Hi just another quick video on the USB power supply now I know this is completely out of order I haven't done the uh schematic I haven't been through the schematic and the design decisions and everything for this yet. Don't worry I will get on to it. so I know it's completely out of order but I was just uh, troubleshooting this thing or well, I was about to it needs some uh, troubleshooting cuz I've hit a bit of a snag with the uh DC to DC converted down in here. you um, seen a previous video of me soldering uh that thing and it's a bit of a drama now.

I've gotten to a point where of course you know I thought oh yeah I solded everything together I thought it all work. so I did some firmware and of course I got a hello World going here it is Tada hello world So it all works so the firmware Works beautifully. but the DC todc converter in there doesn't seem to be switching on and uh well I thought I'd troubleshoot it. might as well switch on the camera camera.

Let's go now. of course the first thing I suspected here was this pain in the ass little5 mm pitch uh, leadless chip which we've looked at soering before. They're a real pain in the ass. so I thoroughly inspected that I even took it off and replaced it and well, no, it it exactly the same issue now.

I'll show you what's actually happening I've got ground down here and let's uh, probe the input if you have a look at the circuit there, this is the input to the DC DC converter on this inductor. Here, you'll notice that it's 5.14 volts. Okay, so that's across C24 there. that's the input side to the inductor pins 10 and 11 of the chip there.

And of course, you can't really get down and probe the exact pin on the chip. It's not like you know an S so1 where you can't actually uh, probe the uh pin down there. So um, you know you've just got to uh, inspect it and rely on the fact that you know you've inspected the joint and uh, and it's all good. But we can do some resistance measurements.

So let's switch the meter over here and let's uh. First of all, well, actually no, sorry I didn't finish showing you what the problem was Here we go. So the problem is, we've got 5.14 volts on the inputs here and we've got on the output 5.1 142 exactly the same voltage on the input and output of the inductor there, which shows that um, the switch pins seven and eight there of the IC are not switching to ground and this uh, DC to DC converter is not switched on I don't even need my oscilloscope there to probe that switching point to see if it's switching or not I know it's not switching. it's the exact same DC voltage.

So clearly that DC to DC converter is not turned on. Why? and well, um, what? I uh suspect is that it may have been something to do with Q Uh two around there and I've been I've actually played around with the software in here I've been playing around for a little while and uh, so what I decided to do is short out Q2 and that's exactly what I did just take that out of the equation and I replaced R2 under there. sorry R Yes, R2 Um, it's supposed to be 12K but I actually replaced it with Uh 50 1K just to eliminate that uh Q2 control aspect from the DC to DC converter. So it should.

As soon as you power it up and apply 5 volts to the input, it should give you, you know, a much higher output voltage. It should boost it up, but it's not the output voltage. and uh, of course we can see the drop on the dide here as well. Okay, here's the input voltage: 5143 5143 and then the output side of the diode here is 4.98 So because the rest of the circuit is going to draw some uh, you know, some current.

So uh, we've got a voltage drop across our diode there. It all looks quite reasonable. So going to actually do some resistance measurements here, let's switch it over. and of course, the output's not going to be shorted.

The output of the diode there. the power rail. uh VR there. That one's not going to be shorted at all and you can measure it.

it's jumping around. You know we can Auto Range that to sort of. um, you know, give us like a ballpark of what going on there, but it's definitely not shorted. Okay, so it was confusing.

The auto Ranger there mucking around. it does that sometimes on various meters. Um, this fluke is no exception. Now Uh, let's measure the feedback point which is pin if I look at the schematic pin three which is um, the R6 in there.

where is it down down there? that will be the Fe feedback pin and there you go. Once again, it's jumping. Oh there there we go. The feedback pin is roughly 10K and you'll notice that R6 there is 10K to ground so it's just under that.

So there's impedance there. You know impedance in parallel across that due to the feedback pin of the chip, everything's just fine. And if we measure the VR rail which is the output voltage which is here with that point, let's so let's probe that and what do we get H it's it's a bit low. It's supposed to be 51k, but uh, that could be the input resistance of the uh, the input impedance of the chip.

Let's swap the leads around so it could be something loading that down. No, that's there. we go. Yeah, it's climbing.

I Mean, it's supposed to be 51k, but you know it's got all sorts of stuff in parallel with it. So really, um, uh, that like there's nothing shorted, there doesn't seem to be anything open, seems to be working just fine, but this stupid thing does not start up now. I've actually looked at this uh, under the microscope multiple times and it, uh, definitely. I mean it might look a bit messy.

there's lots of flux residue there. I've been mucking around with the soldering on this thing, but it it. Trust me, it actually looks quite good. So it's face palm time folks.

