I am new to electronics and I'm understanding most of what I'm reading but I have a mosfet on my board that I've identified as a P-channel Trench Mosfet. I haven't a clue how to test this and what I should expect to see with the multimeter probes. I am hoping someone with years more experience than myself can help me understand how to use a multimeter to read this. Please look at the drawing I have attached to this and can you try to explain to me what I should be doing with my multimeter in diode mode and what results I should expect from a good mosfet?
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If I am reading this properly and in diode mode, putting your black probe on Pin 3 Drain and Red Probe on Pin 2 Source you will get nothing. Put your black probe on Pin 2 Source and your red probe on Pin 3 Drain you will get a reading perhaps in the 500 range. If you put your black probe on Pin 1 Gate and your red probe on Pin 2 Source you will show a short the way it looks to me and your beeper will sound on your meter, and vice versa put your red probe on Pin 1 Gate and your Black Probe on Pin 2 Source again you will read a short and your beeper will go off. Is my interpretation of this Mosfet correct? It's weird because on the gate and source pins all you can see are the anodes and the cathodes seem attached internally inside the mosfet. This truly has me stumped. I'm sure an engineer will know how to interpret this chip. -
If I am reading what you wrote then what has happened you turn on the mosfet to conduct the flow of current source to drain you should be able to turn it off again and you should get the same results you did when you first started checking it
I personally have not tested mosfets very much so I can not tell you accurately how to turn it offComment
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Correct.
With that test, you're essentially reading the internal protection diode between the Source and Drain pins (and also confirming that Source and Drain are not shorted together). For N-ch MOSFETs it's the same, but with probe polarity reversed to what it is for P-ch MOSFETs.
No, it's usually bad news for the MOSFET any time you get continuous beeping on your meter (indicating short-circuit / low resistance / low voltage drop) between Source and Gate, regardless of the probe orientation - at least if testing the MOSFET out of circuit. In circuit, there can be another component interfering with the measurement, so the MOSFET may not necessarily be bad... though in most cases, beeping between Gate and Source in circuit is also still indicative of a failure.
I haven't looked at this particular MOSFET's datasheet yet, but those are probably Zener protection diodes on the Gate.
Continuing with the rest of the tests for this MOSFET...
If you put your red (+) MM probe on the Source and black (-) MM probe on Gate, then move the black (-) probe to the Drain, you should now see a low voltage drop / low resistance / your multimeter continuously beeping to show continuity, as this charges the Gate, which opens the conduction channel between Source and Drain (for current to flow.)
The above is applicable to P-channel MOSFETs only. For N-channel MOSFETs, the test is the same, but with the MM probe polarity reversed (i.e. red on Gate and black on Source, then move red on Drain, and you should get beeping). And of course, worth noting that this works only for MOSFETs out of circuit. In-circuit, there will usually be a discharging / pull-down resistor between Gate and Source, so this test won't work there.Comment
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Thank you for your input and for clearing some of this up for me.
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Hi, i am noob in repairing electronics and motherboards...and most of the time i am still trying to understand how things work...So, lately i have been using and testing motherboards in diode mode. Most of the motherboards that i test are not working and broken. The question is that if i use multimeter in diode mode on high 19vol rails sometimes i read fixed number in multimeter but on some other boards reading in diode mode is rising indefinitely till i read 1. I am talking on lets say ac_bat 19volt rails on motherboards. So, i dont understand how it is rising indefinitely? In theory if only... -
Hello everyone, I recently found this badcaps site and super Learn Electronics Repair youtube channel. And I wanted to learn how to troubleshoot power supplies and VGA cards and how to practice soldering, since I already have a properly defective piece of them. I am currently trying to solve two problems:
I have a Gigabyte GV-RX460WF2OC-4GD type card. I managed to find the faulty MOSfet (AON6414A) on it, which I replaced. The card starts up, but after about half a minute, the MOSfet in the same position will be shorted again. Is it possible that the PWM controller driving the MOSfet... -
I tried to use this method:
Testing an N-channel MOSFET:
Step 1: Discharge the Gate (turn off the MOSFET)
Place the black probe (COM) on the Source (S) and the red probe on the Drain (D). The multimeter should show no continuity (high resistance or "OL" – open line).
Then, touch the black probe to the Source (S) and the red probe to the Gate (G). This discharges any stored charge in the Gate, turning the MOSFET off.
Step 2: Charge the Gate (turn on the MOSFET)
Now, place the red probe on the Gate (G) and the black probe on the...09-27-2024, 03:31 AM -
Hey guys,
i have a asus motherboard here and as the title says after the first mosfet (in the picture) there is nothing more than 3.15v.
I injected 19v and max. 1 amp at the charging port and there is not voltage drop or smth. It's just taking 19v and 1 milliamp.
Then i tried to inject 19v and max 1amp after the current sensor and there it first takes 19v and 4 milliamps and after 2 seconds it is taking nothing (no current).
I measured on the coils on board everything seems fine. Also the main power rail is not shorted (infinite resistance).
Now i thought something... -
The board number is GU502DU. I repaired this a couple weeks ago and it came back with the same issue, same mosfet failed (PQH9201). I'm hoping that the GPU was spared this time.
I used the same replacement part (purchased from Mouser) and I'm certain the soldering was done properly since it took just as much effort to remove as before. What could cause this same mosfet to fail? I'm thinking if it was unsuitable then the others would fail too. I looked for similar failures on YTube and the mosfet was replaced with AOE6930 in one instance and AOE6932 in the other but it's possible that the...
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