The Most Common Mistake in Laptop Repairs The shorted mosfet myth - Testing mosfets
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- Опубліковано 8 січ 2023
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I started learning electronics last year, because I wanted to start fixing faulty computers . I was eager to learn everything about electronic components, how they worked and how to find when they were faulty . And there went the magic word " shorted" 🙂, you could fix anything as long as you could find shorted capacitor or mosfet . And there I went , finding shorts in motherboards . But I quickly started to question this method of "shorts" detection
Everything is logical and understandable in Sorin's explanation. With great respect and greetings from Slovenia.
Yes that is very true. He has taught me and continues to teach me tons. No joke I think I have 60% of my knowledge from him. Would be great if he would have a class and/or forum. I am still very new to electronics and loving each step but need someone to have a Q&A with to connect the dots.
@@PapaGleb 👍Of course, I support your initiative. Sorin is an encyclopedia of knowledge and experience. We have to take advantage of that.
I'm brand new to laptop repair and you've probably just saved me (and many others) hours of effort, not to mention a few quid on mosfets I didn't need.
These recent videos are brilliant mate, thanks for helping us raise the bar, keeping more devices out of landfill.
This gentleman is very good, he should be a teacher (maybe is) , the way he can see things from both sides, through the eyes of a journeyman and as an expert. Very well done videos too with the diagrams, close ups & PIP… awesome and for FREE!!! Wow, what a gift!
@@zefdin101 Yeah he is a gifted natural teacher. I understand him and I am 30 mins into why won't my laptop power up.
"Discord" means disagreement. "Discourse" means to discuss. Keep up the excellent videos.
Last few videos are astonishingly informavive. Thank you for your easy explanation based on biginners' point of view with a schematic. Understanding how each type of compornents should behave is essential in repairing electronics.
Great video, very patient and well executed. I graduated electronics school 30years ago but I no longer work in the industry. I miss the hands on technical nature very much. You are making me nostalgic. Cheers!
Thanks for the declaration 👍 Especially the quite low resistance. Even if I know about the rules in calculating the current, I forgot, how low the resistance must be in low voltages.
Thanks alot for your time and effort to transfer your knowledge and experience 🌹🌹
Thanks for clearing these issues up.
Thanks you for sharing your knowledge Sir.
the day i learned this mosfet magic was 15 years ago or so when i was trying to diagnose shorted pentium 4 motherboard from a school computer
and the fault was complicated because it was actually shorting mosfets in pairs on 12V rail that power cpu
i broke like 8 mosfets before i came to conclusion that it isn't that, asked online for help and i was told to look for mosfet controller. i replaced that part for random part from other broken motherboard the pinout was the same and the function describtion for the chip so i swaped it, 4 new mosfets and... the board worked wierdly different than identical ones, but it works even today
with many mosfets and mosfet driver soldered like a total amateur did that with no hot air, no proper soldering iron.
but i fully admit i would be lost without help from kind people
5:30 - Heh tricky part is that some mosfets, can be activated by multimeter itself. Some multimeters on some modes, have enough volts/amps to trigger mosfet. Make a holder for smd mosfet and test it with component tester.
That is true!
Most multimeters can light up an LED on diode mode so they can activate a mosfet really easy
MOSFETs are NOT triggered by amps.
They are voltage operated devices.
@@deang5622 Good, you pay attention on classes :)
@@orion310591RS I certainly did. Rather lectures than classes.
It does of course help when you actually make a MOSFET and BJTs as part of one's lab experiments. All on the same die.
Wow, i am beginner, and these are exact steps i made when i thought i found a shorted line, or mosfet. Later on i fried the mainboard in trying to start it. How smart that you realise what would a beginner do... Thanks for the explanation
are you an expert now ? sometime the beeps don't mean the mosfet is shorted , they may come from others components on the motherboard . I haven't ordered my desoldering hot air gun yet
I’ve seen another channel using a milliohm meter to check for variations on resistance on low resistance power lines like CPU vCore power phases.
I’ve also seen people call out a short just because their multimeter beeps in diode mode.
It will beep when the reading is between 0-40 (sometimes 0 - 60) on the screen.
right! its completly wrong!
if u have a beep, then switch to ohms mode and be sure it 0...or nearly 0! then u could have a shorted Mosfet.
