Thanks for the interesting video Richard. While watching I noticed two things that might save you some trouble down the line. First, at 20:28 there is some dark spot on the traces below the northbridge. This may just be dirt but might also be 2 or 3 burnt traces. Second when you applied leaded solder to the MOSFETS to aid removal at 52:57 you spilled a solder blob between pins 18 and 19 of the Richtek chip and two adjacent resistors.
Thanks for the video. I didn't think I'd see double low side mosfets shorted, never mind on two phases. Also, thanks for pointing out that the controller may cause a short to ground as well through the phase monitoring input - it never occurred to me that this can happen.
love this guy hes through on his pathfinding to that shorted item on the board , if this was me the moment i isolated the area with shorted id be pulling out every components that beeps my tester LOL
Well as you rightly commented, it was a very enlightening video and also educational for me at any rate, I learned so much about how each component reacts with another and also how they all react or communicate with each other, a little disappointed at the end, as at the beginning you indicated that you would see us at the end which I wrongly thought was going to be the reveal of the problem and solution, I expect you will make this clear on the follow up. However I would like to thank you for the clarity in the explanation, one suggestion, I watch another channel as well and I at one point early on when you where testing the inductee coils and removed caps, I thought oh why isn’t he showing the meter, this I then noticed was on the other side of screen, so I ran back and watched, but perhaps having the meter screen or showing the meter below your face, which is where the viewers concentration is on, this and board or work piece, it’s minor but I think would really help concentration, it’s like when I used to tutor or lecture, one of the first things is don’t have any distractions in view, like a model,or piece of equipment covered or formula on the board, as it takes the students concentration from what one is trying to get them to focus on. Hey it’s not a criticism as I really do gain a lot from these wonderful and varied sessions. Or broadcasts!
Oh sorry yeah I was going to add a little 'outro' chat which I recorded and forgot to put in the edit. Oops. But I did find the actually cause of the short circuit so I hope that was satisfying.
It would have behaved same as the micro-ohm meter I used instead. The main thing here was that there were shorts on the mosfets on both phases and that made it hard to locate. Even current injection didn't work.
retired now, before finishing out my career in "IT" in the corporate world. I started out around 2000 doing home and small business networking and computer repair. we use to see puffed capacitors showing up. found out back then it was from industrial espionage where someone broke into one of the big electrolytic capacitor manufacturer network. apparently the capacitor manufacturer keep their electrolytic formula in 2 parts in different parts of their network. so the theives stole only one part. then they made counterfeit caps with forged names of good standing companies. The puffed up caps is because like i said the electrolytic formula was only half of the formula.
A master class in VRM troubleshooting, thank you Richard. As all four low-side MOSFETs are shorted, wouldn't you replace the PWM controller too? Seems like that would be the most likely cause of all four MOSFETs failing at the same time. Regards, David.
Did you listen when he said there probably would have been a short between the gates of non-paired mosfets, which made him think twice about the controller????
@@ernieschatz3783 Did you listen when he said it was very unusual for all of the low side MOSFETS to fail simultaneously? What would cause that? It was a question to an expert, not a criticism.
Here twas the regulator. Unless found when was one would never understand why this motherboard was faulty. Just inadvertent fault finding while looking at cap bases. I think that is how we normally find stuff, by accident. Wish your drawings were clear enough for me, usually can't make a firm decision from your examples because I am just too stupid and old. Funny that I would understand frequency stuffing on those inductors and fault clearing removing mosfets.
Not in this case as the low side mosfets failed, not the high side. So this would just short out the CPU Vcore supply to ground when they failed, not send 12V into it. It's unusual to find shorted *low side mosfets* but that's what we had.
Nice fault finding video but I'm pretty sure the gates on all 4 of those mosfets would have been shorted too and could have been dead easily tested in circuit?!
No the gates were not reading short. I showed that in the video. They did read like a diode junction, which is a bit odd for a mosfet gate but that could be inside the PWM driver chip as I may have been reading in the reverse polarity.
@@LearnElectronicsRepair fair enough, I heard you say you will test the gates, but must have missed you doing it. I'll look forward to the follow up, seems like as you say the PWM controller has failed and caused these to blow.