It's not often that I get excited about a fault, but this one was particularly interesting. This is a Dixel Xw7 Okay, Refrigeration Controller: It's like those little program balls like these. these little programmable temperature displays you get that have ridiculously huge menus. except this one has the menu system from hell because it is designed for controlling.

It's just multiple things in refrigeration, so it's got a deep menu with a remote programming console for that. However, this one let me just put the lid out the way. This one had a super interesting fault so it just wasn't working at all. And when I opened it up, it was really obvious what the fault was.

I've changed this capacitor. This electrolytic capacitor had domed. You can see the bulging there. Uh, it's a glan capacitor which doesn't really have much of a history to be honest.

Uh, and someone choosing what I would call an off-branded capacitor has basically condemned a good quality controller to failure. But the interesting bit is that when I opened it up, this transistor here was getting really hot. and I mean over 100 degrees Celsius hot, which is rated up to 150 degrees Celsius but that you don't really want to run them that hot I Was thinking, why would failure of this capacitor, this purse black capacitor affect that Now, if we look at the power supply itself, we've got a traditional Transformer we've got a bridge rectifier down there, and then we've got the smoothing capacitor and from there we've got a 7805 regulator provides 5 volts to the logic circuitry but also the unregulated supply. Powers These big chunky relays for switching High loads like Heating and compressors and stuff like that and fans.

and these other relays are for auxiliary loads like solenoid valves and uh, alarms and things like that. Uh, the unit is notable for having a interface a two-wire interface to a remote display and that is the complexity of what happened here and why that transistor was getting really hot. So let's take a look at the relevant parts of circuitry for obvious reasons: I'm not going to reverse engineer the whole thing because it's a monster. Let's focus down onto this uh to put things into perspective, that is the back, the circuit board covered in tracks and the other side is absolutely plastered in options.

so it's very hard tracing things from either side of the circuit board because uh, the the tracks literally just jump out some forwards all the time and go other under components. However, let's take a look at this why it field and what that Nikon effect was. So the incoming Supply to this goes to the Transformer and it does so via this little blue component down here. CB blue component that is a PTC thermistor and it's designed that if the Transformers overloaded or fails in some way, it will just basically break the circuit in a controlled manner, but it can recover afterwards it can reset.

I've used them built into Transformers in the past and my Fairground controllers because it just protected against those little accidents that happens when people drop in neutral or swap a neutral of the phase. That's probably what it's for. It's basically a self-resetting system that detects that high current and shuts the Transformer down for protection. but the output of that is AC.

Let me just draw a C. So here's a zero voltage line and here is the AC sine wave right and it goes through this bridge rectifier and when it goes should be direct far. It gets rectified into a series of positive going humps and then because there's a big capacity after the reservoir capacitor, it averages out round about there with what's called Ripple on top. Now the Ripple is an important bit because the Ripple is the current that's flowing in and out of a capacitor.

You'll see you have a ripple current rating and normally capacitor is running at. In this case, the Ripple frequency is just 100 or 120 hertz. It's basically the main frequency times two. um, 50 or 60 Hertz times two.

and normally these capacitors last forever. I Mean it's not even near anything particularly hot. It's not like right up against the heatsink. I mean this: Transformer will get worm.

The regulator might get a bit warm. Really, it's not going to get that warm. it is. You know it's fine.

It's not really going to suffer a lot of heat, but what normally happens in Switchwood power supplies, the ones that are operating at very high frequencies. These capacitors do get roasted because the riffle happens at tens of thousands of times a second and they burn out quite quickly. You know those capacitors have to be special. Low resistance low ESR equivalent series resistance.

Uh, otherwise they'd fail really quickly. This one can be a standard capacitor and I've got equipment from the 1980s arcade games with original electrolytic capacitors that are still fine because they are not stressed in equipment like that. So it's really odd. this one has failed.

I Get the feeling: Uh, all I could find out about Glan was that they were a company that originally specialized in photo flash capacitors, but decided to get into the other markets and offered a cheaper product. That's maybe what happened here and it's obvious that the formula was not good. And uh, it's caused outgassing and it's caused this basically built up of pressure little bubbles inside in the electrodes that is vented over time. They'll actually like these, feel unusually light, as if there's nothing in them when I stick them into a component test.

Well, I can show you that Right now, let's bring in a little component tester. These component testers are great. These are little things are just like one of the best things ever for diagnosing components. But if I stick this photo capacitor in, say, between here and here doesn't really matter which pins are put on and then I press the button to wake up.