But only on mosfets that are "closed" if there is no power to the gate!
You should be teaching real world electronics at a major university: you´re -by far- the most clear person teaching even the basics. Congratulations, again.
Fantastic 😊 greetings from Kenya 🇰🇪
Simply beautiful explanation!
Hi Prof,very happy for yor courses,i'm in Sénégal and It's very interesting
Thank you Sorin for another informative video.
very informative video , thank u Sorin
merci beaucoup pour ces précisions
I love your new look and style, very happy and professional :)
I like "professional killer you see in movies"-look too :D
Great video, love your work.
Excellent explanation
how the powercircuit operate is very interesting! Also how a particular chip , for example the power managment chips works is very interesting for a course.. that stuff u cant find online only some given trainings..
Good explanation sir👏
I always check Gate to Ground, in 90% cases dead mosfet will be shorted on this way.
There is no ground connection on a MOSFET.
The three pins are: gate, source, drain.
@@deang5622 he dosend said mosfet has a ground he said he testing between gate pin and ground
@@mehmetbilici3612 Incorrect. He says "gate to ground". The drain pin is not always connected to ground.
What you are interested in is if there is conductivity between gate pin to source pin and gate pin to drain pin.
The oxide layer on the gate pin above the conducting channel in the MOSFET provides a high resistance path to either of the source or drain pins. But I am sure you know this
@@deang5622 İm not incorrect i said what he said.He dosent told there is a ground pin.Gate to ground main is between gate and ground.I think he checked mosfet witch is drain connected to ground.
@@mehmetbilici3612If you want to get picky on this, then I can well argue that he should have said "gate pin" and ground.
FFS. This is a silly argument. Get a life man.
Why are you so hell bent on trying to prove you are right. Do you have a mental issue?
The fact, testing between gate and ground is technically not the right thing to do. Because as I already said the drain pin is not necessarily connected to ground!
The correct way to test is as as I described.
I was hoping that my reference to how the gate sits above the conducting channel might give you a hint about how much I know about transistors and electronics.
I built a MOSFET and BJT on a silicon die
Yes, I said built.
But it seems that reference went straight over your head. And that tells me how little qualified you are in the subject.
Nice explanation great job
Very useful information. Thanks.
Great video!
Thanks
Thank you for sharing your knowledge..!!!
I remember that you told as a while ago about this confusion :) I did not forgot. And I know that only from your channel. Multumesc Sorin
Checking out what readings you get on a perfectly good motherboard will help anyone build experience and spare some of the frustration when the time comes to work on a faulty board.
Wow youre a great teacher
If you have two soldering irons available, the best way to find a shorted mosfet is to remove the inductors, which isolates the mosfets. Then you can check them individually, check each from the 12V input to each drain of each mosfet, and check from each drain to ground.
Mosfets usually don't go lightly.
great respect for this explanation. great video :)
That's a good lesson , thank you sir🙏
Thank you for showing things get fixed...
impressive info thanks sorin you are really know what you are doing , for me if i suspect in a mosfet i discharged it first , for CPU GPU circut ever 2ohms is a normal resistance .
Not that impressive when he can't get the symbol right for a MOSFET
Yes, current is moved through a cpu by switching the transistors within the cpu off and on. Each transistor has some capacitance and switching causes those capacitance to receive and discharge charge. The higher the cpu frequency the higher the power. More transistors, more power. Larger transistor geometry, more power.
good to learning tips very important one thank you sir
The laptop repair is really good and the video is excellent.
thanks sir 4 such video i am new technician from nepal and i make a laptop on shorting of resistor of charging section but over heating in first mosfect , so, specally thanks for such video.
Great class!
Thanks sir for sharing.
Thank you
LEARN STUFF - If I can do it, MAYBE you can do it too! YOU HAVE A GREAT TEACHER HERE!
Nice video, thanks for sharing it, keep it up :)
Glad I found you. Nice Person you are :)
Your teaching style is a piece of cake.
I was thinking maybe someone could create a virtual laptop repair application. To basically show a newbie how to troubleshoot a laptop you can add on schematics and so on that be kind of cool.
That would be hard to create and it would not pay you for creating it.
you buy borneo schematics
@@northwestrepairWell Well …. My other favorite Ytuber also watches Sorin 👍. Just wanted to say Hi. Sorin is the man when it comes fault finding on just any device you have.
