A digital laser tachometer that isn't working and this one came with a note that says here's a digital Tachometer I Mentioned on Patreon. This device worked fine the first time I used it three months later, pulled it out to use again. The battery was flat, added a new one and it worked fine, but about 10 minutes later I picked it up and it would not power on. Check the battery again.

it was extremely hot as I've shorted now fails to power on its own. Check the reviews which are surprisingly positive. There are a large number of one star reviews mentioning Bash issues and device feeling within A few uses. Excellent.

That's interesting. So the first thing I suspect when I see something like this, but let's hook some clips onto it. Let's get nine volts into Current Limited. So I'm setting this is designed for a Noble Bash I'm setting this for about 9 volts.

The current limit on the power supply is set to 500 milliamps. so I'll connect this to negative and this to positive. instantly seeing a spark. It's drawing the full current and it's the voltage drop to 0.17 This thing has an internal fault.

The fact it works in the first place doesn't look like a simple polarity spot. Let's open it up. so four screws I don't know how the front's on. It looks like a separate piece of cover on here.

I Don't know if it pops off the front to allow the case to open or if taking these screws out will be enough. That'd be hand if it was. It just opens up like this. right here.

There's a laser. Joe's interesting. Just the first thing I'm seeing is the laser has multiple positions it could be mounted in I Guess it? that's just to tune it to the lens in the front of the unit and there's the little uh sensor for receiving the signal back. But I'll tell you what.

I'm going to get a thermal imaging camera into this first of all because I just know that it's most likely to be something like a capacitor. Now let's see. uh. negative is actually black.

Well that's nice. Not like a recent product. I got where negative turned out not to be black. or actually it did turn out to be black but just connect to the wrong thing.

Look at the Sparks coming off this so something will be getting hot. I will actually turn the current up a bit just so it gets super visible hot. Let me grab my thermal imaging camera. I'm going to use my new infrared one for this because it's very impressive.

It's one of the higher resolution units I Could use the uh other one for this but it's this one's got the extra lens built onto it. it just Clips in the front magnetically this uh plugs into your USB port I saw this in Max electric stuff I thought it looks pretty good and you know what? it is pretty good for the cost. it's amazing. So I shall uh unlock my phone? I'm going to use this thing that has on the Go enabled.

Uh, where is the P2 Pro Plug the device in and turn on the OTG function. I shall plug it in here and it Powers up. We actually left the thing off until it was ready and I'm immediately seeing two things that are hot. what's hottest.

I'm seeing a reflection for a start. over there. you have to care for that, but this thing here is hot. Let's Get Closer I've got the lens on, so I should be able to get fairly close to this.

You see that that looks suspiciously like capacitor. Let me just, uh, work out where that is. It's there. It's this capacitor here.

Okay, did you see that? All right? Did you see how? Yeah, That's uh. let me bring it over into position here so you can see see the whole component there. Okay, thermal imaging cameras. very useful for spotting bad capacitors.

The other thing you can use is a simple thermocouple probe just touching it to each capacitor and turn. That's a much cheaper approach. You've maybe even got a thermocouple probe already. so I'm just going to take a look at that.

The first thing that comes to mind is actually just turn the power off. Get the soldier iron on. I'm just desoldering that capacitor. Is there anything visible? The capacitor doesn't look nice and it's got flux all around it suggesting it has been.

Uh, there it is there. It just doesn't look nice that that one there looks good. That one there does not look so good. Uh, we'll remove it.

That's the best bet. Best way to remove these. A couple of approaches. you can do that laziest if you can get around.

it is just to cut it out. That can damage tracks though. So I've got the Soldier Iron on I'm just going to let the soldier and heat up one moment, please. The soldier line is up to temperature, so my way of taking these capacitors out these little fiddly surface mount ones is to apply a little bit of solder to either side just to wet the joints, but apply an excess so it wells off a bit above the capacitor and then place the silver iron on top and try and heat both connections at once until it just basically slides off.

it has slid off. No. I'm going to connect that to my volts again and see if that has cleared the fault. If it is a simple decoupling capacitor, it may not be that critical to the operation of the unit.

Depends what its function is. Bench power supply. Onto the negative and the positive not seeing Sparks this time. Uh Current is.

well, the power supply is off. That'll be why we're spy. Now on current showing a zero test. Do you have to press it? Yeah.

See, that's it. operating. Now that capacitor appears to be current is 37 milliamps rightio? Let's test this. Uh, I'll put it back together.

We'll put a batch in it and just see if it operates like that without that capacitor One moment, please. So to test this: I've stuck a small piece of double-sided uh reflective tape onto the shaft of this open chassis shaver. I Just got this to tick apart. so I thought it was quite interesting.

It is now spinning I shall hold the test button, point it at it, assume this is how you're supposed to use it and it's held the reading of 5481 RPM which sounds reasonable enough for that, sort of. for that sort of speed. Release it. it resets to zero point at it again.

5514 RPM and again I Think it will just grab the faster speed 5529 so that looks to all intents and properties as if it's working. Okay, this is a USBC rechargeable. It's quite nice just because of the way. everything.

it's really skeletal. It's got the motor sticking out the end and then shaking. the sort of the vibratory blade mechanism. But let me show you why these capacitors are failing so much.

because they have become a blight of the modern electronic industry. Let me just grab my notepad here. Oh, let me just uh. dig deep for grabbing.

Notepad The construction of an Ml CC multi-layer ceramic pasture is like this: You have alternate layers of ceramic and in that alternating between the layers of ceramic material are thin layers of metal with uh, have them connected to one side and half of them connected to other. There are other constructions for more sophisticated capacitors, but from the other side we've got interleaving capacitors. This is all shown in a very simplified manner under what that results in. Because they go super super thin layers, it means that they can fit a huge capacitance in a very small area.

It's like that tiny little block there can have like a value of like 10 microfarad because that's equivalent to a really large area. It's because there are such thin layers. The downside that is the tiniest little fracture in that causes those plates to just shift slightly and then you end up the dead short circuit between them. This is so common it is making so much stuff feel.

Fortunately, they go very hot and they do it. although sometimes I've found in some pattern, thread detectors and things up. they just cause a slight, they just take a resistance on and it means that you've got a battery operated product and you think it's not lasting very long. The batteries and the answer is that uh, the capacitor has just developed that resistance and it's just discharging the battery over time.

But interesting enough device. It's very simple inside. it is basically just the laser shining out looking for that reflection back to get picked up with a photo sensor and then it's just evening out that it's disregarding backgrounds of Illumination noise and it's just getting a value based on the Pulses from the rotation. so that is it fixed.

Uh, ideally you would change that capacitor for a new one that is of the same value. But here is the downside. Those capacitors don't have values marked on them. so unless you've got a working unit that you can measure the capacitance in and that really involves taking it out of the circuit, then it's very hard to find an exact match.

What usually happens with things like, well, Apple products is a good example. They seem to to suffer from that quite a bit. You'll get donor boards that are completely destroyed and they'll take that capacitor from that same position and they'll solder into that, but on the basis that it's around the power supply area I'd Guess probably a 100 nanofarad would do that, but that is it. The curse of Mlcc capacitors.