It's going to say it thinks it's it's thinking about it's thinking about it. it says I think it's a diode with a value of zero nanofarad. It is misinterpreted as a diode because it is so gone. and on the capacitance tester, it just came up vaguely as about Eight Microfarad.

It's screwed it, the electrolyte has dried out. But here's the interesting bit you see: there's a current limited Supply based around that Bd442g transistor and uh, it's got a it's a PNP transistor so it creates a current limited positive Supply And what we have here is a Zener Diode which sets with a resistor that sets a voltage on the base of that transistor and then it measures the voltage across this resistor. Depending the current and about 140 milliamps, it gets close to the threshold that this transistor can turn on and the transistor starts turning off. So basically speaking, if you were to shunt this out, it goes to 140 milliamps and then the resistor will just temporarily dissipate heat.

That's what should have happened. No bit of that. Then goes to what I think is a Zener Diode. It's basically stuffed right in there.

a little tiny diode and capacitor. Um, and that may just be to crop the peak voltage. possibly I was getting quite a high voltage than output of this one, but then most interestingly is a transistor because this goes to a remote display with some segment LED displays and buttons on it for programming the modes. I've not got one of those displays.

It's been quite useful to have one, but to be able to communicate just using two wires. It does a quite clever thing. It shunts the power rail. So there's this transistor.

here. It's that little tiny transistor there, and it basically shunts that current limited. Supply And uh, the remote display reads that as it. it maintains its power supply most of the time.

but when it sees it glitching off, it's got a capacitor that holds a reservoir to keep it running, but it can read that data that's coming across the two wires. And likewise, when the unit wants to communicate back, it glitches its own power supplier that shunts it out, and that can be detected by the receive circuitry going to the microcontroller. But what's happened here is because this capacitorative field, the processor has failed to boot up, and by default, for some reason, this is a shunted. and it may be just to make sure that until the process booted, the remote display is basically turned off decisively to give it a nice hard reset.

Perhaps because that's when it will be powered and because this has been glitching and this, the processor not booted in, this transistor has been turned on continually. It means that this has been acting as a current regulator. Instead of just small pulses, it's been running continuously regulating the short circuit current about 140 milliamps. which is a lot because the Uh it pulls the voltage down um, very Ripley voltage but the average would still be quite high and uh, 140 milliamps.

That translates to a lot of heat. Because this does operate in what's called its linear region, it operates like a resistor, right? Okay, next I'm going to do is I'm going to show the repair now I've already repaired a controller, but I'm going to turn the soldier iron on and I'm going to show the whole process again for the guys who want to be able to fix these themselves. So I'll turn the soldier on now on now and come back in a moment One moment please. The soldering iron is up to temperature.

Let's begin the repair. Here's what you'll need. You'll need the replacement capacitor 2200 microfarad, 25 volts. You will need some desilting breed or a desoldering suction pump optionally a pointy wooden cocktail stick.

These are useful for cleaning out the holes and double-sided boards and some lead-based solder. the flux core I do recommend lead based above lead free. Other things that will be useful would be this uh, flux pen which is basically a paint pen but when you pump it, it's got liquid flux inside and it just basically helps clean the contacts of the circuit board. That is optional though.

I'd like to thank a grant for sending this By the way, Um, two screwdrivers, right? The first one is a flat blade and we're going to use this to open this up. can I Just say that it says Dixel is the brand and that just makes me think of the Austin purse character. Dixie Dixie Enormous. Uh.

To get the cover off, you just pop it under here and there's two latches and at the other side you've got another couple of latches. Again, that just pushing the screwdriver up will release those. Now we have two screws. I'll just put that covers away.

We have a screw here with that cross head screw and we've got another one here between the live and neutral incoming. Supply Note that there's lots of holes for mountings, but they're not all used. Only two appear to be used, so we'll take that one out. Note the ones that the screw goes in because there aren't even pillars for some of the others.

and once the screws have been loosened, there's a little clip at the Each corner, so you do it at one side and then it should basically just lift up and then pull out and you can then tip it up and drop those screws out. Okay, now here are the soda connections. We're going to zoom down. This here are the two solder connections that we're going to do, the the ones where you can find out yourself as precaution.

At this point, it's really important to note the electrolytic capacitors are polarized. They have this stripe down one side marked with the negative symbols. It's really important you put it in the right way round. If you put it in the wrong way round, it will literally go bang.

It will pressurize and feel. uh, quite scary. So the gray stripes go away from the Transformer and to that end of the circuit board. So just think here's a Transformer there's capacitor.