Thanks ..im trying to test what i believe to be a shorted hexfet IFR2204S (by its distressed appearance as it looks like it was cooked) It controls a small feed motor on a 12v tennisball machine hopper ...the motor was strained due to kids overloading the hopper with balls causing very slight burning smell and then pcb control panel no longer works. I can turn on the machine but with no control functions
A point you should emphasize to your viewers , when checking resistance or continuity or anything , to always make sure the multi-meter is in the correct range. Some meters are auto ranging. I turn my auto ranging off because that feature has caused me to look like more of an idiot that I already do. Also, determine what value the meter is to for it to beep in continuity mode. I’ve had some beep but show over 10K ohms . That’ll cost all kinds of time if you’re checking a bunch of circuits for faults. Moral of the story, keep your diagnostic tools and tech(all tools and tech) in perfect working order and make yourself become highly proficient with each tool or bit of tech you own. If it’s something you use infrequently, teach someone how to use it. Oddly, teaching a topic is a great way to learn it. 👋🏼
Just lift one side of the inductor to isolate the FETs from the CPU. Then, you can check the TOTEM POLE configured FETs. One thing you did not show,!is the typical FB (feedback) circuit from the CPU side of the inductor back to the PWM that drives the FETs
we can put a resistor 10Kohm betwen gate-source to discharge capacitor gate or using totempole transistor so betwen drain-source will open soon...
Thanks Very much. Can you please explain how can we find whether it N-Channel or P-Chanel mosfet using multimeter?
Hi,
Thank you for your valuable information, do you think we can repair water damaged device which was completely under water for a while?
thanks
First time I knew this , thanks 😀
100% explanation most people they dont understand ,even also when you"re measuring capacitors around
they got same risistance from CPU you will think they are shorted
I can't wait to trigger a mosfet by rubbing a screwdriver in my hair 😃. Thank you for the video, great content!
Thanks!
sir master, idol i am learning from the scratch i am sorry telling you this that i download all your video if you would mind thank you so much i learn a alot
Good Teacher 😎
Hi, which career or online course do you recommend I study to be able to diagnose shorts on electronic boards and circuits? Thanks in advance
Sorin, I understand that the two mosfets are basically the on and off keys of the pwm controller at their gates. And yes, the lower mosfet has a lower duty cycle value so it almost never fails. But is there ANY useful information for a repairman from finding out that, say the upper mosfet is closed and the lower mosfet is open on a motherboard that is disconnected from power? Or is it a completely useless information about the state of the pwm at the moment that the power was turned off?
Thank you for a great lesson and showing the double trap in testing the mosfet without taking into account the capacitive nature of the gate and the expected resistance of the load!
Get a cheap oscilloscope and and look at the waveforms at the gate and drain pins.
Then you can test the device in circuit and actually see if it is working or not.
What you need to remember is that a MOSFET is not constructed from PN junctions like NPN and PNP bipolar junction transistors, so a multimeter set to a diode range is *NOT* the best way to test a MOSFET.
With a multimeter on diode range, you can put the PN junctions in a bipolar transistor into forward conduction or not, and yield useful information from that, but the MOSFET doesn't contain those PN junctions so this technique will not work.
Yes sir. Here is one that do like this. Thanks for this tips. Naw i learn somthing more
thanks teacher
Hi. When I become member am I going to have access to schematics? Thank you
Ciao! Bel video! Una domanda tecnica, mi sembra di capire da qualche video che ho visto di Sorin che la tensione sul gate del mosfet d’ingresso dovrebbe esssere all’incirca 25V (alimentazione + 6V) per garantire che il mosfet è in completa saturazione per evitare che l’eccessiva resistenza causi temperature che a lungo termine danneggiano il mosfet.
Sono 19V sul gate abbastanza per il mosfet? Scusa se la risposta è ovvia.
there is something important on Mosfets....is it a NPN or PNP!
of couse u have a "Short" on a good mosfet.
some Mosfets are open without a charge and the other are closed without a charge! only the Charge is the Factor in this cases!
on top of that: You cant check components in a circuit! You have to desolder it, to be sure!
and please do not test mosfets with beep/diode mode! if u have a beep, that is not a meaning of a "Short"
How to know if is pnp or npn
in many cases, you look at the last digit in a mosfet model number. If not then you google it. If still no idea you do a quick test for polarity.