Can you see the problem? I can say I just found it I've been looking at this for quite some time I've double checked things to make sure the components were in the right place and well I have overlooked it. Check it out. look for C26, which is the capacitor which is the uh bypass capacitor on the upper resistor R2 there. where's C26 down here? C26? What fail I've blood idiot I've put a 10K resistor in there 103 There It Is That is supposed to be 100 puff uh bypass cap for the upper part of the voltage divider for this DC to DC converter.

so I put a 10K resistor in there. What an idiot. So that's actually if you follow the trace in because it goes that goes through to here and then that point there goes up under the up, through under the diode there around to here through this resistor. so it's in parallel with that 51k.

it's in parallel with that. uh, what is it R2 There it's in parallel with R2 so that's it's supposed to be 51k but it's 10K in parallel with 51k. No wonder this bloody thing is not starting up. Unbelievable man.

I've looked at this multiple times. would you believe it? and I did not see that. couldn't see the forest for the trees. That's what happens when you try and check your own stuff.

Murphy will get you every time. What a pain in the ass man. I've been think I've been changing this chip and I inspecting it and scratching my head and doing all sorts of stuff. and there it is.

a simple, stupid component in the wrong place. solder in Iron time. Well, that was pretty darn embarrassing man. I Thought it' be something more obscurer than just a stupid idiotic mistake like that.

but duee to Murphy's I absolutely missed it actually. I won't power that up yet. Let's uh, measure the resistance of this. uh Point Again, you know how we're getting what 8 10K or something 8K before? Basically we're measuring.

um R2 There There we go. No, it's it's all over the shop. it's jumping around. It's confusing.

The auto Ranger there. Let's uh. take that, that's 600k. Let's put it there.

That'll do there. We go. 30 charging up. Boom.

No problem whatsoever and that should eventually. Well, there we go. It's going to settle on about 40, but It's yeah, we'll getting you know 8 or 10K before which was kind of a a dead giveaway really with uh hin site. but um, you know it could have been the feedback pin on that uh chip there causing or you know, other stuff causing an issue.

um to measure R2 in circuit like that and uh, well you know. But there you go. Um, so we've replaced that, it should be good. So let's power this thing up.

That should start. I Think we're expecting about 7.6 volts out or something. Uh, because it will be uh 51k. Um, it's the upper resistor divided by the lower resistance.

So 51k on 10K + 1 times. Uh, the reference voltage of the DC to DC converter 1.24 5 Vols Um, let's see what we get here. 5.1 volts in and what fail? Still fail 5.11 volts out. It chip is still not going son of a well.

I Just went and inspected and reflowed that chip again. I'm absolutely sure it. uh, you know there's nothing else wrong now. Yeah, I was absolutely sure before too when the stupid resistor was in the wrong place.

But anyway. uh, let's give it a go. Output voltage: hey Bingo 8.14 volts H Oh actually that's yeah, that's higher than the predicted value because um, the transistor is still uh, in place, shorted out. There's R26 down there which goes off to the rest of the circuit.

if we actually lifted R26 there, uh, got rid of the rest of the Uh circuit, we would find that it would be on spot on to the predicted value. Hey, why not try that? Got the solder n all right. I've removed r26 there and we should get reasonably close to our predicted 7.6 Vols should be a bit of Tolerance there. that's our output.

There we go. 7.72 3 Near enough. I'm using like 5% resistors or something horrible in there at the moment. Uh, for that 51k so that looks like, uh, it is working.

An absolute treat. So there you go. That's two uh things. There is the uh bias.

You know, the personal bias when you're inspecting your own circuits. I Simply did not see that resistor in there. that, uh, that one down in there. It just did not see it if we attempt to have a look at the joints of that chip under the Mantis microscope here.

they look quite decent. good enough, and uh, but they looked like that before I reflowed the things as well. so you know. Obviously it didn't take on the chips somehow, so just something to watch out for.

Real pain in the butt when in doubt. Reflow So there you go. That was a pretty easy trivial fix in the end. and uh, a classic mistake there.

There were two uh, mistakes. The first one was I simply had the wrong component in there I stuffed a resistor in there instead of a capacitor. My brain was elsewhere when I was populating this thing. Eh, it happens all the time.

and of course it was right next to a capacitor which I you know I didn't really look at the circuit thoroughly and actually go through it step by step and check and well I've said it before and I'll say it again. Do not assume anything in electronics I thought that mate, you know that capacitor I think I know know what my mindset was there. Oh, this capacitor was the one that was the bypass capacitor in the circuit and no I didn't look at the designators there and I had the wrong one. Absolute classic and of course the other one was soldering this pain in the ass.

5 mm leadless uh chip real mungro I just had to Reflow uh, the joints in there before I actually got the thing working but hey, it's working now I I Don't trust this package any further than I can throw it if I'm getting issues hand soldering these things I don't know what's going to happen in production, not getting a good vibe I may end up changing that sucker I Don't know. but anyway, for now it works and uh, there you go. That's a little troubleshooting of the Uh USB power supply. There'll be a lot more videos to come, trust me.

I Just want to get this thing up and running first actually doing what I want before I go through the whole design aspect of it I Know it's a bit back to front but stick with me. We'll get there eventually. Hope you enjoyed it. Catch you next time.