The gray stripes go away from it. the negative so you want to hold that and I'd Recommend initially just touching a tiny bit of fresh solder onto these soda pads. So get your Soldier arm with a nice fresh, clean, shiny tip and uh, flow a little bit so drawn, then holding it at the back between a couple of fingers and supporting the circuit board. just apply very gentle downward pressure.

Do not force it, uh, just alternate between the sort of pads like this and each time you do it you can rock the capacitor very slightly, but don't drag it out. Don't use Force because if you do, it can damage the tracks. so you want to just keep alternating and rocking the capacitor very gently as you release those soda pads and at some point it will just pop right out it has just popped out. Then the flux or the suction pump is to basically the desoldering wick is to mop all the excess solder off that you want to mop it to the point that hopefully that hole will clear if the hole doesn't clear they've cleared in this instance.

But if they don't, take a wooden toothpick, heat the pad up and then just stuff the wooden, pick the toothpick down into the hole. And because the solder doesn't stick to the wood, when you take it back out, it will leave the hole clear. That's a useful tip in general for uh, repairing circuit boards. Is this bright enough? I Think it's bright enough.

Now get your new capacitor and observing the polarity. the long lead the positive is going towards the Transformer. The stripes are going away with the Transformer. Pop it into position and turn it over and hold it in.

or use something to hold it in. just whatever suits you. Ideally, it wouldn't be mounted hard against the circuit board. That would be quite useful.

Mounting off the circuit board a little bit, but it doesn't really matter. This gives it a little bit more rigidity for travel. Um, so now we're going to heat the pad and the lead and we're just going to bring up the temperature and then touch a bit of soldering onto solder onto the solder iron and that will then flow to actually make that solder joint. Checker Capacitor is roughly Street ish.

Don't force it if it isn't straight. Don't Force against the leads because that actually puts a lot of stress on the leads themselves and can damage the capacitor and then get the other one preheated with the solder iron quickly and then just basically a little bit more solder onto that one. The repair is done very straightforward. It's up to you if you want to leave the flux on or try and clean it off.

I Just leave it on. It doesn't really matter, it's standard electronic grid. flux does not cause corrosion. Don't use pipe joining flux because that does cause corrosion.

It wouldn't need cleaned after we use it in the first place. To be honest. Okay, now I'll just put this onto the tree and I'll plug it in and prove that it's working. So note that we've got the pillars here, but not at that side.

so this screw here is going to that pillar there. So we sit on at an angle underneath those clips at that side, and then gently use these ones back to let it just drop down into position. And I shall never get the cables. so this one is the neutral.

this one is the live. and I'll bring up the Hopi as a means of quick connection of these wires and I shall connect up. And what we should hear is that if it's working now, we should hear the relays clicking on and off. so power up.

There's a delay thing is booting up. the first really has come in and then after a while other relays will come in, probably to indicate there's a problem. there's the other relays clicked in and there. That's probably to indicate the fact that it's not got its temperature sensors so it's gone into some alarm mode and that is the repair complete.

and although that transistor had got hot I don't think it's been damaged, which is good. Um, but uh. I'll the person who sent this in our Center where we message about this about tests too. I would say that uh, basically speaking, get a good working one and measure the voltage between these two pins here, the ones that are going out to the keyboard and just make sure that it's somewhere.

Whatever voltage it is that the repaired unit is something similar, but it should basically be the open circuit on the smooth voltage. But that's it right? one moment, please. I'm just going to clear this off the bench. So the final bit of this repair is just as before: put it back, put that screw in the middle just to secure the circuit board down.

I Don't know if it's really actually needed because those clips do quite well at the side, but I'd recommend doing it anyway. Sometimes these connectors are quite tight. Good choice of connector. One interesting note about this design is that they the connections for the edge connectors.

They these plug connectors. They put multiple positions so they could move them backwards or forwards for fine tuning. I Thought that was quite a nice feature. and then after that, make sure that the label here where it says hotkey TTL is, uh, over to this connector here.

Just line them up, Check Everything looks alright. Press it down. This is where there's a real loud click Isn't there? Yeah, there's a Reload click and that's your controller. Hopefully fixed.

Um, so that's a good result. It just it shows how somebody just chipping out getting these capacitors, these gland capacitors. It's not a good economy to do that. It's always good to go with a prominent brand I'd choose something like perhaps Panasonic or something like that, and just to get a known lifespan out of something like this.

particularly in such an expensive product. Because those relays and these connectors and the Transformer they're all expensive products. Uh, the components and uh, to just basically hobble that with a cheap capacitor just seems a shame. But there we go.

that's it. fixed. Which is always a good result.