Looks like a surface-mount transistor

ShovelKnight wrote on 2020-05-19, 17:41:

Looks like a surface-mount transistor

Yeah, I think that too. I've found on the board another Q37 component that looks the same, has a code but is so difficult to read, I'm trying to read it..

EDIT: Q37 near to the SATA ports has a "K72 N2" code on it!
EDIT2: There're different version of similar components with different codes but the closer one the Q37 but also many others seems to have the same "K72 N2" code. Looking around I think maybe it should be the 2N7002 N-CHANNEL ENHANCEMENT MODE MOSFET of Diodes Incorporated company and that N2 number should be the year 2002 and the month February.
I can't be sure without a confirm of someone having the same board but I suppose it may be it the component to buy and solder. Any more idea?

Hi,

According to a boardview for a similar model the Q38 is a P-mosfet AP2309GN manuf. APEC
Datasheet

The purpose of this mosfet is to send +5VSB when the mainboard is turned off. The Q41 is N-mosfet and it does the same for +5V when the mainboard is turned on. They both are controlled by +12V on their gates (of course through the resistor).

Roman555 wrote on 2020-05-19, 19:31:

Hi, […]
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Hi,

According to a boardview for a similar model the Q38 is a P-mosfet AP2309GN manuf. APEC
Datasheet

The purpose of this mosfet is to send +5VSB when the mainboard is turned off. The Q41 is N-mosfet and it does the same for +5V when the mainboard is turned on. They both are controlled by +12V on their gates (of course through the resistor).

Thanks. I already tried to change it but the problem seem to be deeper than the package itself basically destroyed just as long as I tried to desolder it and solder pad seems to be a bit difficult now to solder. Still I've put inside a K72 similar mosfet of another mainboard but it can't boot anyway (cpu fan runs, chipset got warm etc but no beep no video). Maybe I ruined the mosfet before desoldering from the older mainboard so I'll try again in these days as soon as I'll get the new ones but I miss the tools for this kind of smd soldering.. 🙁 I'll update this soon!

Q37 is really a N-MOSFET 2N7002K. It can't work instead of Q38 because Q38 is a P-MOSFET.

Roman555 wrote on 2020-05-20, 04:35:

Q37 is really a N-MOSFET 2N7002K. It can't work instead of Q38 because Q38 is a P-MOSFET.

I knew that I wasn't lucky to try with that.. anyway I'll try desolder it again and find that one.

Update: things are getting bad... I think under the p-mosfet there was serious glue that make it hard to remove and I may have lost the left low pad to solder...this smd should be desoldered with the hot air specific tool I don't have.. 🙁
Where the left point may end up on the mainboard? [ERROR]From the datasheet of the p-mosfet above that should be the Ground, shouldn't it? Could I take a ground point somewhere else to solder the p-mosfet?[/ERROR]

386SX wrote on 2020-05-20, 14:30:

Update: things are getting bad... I think under the p-mosfet there was serious glue that make it hard to remove and I may have lost the left low pad to solder...this smd should be desoldered with the hot air specific tool I don't have.. 🙁
Where the left point may end up on the mainboard? From the datasheet of the p-mosfet above that should be the Ground, shouldn't it? Could I take a ground point somewhere else to solder the p-mosfet?

I think It can be repaired. Also you have to do soldering works using a soldering iron with narrow tip.
I'll write you later about left point of the mosfet (the left pin is called GATE). I don't have access right now.
But if you have a multimeter you can make some measurement and you'll understand where GATE should be connected. I gave you the clue early. Of course it shouldn't be the Ground rail!
Both GATE of Q38 and Q41 are connected together. So just find out what pin of a resistor bellow Q38 is connected to Q41 GATE. I think it's the left pin of the resistor but I'm not sure.

And there are desoldering techniques without hot air

https://youtu.be/CVsmwFAkf7I

Roman555 wrote on 2020-05-20, 15:34:

I think It can be repaired. Also you have to do soldering works using a soldering iron with narrow tip. I'll write you later abo […]
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386SX wrote on 2020-05-20, 14:30:

Update: things are getting bad... I think under the p-mosfet there was serious glue that make it hard to remove and I may have lost the left low pad to solder...this smd should be desoldered with the hot air specific tool I don't have.. 🙁
Where the left point may end up on the mainboard? From the datasheet of the p-mosfet above that should be the Ground, shouldn't it? Could I take a ground point somewhere else to solder the p-mosfet?

I think It can be repaired. Also you have to do soldering works using a soldering iron with narrow tip.
I'll write you later about left point of the mosfet (the left pin is called GATE). I don't have access right now.
But if you have a multimeter you can make some measurement and you'll understand where GATE should be connected. I gave you the clue early. Of course it shouldn't be the Ground rail!
Both GATE of Q38 and Q41 are connected together. So just find out what pin of a resistor bellow Q38 is connected to Q41 GATE. I think it's the left pin of the resistor but I'm not sure.

And there are desoldering techniques without hot air

https://youtu.be/CVsmwFAkf7I

I feel sad to look how easily he did in that video, I mostly soldered old type of components and never needed that, I probably should have waited a bit more for a easier removal. Thanks!

So yes, left pin of the Q38 should be connected to left pin of the resistor

Roman555 wrote on 2020-05-20, 16:06:

So yes, left pin of the Q38 should be connected to left pin of the resistor
mainboard3.jpg

Great. I was testing as mentioned that these are in fact connected. Maybe at the end it will not boot anyway but again, thanks. I'll look for the same or an equivalent SOT23 p-mosfet I think there're different package codes for the same AP2309GN. 😀

386SX wrote on 2020-05-19, 17:07:

Hi,

It's a long time I've this mainboard (FM2A55M-DGS rev 1.02) and never understood why it could not post; I tried cpu, rams, a new bios eeprom and at the end it became a personal quest to try understand the problem. At the end I think I found it: close to the ATX connector there's this component I never noticed it's sort of broken who knows what happened. I have already spent enough into this and I think I may replace it myself even if it's really not as big as it looks like so it's going to be difficult but the main problem is that I've no specifications or info about what was it in the first place. Have you any idea? If I think to all the time spent into the "usual" no-posting problems when most probably that may be THE problem...

Thanks!

here is a link to a place where members share technical layouts of motherboards showing capacitor, MOSFET, diode values I mean, MOSFETS can look like transistors or power regulators. https://www.badcaps.net/

zapbuzz wrote on 2020-05-21, 07:49:

here is a link to a place where members share technical layouts of motherboards showing capacitor, MOSFET, diode values I mean, MOSFETS can look like transistors or power regulators. https://www.badcaps.net/

Thanks. I'll look for that mosfet having same or similar compatibility. Of all the mainboards broken I could have take it from, it seems none are p-mosfet. I'll search there for more info but thanks to the great earlier advices above I have the right direction to look for the solution! 😀
Not that is important this mainboard, I got it as untested and FM2 cpu support is quite limited but at this point it's interesting to see it booting. 😉