During a recent live stream, I had a bit of a technical instant. I was demonstrating a high voltage igniter which has a little sub probe and when you slide up, the the tips slide out of the metal casing and then it generates a spark across the tip. Let me show you what the spark looks like if it shows up, is it showing the slight spark across the tip there? and while I was doing it, I was waving about some photos. I'll do it with this one as well and you might be able to hear it. Did you hear that swishy noise? and that's because that the arc? the ionized air has been moved out the way and it was re-established and archuge time. That made quite a distinct noise and a pattern as it moved and then it suddenly stopped working when it turned on this green. LED just lit and that was it. Can you see that green LED Let's Zoom down in this little bit. So I shall move this into the middle of the circuitry and when you push the button, nothing happens. Uh, that's with the switch off. When you put the switch on the green, LED gets brighter and again nothing happens. It's quite hard to switch thing so I thought well let's diagnose this and see if we can work out what went wrong. I Have a theory that it's arced onto the metal casing and found a route back to the circuitry via the USB port. So that's an area of high suspicion. The one component I can't really fix here is going to be the microcontroller if it's blowing that. But let's get the Uh drawing in I'll just grab the drawing now one moment please. I say drawing I should have really said zoomed in picture of the circuit board. So let's explore this. We have the microcontroller. We have the charge port. We have this switch. We've got a little charge control chip in Lth7 and then we've got a mosfet driving the output coil which is across the output here and that covers across to our secondary which produces the high voltage spark. When you slide the thing forward, it pushes this little switch in that signals back to the microcontroller. here. that is about all. there is to see a couple of LEDs, one of which is the Rogue one that is staying on, but that suggests that this is powered. Which is quite odd because the circuitry is very strange. I should just take the hands out the way if you want to take a snapshot of that and have a go at reverse engineer it yourself. But here is the schematic. This will make more sense of things. although one bit did not make much sense. Two bits did not make much sense. That's okay, it's educational. I shall Zoom down This here's a USB charge port and it charges the Lithium cell here via an Lth or some very classic circuitry. It's got a 3K resistor to set the charge current and it will switch off at 4.2 volts the battery, then Powers the Lithium cell Powers all the rest of the circuitry, but for isolation, it's got a switch that will switch off the microcontroller so it doesn't provide a signal, just presumably as a safety internal. Also, to save power, and uh, when you switch it on, there's a decoupling capacitor, a 10 Ohm resistor for filtering, and another decoupling capacitor, and then the microcontroller itself. Oddly, and this is very strange, took me a while to work this out. There's a mosfet across the switch and it's uh, it's an N Channel mosfet, which means it's normally designed to switch down to the zero volt rail, but they've got to connect to the positive rail and when you plug the charger in, it's the charge input. The 5 volts goes straight to the mosfet, which makes this a prime suspect and turns on and effectively bypasses the switch. What that means is that because the microcontroller is doing the charge indication, that's LEDs it means it Powers up and it detects a signal from the charge chip and then does it. You know it's charged or not charged and at the moment it's showing that it is the green light and I think it indicates it's charged even though it's not charging and that makes me wonder if the either the Lth7 is failed or this mosfets field when you push the button in. And here's the button here. there's a little pull up resistor it drives these transistors. This is where it gets very messy. Usually on something like this, the microcontroller might drive the mosfet directly, but because it's a very low impedance coil, it's a tiny little Transformer In this, it's probably going to have to switch at a very high speed to get a decent Rising Spike to get a good spark. Often in these things, for ignators, they'll have a high voltage coil that will basically have a capacitor in Sears with it and charge up the capacitor and then it will shunt it suddenly with a thyristor or sideak and that will create a high current pulse. But in this instance, they're driving it directly with a mosfet. It's possible that inside here, particularly because the wires are very close to the high voltage output, it's possible that that's where one of the connections has gone on to the set of wire and found to switch to the ground in this circuit and the other one has found its way back as far as I'm concerned, possibly via the USB port, but in this case, they want that fast switch on. now. most vets have a capacitance on their gate, so you can. If you want to switch them on off very quickly, you need to use a special driver that can quickly charge and discharge that to get a very fast transition. and I Initially thought this was a PNP transistor to the positive reel and an npn to the negative reel. and it was A by connecting both the bases together, it was actually alternating between them to give that very high