LFC#144 - MacBook Pro No Power, VRM Short

[Music] hello interwebs welcome to let's fix computers now with no camera flicker look you can see the reflection of my LED bench light very clearly and there's no flicker Thank You Logitech for updating the firmware for the Brio anyway this MacBook Pro doesn't turn on we've got a full battery full battery Oh huh when it was plugged in a moment ago our battery meter was saying full well that's just something we just learned anyway when I push the power button nothing happens so yeah we're gonna do a visual inspection there are some suspicious-looking marks that look like this thing is has something spilled on it of course the customer hasn't mentioned any of that but yes suspicious marks let's get this thing open and have a look at the inside hmm okay well this thing's actually fairly clean possibly something there see ya a slight shine on that plastic there that might be watermarks anyway let's start by disconnecting the battery because a bad battery can stop these things from turning on so we'll unplug that plug in a charger and let's see what it does right the green light on the charger press the power button no it's no nothing let's do a quick sanity check and see if the SFC is running I can't remember where PT bus g3 hop is on this thing so I'm just gonna wander around until I find it it'll be somewhere about that half of all all right there's PB 3 B 4 2 which is fine but I would expect that to be fine because we have a green light again that big cap I'm expecting that to be either pp bus g3 hot or just charge a voltage and that's sitting up 0.8 volts nothing runs at 0.8 volts so that seems very odd so there's something going on with this fellow I think we're gonna have to take the board out have a look at the other side and find out what's going on with this thing okay so we're gonna get this board out of the laptop now I haven't looked up exactly the locations for where PQ bus g3 hop is yet but the thing is we know just from this from the quick measurements I took that there is a problem with it and that is almost certainly gonna require me to remove the board to find so we'll just get on with it [Music] well back of the board is fairly clean all things considered there's dust here and stuff like that but I've seen much worse but a little green spot between those two big dudes there and if that's something could be interesting maybe a bit of corrosion is leaking current off of a high current line maybe I don't know I'm opposed to look at all of this in a sec we'll take we'll take those speaker bit off in that kind of thing and we'll have a closer look at those voltage rails and find out exactly where that missing voltage is or find out where we're dropping it first because I want to see if that's coming in at the charger or whether it's being lost somewhere in peak of us 2 3 ha [Music] okay right so let's quickly pull off the speaker for this just so we can have a closer look under there make sure there's nothing horrifying which again that doesn't seem to be really clean board apart from the usual sort of general dust and stuff this up in this area right there's our 18.5 from the charger now I think this guy down here I think that's the main coil for run pp bus g3 heart so I'm gonna have a quick look at that yeah I think that is and once again we've got that point well point nine volts so let's just double-check that that is what I think it is so we'll quickly switch over to the board view and we look at else 7030 down here yeah keep the bad g3 hot charge of regulator well yeah that's close enough there's Pete bustin three hot and okay there we go there's a diode up there there's the actual PT bus cheery heart and also a resistor over there so let's just grab that guy and just verify that yeah so people verse three three height is low so I think what we need to do now is we need to disconnect the output of pp bus g3 hot and see if the rail comes up again because that will tell us whether B fault is in the source of PP butter two three hot or somewhere else in the system and that obviously will drastically narrow things down so let's switch over to a schematic and look up the source of pinky between three car all right so here's our 2936 schematic and when we go TP bus underscore gene 3h goal and we're looking for that as an output outlook there we go right so f 70/40 there's the fuse for PB bus g3 ha let's find that going F 1740 all right where are you you're on the top of the board okay that's near to where I was originally measuring so let's flip the board over and we want to disconnect that fuse all right so we just can do a little bit of preheating from a distance I'm holding the hot-air gun a bit cack-handed just so we're not blowing directly onto and all of the RAM and stuff like that actually I could just rotate the board around for that don't forget to rotate the the computer instead of holding your tools cack-handed cool all right well let that guy cool off again and then we'll measure PG bust g3 hot and we'll see what has changed so we should find a PP but PP bust g3 hot comes up to its full fat 12 volts now at this point if it doesn't then that tells us that there's a problem with the power rail rather than somewhere in the system I've just realized at this point I've forgotten to clean up the board first so that's a bit embarrassing I sure hope it wasn't that simple although to be honest I don't think there's anything there that could be it I don't see anything on there that looks like it could be causing a problem not even that little scummy bit that I pointed out there we go twelve point six so that is a running SMC so that's the other good news is it's not the SMC which is good because that's game over for me well good if I'm gonna replace an SMC so so our output from PT bus g3 hot is good which means there is a fault somewhere else in the system so something in the system has shorted out and is dragging PP bus g3 got to ground okay right so we have a dead short on PT