the base current just flows through here like a normal NPN transistor like that. and once you provide enough gate current of course, then current starts to flow through the NPN transistor. Basic, you know, transistor operation and then of course because you've got the PNP up here, it can conduct through its base like that and you know It's a bit confusing that we've got bases here when we're talking about NPN transistors, n gates when we're talking about thyristors not to be confused with gates on mosfets which are voltage you know driven devices, this is still current driven so it ends up flowing through like that.

but once it does that, of course it switches on this PNP transistor so that some current can now flow through here into the base to keep this thing switched on. So it latches on with this PNP transistor like this, so you only need to provide a little short burst of gas current in here to latch this since this to transistor circuit on and that's what an SCR does. It actually latches on and I'm sure I've done a video way way back on SCR latch up which is a phenomenon in semiconductor structures inside. ICS like a regular logic ICS where they will act as an SCR and they'll latch up a similar sort of you know a thing happens with the output structure of transistors in logic circuits.

I'll link that in at the end up here somewhere. Check it out. Anyway, that's how an SCR works and latches on. and you can see that in this case, when the polarity reverses in an AC configuration, the current can't flow through here anymore.

So one SCR inside the Joule back-to-back triac and it switches off and then the other one can start to conduct in the opposite direction. Hopefully that makes sense. So they're very cool devices. Scrn Triax and as I said, a very big deep rabbit hole if you want to go into the dynamic operation of these sorts of things and it really gets a bit complicated.

And the thing about a triack is when you have two of these back-to-back in Reverse orientation like this, you can use them for AC stuff. and that's why heaters like this. So just imagine this is the heater here connected up to your 240 volt mains here a triac. You can actually control the on and off cycles of that and every time that the AC waveform swats polarity like that, you can actually it.

You get the minimum hold off a drops below the minimum, hold off current and it switches on and off. So you can actually by adjusting the current going there through to the gate pin here on both cycles. That's why on a try with AC you have it connected across the AC source. Like this, you can actually vary the on an off duty cycle and you can control your load.

So this is useful for all sorts of you know, dimming applications. for lamps. for motor control and heating elements, you can vary the amount of power that goes to it. So let's have a look at the setup we've got here very quickly.

I Went through all the details but I've got a little AC transformer here that I built when I was like I don't know I was 10 or something when I built that. it's actually very very old and it's just got a mains transformer in there and I can select the different taps I will just use the minimum 6.3 volts ac and I'm using two decade resistance boxes here just to simulate the upper half and the lower half to that because I just didn't bother with a pot. so use those two and I've got the scope. The ground is actually up here because it's floating I can do that? beware.

I've done a whole video on how not to blow up your oscilloscope and channel one which we'll see which is the yellow waveform is measuring the voltage across the load resistor here which is essentially the current flowing through the triac like this and the channel two which is green waveform is just the AC input signal which we're triggering off So as you can see tonight. so as you can see, it works a treat. So this is the input AC signal that we're actually triggering off and this is the current through the trike and you can see that our duty cycle is like you know it's somewhere in the middle and if I just these resistors Here we can see that Judy cycle actually change like that. So we can actually control the turn on and turn off time of this triac so it seems to work and you can actually just see a little current pulse in there when it actually switches.

There you go, you're that neat. But anyway, doesn't seem to be anything wrong with this trike. Yes, it could certainly fail at like high voltage. There could be some you know high voltage related issue that we don't know about, but it definitely hasn't failed short.

and it does actually work as a triac. So in this particular case, yeah, that's not the fire mode. So I did my money's still kind of on that the fan failed and then something to do with the algorithm inside this thing or the measurement or whatever it just it couldn't cope or whatever I don't know and it's melted down. but a lot of people have actually reported similar units from a Hera What? not actually melting down as well? I'm just yeah.

completely going like white-hot just like this one. David's one here and it's melting down so they just tossed it in the bins so well. what fell, Something fell, something in the lab fell down. oops, any happens.

Anyway, so there you go. We've got some sort of failure mode there. The triack is okay and a basic testing by the way. I Did actually try to measure the triac with my little M tester here which does actually measure.

try X but it couldn't do it because this only I believe this only gives out like a couple of milliamps gate current affair. Milliamps test current. so that's not enough current to actually turn on this particular triac here. This one I think needs 10 or 50 milliamps depending on what particular art part it is or whatnot.

So yeah, this as cool as these little and this is capable of testing. Triax By the way, you can like it has a I don't have another one here but it can show. it can show up with like the triac symbol and everything else so it can do it. but it can't do it.

Unfortunately if you've got a triac that needs more than the base current the base current gate current. it's not an NPN rubbish to the Troyer gate current required. So yeah in this case just doesn't have the juice required. And for those who want to see the little blower fin here, I've just taken the top cover off here and it 24 volts.

It certainly doesn't work. It's cactus here we go. Bonus Teardown: If you haven't seen it, it's got the four coils with the permanent magnets around there and then inside there. Just got the ring of permanent magnets so that they can control the magnetic field and make that the wall alternate the magnetic field in a circular fashion and make the motor spin.

And there it is. I Had to pry that out of the back of the case and it is ridiculously simplistic. Yes, there's it's. nothing in there except oh, there's one cap that is that a cap.

looks like this one cap there and what else? Then we just got our driver. I See up there, can we get a number on that? It's going to be some weird thing you probably can't get a datasheet on I'm sure. there you go. What do you know? you can't get a datasheet for this thing? This is actually pretty cool BCD But I Got it from Diodes inks I Guess they were bought by dieting and it's an on-chip Hall sensor as well, which of course are you know to know the position of the thing.

Um, it's really cool. I Like it. it's for dual coil brushless. DC Motor brushless DC Fan revolution counting speed measurement all that sort of stuff.

So it's got an on-board driver. That's it. Fairly crude, but cool device in that it has a and there's the magnet. you know you've got to mount it in the right orientation.

of course. trap for young players if you're using the Hall effect sensor in it. And there's the magnetic flux density curves for all you magnetic aficionados. And that's all.

There is like two coils now, so they must have opposite side coils as two coils So that's how they're configuring this. Neat. And of course, for this low cost fan, they went. oh, we don't need this diode.

Rubbish. We don't need this. RC these are C Fielder's down here on that now. don't worry about that, she'll be right.

just hook it up to the coil. Bob's your uncle so that's just crazy simplistic. I once. I've seen before.

a much more complicated than that in terms of our all the drive. but I guess okay, just do it in one chip. it's you know, ultra low-cost But anyway, that puppy has failed. and whether or not it's the, if that was the cause of the issue or whether or not I don't know something else went wrong on the board and killed it.

I I don't know I Think it's just likely to have like just failed somehow, just mechanically or electrically failed anyway. I hope you found that video useful. And please let us know in the comments what you think about. You know how this thing failed or whatever.

Hope you liked it if you did, give it a big thumbs up. As always, discuss down below in the even comments: youtube comments or Eevblog forum Catch you next time.