@@suediem9315 Polarity?
there is no "Polarity" on Mosfets!
They have no ground!
i guess u use the wrong meaning!
@@jpius1017 sorry but YT delete my first answer of your question!
use google!
everybody say if you have continuity between gate and source (8 pins mosfet) that means the mosfet is bad
its a case of other components making a component appear shorted, . its a usual case . never assume that a component that reads short is shorted as it maybe connected in parallel with other components giving misleading result . Yes it can make things hard, Thats where a good knowledge of how your circuit works is handy. Great video which demonstrates this , but sometimes i wish you could improve your English as i find some words are not clear .
please sir reply me, What should be the value if the gate pin and source pin of good mosfet are supplied with power and measured with a multimeter?
Great video :)
So many times I have fallen on that mistake, now I know
thanks !!
U can use diode mode multimeter to charge mosfet gate and test it, no other equipment needed. :)
Sometimes multimeters don't have enough voltage to turn it on.
Hi sir can u make laptop repairing basics video pld
Very Good
I've learnt this hard way, short is zero ohms nothing else, when in doubt, beep should be held for at least 2 seconds to see if value is not changing (Capacitors), you can do the same with resistance meter.
Sorin, thanks a lot ! But , I never hear about the internal diode of the mosfet which can conduct in one direction also with the forword voltave of the diode, am I right?
Thats the difference between a P-Channel and a N=channel MOSFET.
wow just join the discord and there is a lot of PDF book to read from there, nice community❤
I understand what not to do ... so how I should test the mosfet? Should I necessarily removed it from the board to test it with a resistor or its not neccessary?
You know so much that you don't even imagine what we don't know.
Yes. I'm still getting confused. While the FET and CPU hasn't caught me (I think?) I still can't figure it out! 😆
Hi Sir can you please help us on what is Vcore and how it work and how does it affect to make a computer or laptop to display
VCORE is the CPU power supply. It is usually a multiphase switching regulator.
Basically, some shorts are shorter than others.
Sorin, and that's mostly when you have a very low voltaje line, so that line its 1 volt.
Sir, if the mosfet has been replaced many times, it still shorts out again, which part should I recheck... I'm repairing a Biostar B250 GT5 PC motherboard... Thank you in advance if you want to answer... I'm a beginner technician.
Hi. You sound like you know a lot about a PCs. I have a Motherboard with no Manual for it and it's not available on line. My header has 10 Pins unmarked. Can you please tell us how to identify Front panel Pins using Multimeter or any other technic without damaging the board. Thank you.
I'm totally new to this kind of stuff. I did not fully understand but i understood the rookie mistake thinking it's Moffat
when it's not. I will re watch and hopefully things will sink in more :)
This just happened to me. Now I want to remove the other MOSFET. I just hope the CPU is not the faulty component
so how do you check a mosfet? Or is the point that you usually don't need to?
mis mosfet sueltos en el escritorio te lo agradecen 😆
How do you know which is the gate on the mosfet ?
I had a cpu that showed 0.0 ohm on vcore with coil removed.
I injected 0.8 volts and increased the current it took up to 6 amps then my probe leads got warm but nothing else.
Does that mean that the cpu is bad?
I tried the same thing with a different board and the cpu took about 2.5 amps and got slightly warm.
Is it ok to replace an 8pin mosfet with any kind with the same shape and size?? (Is there a consideration of numbers or codes)
The Mosfet is burned and cracked.
Yes that what s we need
as a beginner
Thinks
Mr. Sorin, you did use a resistor to short the gate with the source (or drain)? It’s not very clear on the video what you have in hand. That’s a resistor, isn’t?
Thanks
You can use anything conductive to short the gate with the source.
Mosfet in circuit is always a problem.
Maybe voltage injektion is better
But only 1 volt and 2 to 3 amps with a power supply
No.
1 volt is not enough.
You need to need to look at the turn on or turn off voltage for the gate pin, known as VGSON or VGSOFF of the particular type of MOSFET used. Just as an example there are so called logic MOSFETs which are compatible with digital logic and have a VGSON voltage of 5 volts. For these 1 volt will not be high enough.
Don't make assumptions. You are likely to be wrong. Look up the required data in the datasheet for the transistor.