current. Drive Make sure that it charge and discharge. It turned it on really fast in reality. Uh, this is all art for elbow. as we see in the UK There's a Npn resistor connect to the poster. we own the PNP transistor connect to the negative reel. Both images are connected together and it's what's called a totem pole driver That makes sense. There are totem pole drivers shown for driving mosfets. Kind of an old-fashioned circuit. Very strange. Um, but there's a pull down resistor here to bring that into a known State when it's uh, not in use. which is going to be a slight current draw. No, it wouldn't because uh, yes, it will because there is going to be a slight current flow through these transistors. But even when it's turned off, but um, that brings it into a known State. And likewise, the mosfet is also dragged into a known State when it's not being powered. There is an option for a little tiny capacitor to be connected across the coil, maybe to protect the mosfet, but they've not included that. Maybe they felt it wasn't needed, Maybe they didn't care. So here's my first suspect: If the mosfet is field, it might be bridging and leaking current through to bring on the microcontroller, because even the switch off current is getting to making control and the only ways I can see it actually getting there. Our potentially it could be one of these transistors, but I'm suspecting that the mosfet is first in line because if you look at the original drawing, it really is. If that's the positive pin of the charge socket, it goes straight to the gate of the mosfet. but it also goes over to the Lth7 that if this has been the issue, then that is where it's like to be. So let's explore. let's experiment with that. Oh, did I mention yeah, the rest of the circuitry sorry I'll finish the job. It detects when power is being applied to the maker controller by this pin being taken uh, or from this voltage tab being taken to the main controller. and also it detects the Lth7 end of charge signal over here, which goes over to this connection. It's a very strange circuit, let's bring it in. So the first thing that comes to mind is just absolutely just taking a pair of snips, right? So at the moment, uh, I'll turn that off I'll Power It Up in the green light lights. Okay, so it's still got that fault I'm going to Lop that transistor off I could get the soldier iron on I could hit it up or I could be brute force and just chop this off. Is this a bad idea? It's a terrible idea. It's a terrible idea? but it is done. It's off. We have lifted the track. They're not sure. uh, is that going to fix it? Yes, right? or I've completely destroyed it. So if I switch this on now, it's showing green and there's a spark. So what's that mosfet? It's not actually giving a very consistent spark because it's being powerful, the power supply and the current is quite High Uh right. Tell you what. I'm going to put the battery back on this and we'll try it again one moment please and it's fixed perfect. The only difference is that now when I want to put it on charge, I'm going to have to make sure this switch is turned to the on position because that's the one where it can actually the makeup processor is active in consensus, although it will still be charging the background properly. Uh, it's working now now. Note that this is very high frequency noise. If you don't like high frequency noise, remove your headphones or turn your speakers down Now because I'm about to put this next megaphone ready. Very hissy high frequency noise. If you want to see the spark, I'll just zoom down like this and I shall Shield it from the light and you can see the nice purple spark arcing across the end. There are little whiffs of ozone in the air, so let me show you in the schematic what was happening here Though it's a very odd fault. it was the maker control that was misinterpreting what was going on. Uh, while this was effectively in a fault state, so I'll just make sure I'm focused down onto. there. Here is the mosfet that filled and it was basically bypassing that switch and permanently powering the microcontroller, the microcontroller. It may have been potentially putting a signal a bit of current back there as well to the input the Lth07, which meant that the microcontroller would potentially be able to interpret this as an active charging signal, but because Lth7 was basically getting the same its output was connected its input. It was somehow duping the microcontroller into thinking it was charged and it was just displaying the green LED And that was it. So what I did there was I Removed this smart thing violently and now when you plug it into the USB all that will happen is that if this switch is off, the power will be applied to the Lth07 and it'll be charging the background until it reaches 4.2 volts. They're not cut off, but if the switch is on, the microcontroller will be active and it will be able to actually indicate the charging State on these two. LEDs And that is it one. 10 little filled mosfets. Mosfets are just a very prone to damage by electrostatic discharge, But having said that, I'm not sure that this is this would be a fair trial for a mosfet, particularly given that this went to the gate which is not a great result for mosfets, but that is it fixed and now things are back to normal so this can be used to do what it was originally being used for lighting the wiffles. You may have seen the wiffles in the live streams uh, it's just little mini fireballs and they recently started being lit by this until I burst it but now it is fixed.