Asus TP300L Laptop No power Repair - Testing for Faulty Mosfets.

here we have an asus laptop that came in for no power i do not know the model number on this asus laptop but i'll leave it in the title i need to look at the back cover and i do not have the back cover next to me but it looks something like this touch and the inside looks something like this the laptop is dead absolutely no signs of power let's plug the charging cable just to confirm okay the charging cable is plugged in and if we press on the power button right here nothing dead while the laptop is plugged in let's quickly inspect it under a thermal cam just to see if there's anything obvious okay and nothing obvious at all no heat spots anywhere on the board while the charge is still plugged in let's do some measurements i want to look for the two power mosfets and i see two of them right here and let's measure what do we get if we measure here we get 19 volts 19 volts if we measure here and 19 volts is not passing through we have zero volts what about our gate we have zero volts on our gate and of course we're gonna have zero here and we do not care after this point here right now we have 19 volts here and the other thing i want to check is if we have a shorter ground meter in diode mode actually i need to unplug first otherwise we're going to get this short to ground so let's measure and we don't have a shorter ground we have a voltage drop of 0.49 which is perfect right now the problem is 19 volts is going in but it's not coming out since we do not have a short on the drain of the second mosfet here we know that we do not have a short circuit on the board so we want to test the condition of the mosfets and see if they are good metering contributing mode and let's test from drain to source we should not have a continuous path otherwise 19 volts would have passed and if we test from drain to gate no short and if we test from source to gate and look at that we have a short between source to gate and that's not good that's a very good indication that our mosfet is bad what if we test here drain to source nothing drain to gate and gate to source we have a short here too right now we do not know if the problem is this mosfet this mosfet or both of them we're going to start by removing this mosfet here and then we're going to test for a short between source and gate on this mosfet if we no longer have a short here then we know that the problem is this one here if we do remove this and we still have a short here then we're going to remove this mosfet and test for short again and see what happens of elimination so let's start with mosfet number one is an n channel mosfet 30 volts and let's measure metering continuity mode and we're going to measure between here and here and we still have a short so it could be that this mosfet is what's bad let's remove this one and now we're going to measure to see if we still have a short between sourcing gate do we have a short from here to here and look at that we no longer have a short we no longer have a short between gate and source what about here we no longer have a short between gate and source so this mosfet was probably good or it's possible that that mosfet is also bad but one way to find out right now you see a blob here and a block here but that doesn't matter because all those three pins are connected and all those four pins are connected let me get rid of the glare much better so let's see what happens if we solder that back let's see are we going to get a short between sourcing gate meter in continuity mode and we're going to measure from here to here and we do not have a short so this mosfet is good now we have to replace this mosfet and where do we find it from right now i have a donor board right next to me and this is a very common mosfet used on most laptops so we're gonna try to extract it from a donor board i have next to me we should have that mosfet in stock but i do not want to look for it right now i have a donor board here that we can extract it from this is an n channel 30 volt mosfet on asus laptops usually it's an e4 or e5 and this one should be like this and let's prep those pads here right now before we plug the charging cable i'm gonna connect the screen cable again i had to disconnect it so that when we solder the mosfets here we're not gonna end up burning that cable all right and let's see plug the cable in and maybe we can plug the battery in as well and look at that we see a light here tada windows is loading as you can see and the job is done let me know what you think i hope you enjoyed this video don't forget to like and subscribe leave a comment if you have any questions and we'll do something else in the next video [Music] you

Channel: NorthridgeFix

Views: 24,103

Rating: 4.9624338 out of 5

Keywords: asus tp300l laptop repair, asus laptop repair, laptop repair, no power repair, testing faulty mosfets, test mosfets, laptop mosfets, asus laptop no power repair

Id: DFIcDCNIRhk

Length: 8min 11sec (491 seconds)

Published: Mon Oct 04 2021