This circuit board was sent for our perusal a while ago by michael he'd had it in a light and it failed, and it did that usual thing - that the leds all crack and burn out. But it's quite an interesting circuit board and i'll show you the enlarged form of this, since i have not had to take anything apart, it's all ready for photography. So, let's zoom in on this and we'll take a look at the circuitry. We have the incoming supply.

We have two 10 ohm resistors to limit the inrush current. We have a tiny little surface, mount metal oxide varistable, it says vr1, then a bridge rectifier converts the ac into dc and then the option and pads for another metal oxide varistor and then the leds are actually current limited by one two: three uh bp5136h drivers - and This is a typical circuit used with these, but it's not using a typical circuit. Normally you'd have the leds divided into four sections and as the voltage of the sine wave rose up and down, it would initially light the first section and once the current threshold was reached, then like the second and then the third. So as the voltage went up and down, it would like progressive numbers of leds, and it keeps a strange if you look at it through a camera, it sometimes gives us a flickering effect.

I can't do that with this one because uh it's dead, that's why i can't do it. But, interestingly, here for the final stage, they've actually got two 2k resistors 4k in total across that it's quite unusual and they've done that separately to each and every chip. But then commoned all these parallel connections up also, this is a resistor that sets the current by the current sense. So the current flows through the leds goes through the current sense, resistor and uh.

It will regulate the overall current in the circuit, but uh. There is some extra circuitry in this one and it's based around a couple of transistors here that seem to switch in other resistors. The reason there's so many links uh. It looks a busy circuit board, it's not as busy as it looks.

There are tons of links because these chips are effectively commoned with uh three separate circuits driving these leds. But there's a couple of transistors here and i without actually trying the circuit board because it can't because it's dead, uh, i'm going to make a wild guess. Given the circuitry around that it's quite hard to trace out, because it is a aluminium core pcb more about that later, which stops you shining light from the back. But it also has the white solder resist, which makes it very hard tracing the tracks out, particularly when it's a bit grubby and close together like this, but i think these transistors are effectively act as a toggle and might be allowing that function.

You can turn the light on dolphin or change different intensities, not really sure, but what we're interested in right now is what's going on here with these burnt leds, because this is so common in these things, and this is why uh the fact that there's an aluminum Substrate is a bit of an issue so, as happens, you can see damage in other leds here, as happens leds they've baked them now. Are these the hard ones? Are these the soft gel or where are they soft gel? That's gone hard. Now it's pretty hard, uh phosphor loaded sort of resin. Maybe it was gel, i'm not really sure it's hard now.

What can happen is cracks can happen in that and the thermal expansion and contraction and the cycling basically causes a the circuitry that dies inside the bonds to snap off, and you end up with an open circuit when you get an open circuit, because these operate with Quite a high voltage and the open circuit is that high voltage across it you end up this burning a tracking arc, and this is a really major issue with the aluminium substrates pcbs and the reason for that. I shall show you this. This is a standard piece of circuit board material, it's a solid piece of fiberglass and then it's got a thin shim of copper on the surface and to make the circuit board. They photographically transfer an image onto this and then they develop it and then etch off with ferric chloride or copper chloride, and that removes the unwanted copper and just leaves the tracks where they're needed and then there's a lot of other processes.

Drilling and printing. The silk screen and soda resistant things like that, but with the aluminium core pcbs, it's slightly different, the main bulk of the core is a piece of aluminium and the reason for this is for heat dissipation, but on that aluminum then, is a super wafer thin piece Of the fiberglass and then the copper, but the downside of this is that quite often when these fail, i don't know if this one's done it they don't all do it. Let me grab a meter and we'll try. Although, to be honest, i should be testing this at high voltage to get an accurate result here, but if i scrunch my leads through there, i might possibly find.

I don't know that the uh that it's perforated right through to the um, oh very crispy, right through to the uh aluminium as i've found in other ones, and when that happens, i think i need to do a high voltage test on this because uh it will Have broken down the fiberglass underneath, but it's not it's not testing through with a low voltage test, but when it does burn through and there is a fairly common problem, you end up with a dead light and it starts conducting onto the back plate and because uh, Some of these lights are not earthed properly. The wire there's an earth wire into the light, but it's not actually connected to anything. It's just floating thin air. I don't know why they do this, it's very common for the grey imports but uh.

The other issue is this bridge rectifier here, because the current leakage to the aluminium plates in the back or aluminum, if you so prefer, will have a dc bias, and this is where the rcds that would theoretically pick up that leakage um, because this will be current. Limiting so it won't, it won't just go bang and trip the circuit breaker. There will be current limiting through the circuitry here, but uh. The risk is that, even if there's an rcd that you'd think would normally pick that up or gfci the majority of them used in place.

America and britain are type ac circuit, breaker rcds, which are really only designed to detect a sinusoidal leakage like say, for instance, basically the power outside here before it actually reaches here like if the cable got pinched or watched get into the junction box. But when it goes through this, you have a situation where you need a specialist type of rcd to pick that up and germany is way ahead of the pack for ages. They've not allowed ac circuit breakers because they obviously saw the electronics, the progress of electronic stuff happening and all their houses are protected by type, a or b circuit breakers, which can detect the choppy dc in these or smooth dc from from, say something like a car Charger or in the case of the high frequency power supplies they can detect the noise, the high frequency switching output, which can often be defeating. It can often defeat standard circuit breakers.

So this is an issue. It means that you really have to ground these flood lights and make sure that there is connection between the earth wire and the case, give it a good decent test, ideally a pat test. I current that any continuity test is going to be better than nothing in this particular situation um, and it means that really, as time goes on, maybe britain and america are dragging their heels and they need to update and start enforcing the use that all new rcds And distribution boards need to actually be the modern, slightly more sophisticated type that could detect all the other fault scenarios other than just like damaged wiring, so um. That is really the way things are going.

I've come across so many of these that they have leaked onto the case, and people are reporting that they're getting shocks off uh fittings when they go and check why they're not working and they touch them and get a zap because uh it is leaking onto the Aluminium and unfortunately, because either they've not earthed it or grounded it, or it's got that that missing wire. It provides an alternative path of current and that's through them. So uh, yes, maybe the uh iet in the uk, which is our electrical sort of regulatory body, the ones that actually makes up the regulations. Maybe they should actually look at enforcing the progress towards type b circuit breakers, uh rcd, gfci type circuit breakers to detect.

The progressive number of faults like this are going to be increasingly happening in the future.