Transcription
Hello SCB, back! And this time, we have a nice laptop to repair. You remember those laptops? I mean, yeah, this is old, probably over 10 years, but anything that is faulty on this laptop can be repaired. So, this job is coming from a local repair shop, $80, decent money. So, we have a Satellite C A5 Z. Okay, the problem with this one? Not charging. I mean, every customer, yeah, when the laptop is dying, the customer will say, "Not charging." The customer will never say, you know, "My laptop is dead, it's not doing anything." No, it's not charging. So, pressing the power button, nothing happened. Let's plug the charger. Plug in the charger, check on the screen. It's taking no current at all. Nothing. Pressing the power button, nothing. You can see, so this laptop is dead. It's not like it's not charging, it's not coming on also.
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I will say, let's open the laptop and try to have a look inside. I'm pretty sure we can repair this. We have like a normal hard drive inside, we have the BIOS battery there, RAM memory, detachable battery. That's how the laptops used to be in the past. Now, speaking about common faults, what is the common fault with this one? You remember the charging port? The middle wire always gets, uh, broken on this, uh, model. But maybe we are wrong, maybe something else. But looks like the power is not going inside of the laptop. I think we have screws from the keyboard side. Yeah. Huh. Detachable keyboard. Yeah. And the laptop, it's open. Check here. CPU on the socket. You see? You see? And the charging port. No, no, it's not a charging port. Okay, fantastic.
Let's plug the charger and let's diagnose this laptop. So, plug in the charger. Good. Let's check the voltage first. Let's check the input voltage of the charging connector. And we have 19.8. Check on the screen. Yeah, 19.8 volts. The main power rail. Main power rail, very simple to be found. You see capacitors, capacitors, capacitors. So, checking the main power rail and we have 0.9 volts. H, which is not right. 0.9 volts. Why is that? Why we have 0.9? Well, let's come, yeah, with the power supply. Let's lower the voltage. Yeah, like 0.9 volts. So, we need a ground. HDMI port is a good ground. Let's see. The ground is good. Good. Perfect. Four arms. L, maybe it's too much. But let's see. So, we have the capacitors and it's not short. Huh? It's not short. The main is not shorted. Yeah, you're right. We seen there like 0.9 volts, so it cannot be shorted.
Well, on this case, we have to diagnose and repair the, uh, power input circuit, which is probably on the other side of the board. So, we have to take the board out and try to have a look there because we don't have voltage on the main power rail. Dodgy repair? Anyone said dodgy repair? Dodgy repair is like, I will show you how it's like. It's like 19 volts here. Plug in the charger and obviously the laptop is not working. Let me plug the power button, which is this one. To plug in the power button. Let's press the power button. Nothing happened. Obviously, because we have 0.9 volts on the main power rail. But coming with the, with a power supply with 19 volts here, pressing the power button and the laptop is coming on. Huh? How? Well, we just supply power where it's missing. Enter password. L, this laptop has a BIOS password. We supply power where it's missing. You remember I told you here has to be the main power rail, which is 19 volts. So, we know the laptop is good and we know the problem is on, uh, the main power rail. Can you use a wire from here to here? Yeah, of course. But again, that's too dodgy. Let's take the motherboard out.
So, what could be the problem? The problem can be the BQ chip, which is the power management chip. But I believe, what do we have here? Before checking, yeah, I believe probably the second MOSFET is shorted. That's what I believe. Well, let's see. We have a cable here and that's all. The motherboard, it's out. Now, let's have a look at the other side of the motherboard on the input circuit. So, check here. Yeah, the plus of the charge input. You can see here, two pins. Plus is coming to an inductor, from the inductor is going to the fuse, and from the fuse, yeah, it's coming straight here. So, you have the first MOSFET, then you have the second MOSFET here, and at the output of the second MOSFET, you have a current resistor. Those two tracks are going to the BQ chip and are used to read the current across the resistor. And from here, you have the main power rail. So, plug in the charger. Let me grab the charging port. Okay, so I connect the charging port to the motherboard. So, we have power. Yeah. So, checking like I said, here is the plus, right? We have 19.8. Here, we have 19.8. After the fuse, we have 19.8. At the input of this MOSFET, we have 19.8. At the output of this MOSFET, we have 0.9. So, you see, this is the point where actually the power is disappearing. I mean, it's meant to pass the MOSFET, the first MOSFET, but it's not doing it. Why is not doing it? Because on the gate, we have 0.9, and of course, on the output, we have 0.9. Now, what is the reason? Let's check the second MOSFET. Yeah, let's check. So, the first MOSFET clearly is not burnt. But the second MOSFET, check on the screen. Check on the screen. 