bus two three hot so with the with the fuse removed if I go from I'll go from ground to the other side of the fuse there as you can see we have no resistance at all so something has gone pop hardcore but there's no signs of issues on the board completely invisible whatever it is so I'm going to inject voltage and we're gonna see if that will show this up so I've got a couple of fairly heavy wires here and we're going to solder them on to pp bus g3 hot so we can directly interface at the board so now we're going to start pumping power into this and we're gonna see where it warms up okay and we're gonna start so one volt and a half an amp here we go and let's just squirt a little bit of alcohol on it and see what dries out not on that side unlikely cuz there's not a lot of people gushy to be hot on that side of the board anyway how about over here I've been doing over there okay let's give it a bit more juice okay that's a noun no nothing doing there [Music] I think we're gonna need to give it a bit more all right it's one and a half no no still nothing going on on that side just take the cap off of the PCH just so we can expose a bit more of the board now no heat on either of those guys either okay to answer it is where is that power going someone on this board is eating three watts now someone's sitting there taking three watts of power like a champ [Music] found it [Music] on the other side of the board next to the fan you something down there I think it's that cat there oh and that one okay let's investigate that area I think we might be getting somewhere hard to tell then these guys were warming up however as soon as I put my finger on them my feet my finger just he soaked all of that heat back off of the board again so it's kind of hard to tell what are they first of all right those guys TV the P P thus s Phi that HS computing right are those guys shortage ground then guessing so so that's these guys here so let's just put a measure on those ground and also ground so these guys could have been doing it now big devices so if they're both shorted they could be soaking up a lot let's take them off the board and see what happens [Music] right has the short gun interesting all right what about the caps themselves [Music] yeah that's dad goes fine that guy doesn't look fine all right well we've got one dead cap which does have a burn mark on it as well so what's the let's see what I drop across and see what I drop across PCBUs g3 hot is [Music] okay I'm sure across PP bust g3 heart is gone so stick the working one back on the board we can probably do a test with only one of those cats so that's the one that's not bad [Music] okay let's check that are short hasn't appeared again I hate it when that happens BB no beeps and the resistance is a lot good Oh Kai right so let's get the fuse back on and see if it's to us so I need my sword ring again oh no I saw it I saw it no we're fostering that as well don't ask me why I'm trying to be a soldering iron hero I guess I just don't like being reliant on the hot air it makes things so easy but it's very easy to be dependent on it splice back on let's blow this bad boy up all right our survey says AE as a spinning fan I'm going to turn it off again straight away because there's no heat sinks on it oh okay right get x on so what is this capacitor what does it do and what is it supposed to be we have left off C 75 60 or C 75 30 we took off both of them and I think I think it was this one that was gone but I moved I moved this one over to there because they're in parallel so doesn't matter which one goes where let's get this go Matic up on screen and find out what that actually is so 29:36 holy crap that was good that was that CPU vehicle there's 7 560 over there on the auxilary face or 775 40 there it is yeah the auxilary face must be the other one that was over on the left phew okay so what are the rating on those caps what are they supposed to be 33 mic 16 volt tantalum alright so the bad news is I don't have one of those they're marked as critical so I can't leave it off the board I think I wonder if I can rob one from somewhere I wonder if I can Nick one from my old practice board I don't really want to kill this board though hmm let's see if we can sacrifice the practice board to make some money on this one right so the practice board is at 25 to 30 so let's open the 2530 board view and check if it's got any 33 Mike's 16 volt and the lung capacitors on it it probably has there's one what's this battery charger oh that's awesome I don't need the battery charger to work on this oh wait oh there's Beauty busty three hot I kind of want that to work although we could come back and try and fix that a later day I'm taking it see 7000 day I'm stealing you see 7000 date okay it's the big one up near the battery connector just a bad boy there right you gettin robbed [Music] there we go lovely pair of capacitors check our work again and now we've got lots of kilo ohms and it's charging up beautiful okay right let's get all the bits reattached to this board so we can start it up so this little heatsink those are just thermal pads those can go straight back on and we'll get some new thermal paste onto the CPU just to make sure that that guy is happy [Music] you [Music] [Music] alright time to find out if it was all in vain its chimed the screen has lit up Apple loading screen SSD boot time BAM I'm happy I'm very happy all right so we're all done so we had a short circuit across one of the tantalum filter caps on the CPU and power supply it wasn't on CPU decoupling itself it was on one of the vehicle phases so yeah lucky escape I'm amazed that it hadn't blown something up cool right thank you very much for watching everyone I'll see you all next time good bye come out [Music]

Channel: Adamant IT

Views: 68,495

Keywords: adamant it, adamantit, computer, repair, shop, custom, gaming, modding, apple, macbook, pro, fix, green, light

Id: 871jg1w2ZY8

Length: 22min 20sec (1340 seconds)

Published: Thu Aug 09 2018