2 ohms. So, the second MOSFET is shorted. And the BQ chip has a, has a circuit which it will detect if you have like a short at the MOSFET, and on that moment, it will cut the power on the first MOSFET. So, now you understand the issue. Yeah, shorted MOSFET. Let's remove the MOSFET. This is a channel and MOSFET. So, the MOSFET is removed. Good. Now, let's show to find another MOSFET. So, how we are finding MOSFETs? If you have spare boards, usually the, the switching power supply, they have channel and MOSFETs. So, we just, you know, we are taking one MOSFET from here and move it on our board. Now, have in mind, the MOSFETs, uh, from the input circuit are not switching. So, basically, you can use any MOSFET here. Okay, let's solder this MOSFET here. Perfect. So, the MOSFET is, so the on place. Now, the question is, the motherboard is working? Is repaired? We can buy some pizza? That's the question now. Let me cool down a little bit this area. Good. Now, we can plug the charger. So, plug in the charger and it's taking no current. Interesting. Let's check the main power rail. So, the main power rail is 19.8. Check on the screen. It is 19.8. It is. So, basically, if we are pressing the power button, let's press the power button, which was here, right here or here? Where was the power button? Here was the power button. So, if we are pressing the power button, check on the screen, like 700 milliamps. The LEDs are on and the board, it's on. Okay, working fine. Okay, what about charging? Sorry. Yeah, let's see. Unplugging the charger. Let's plug the battery. So, the battery, we have plus and minus, right? Plus. So, this is plus. Not sure if it's coming like that, but let's check. Let's see which is ground on our connector. Ground is here. So, that's mean the battery has to be like that. Good. The battery is connected. Plug in the charger. Check that 1.7 amps and we have the orange light here, you can see it. So, it's charging fine. Pretty cool. Yeah, the laptop is ready. Can we power on? Yeah, of course. We can power on the laptop and you can see the current is going up. We have the power on light here. Fan is not spinning because the CPU is not hot. Okay.
So, few tips and tricks about the power input circuit. Let's go under the microscope and have a look again. So, on a power input circuit like this, we have channel and MOSFETs. Obviously, on the input, you have 19.8. On the output, you have 19.8. Then it's going to the second MOSFET, and on the second MOSFET output, 19.8. On the gate, yeah, on the gate, we have 25 volts, right? Should be 25. Let's see. Here we have 25.3. Here, and also we should have 25.3 here. You can see on the screen. We do have 25.3, which is actually 6 volts. So, if I check actually the gate with the source, we have 5.5 volts, which is fine. And here, we have gate to source 5.5 volts, which is normal. Okay, good. Let me put all back together. Yeah, just give me like five minutes. Okay, so everything is back in place. Check here, charging LED, and it's taking 1.2 amps. Pressing the power button and the laptop, it is coming going. You can see it. And it's asking for password, which is not our problem. Yeah, the laptop came like, uh, no power. BIOS password, that's a different story for another video. But the job is done. Yeah, so we fixed was a dead laptop, came with no power, not charging, actually, and we fixed it. Now, just to understand, yeah, because those MOSFETs, they are not switching. You know, switching MOSFET coming on, off, on, off, you know, the chance to get burnt is not that high compared with the MOSFETs from the input circuit, which they constantly carry current. Yeah, like the charging current, the current which need for the laptop in order to work. That's the reason why many times you find those MOSFETs from the input circuit burnt. Now, let's say we have this amount of laptops which they have faults which can be repaired. Now, over 50% from those laptops, yeah, which can be repaired, the problem is from the input circuits. And just checking like simple things like I showed you, you check the main power rail, see if it's short. You can come with a power supply, try to, you know, trigger a power on, or checking the first to MOSFETs, see if they are shorted or not, checking the gate BT AG. You've seen that you will fix over 50% from the laptops which actually can be repaired because most of the faults they are on the input circuit. Remember, especially on the gaming laptops. On the gaming laptops, you have the first MOSFET which is getting shorted. On this one, it was the second one. I'm just saying because, you know, when you think, okay, motherboard, PS, and motherboard, they are some complex things, you know, it's, it's, you need a lot of ton or of experience in order to fix motherboards. Whatever is there. But like how I said, and I will repeat one more time, over 50% are on the input circuit because that MOSFETs are always under high current. If everything is there, probably I'll move to the BQ chip, which actually is the driver of those MOSFETs. Usually, I found like the, the 25 volts is missing, and that's 25 volt is coming from the BQ chip. Anyway, I'm going to stop now. I will say thank you for watching. You know, just like, subscribe if you like the video, and, uh, see you on the next one. Bye.