Asus VG278 mosfet identification ?

[guizmo1967]

Hello,

My Asus monitor stop working today !! I found the problem on the main board, the power supply board is ok. It's Q9, a mosfet but I have no idea what are the specs since I don't have the schematic for that monitor !!

Can someone help me identified this mosfet ?

Thank you !

[прямо]

Measure the voltage at the GATE (G) and SOURCE (S) pins.

[guizmo1967]

Thanks for your reply !

But I figured it out by myself. Q9 is a P-channel mosfet that only switch positive voltage to the connector (I think it's 12V). The gate is pull high by R151, so mosfet is OFF and pull low by NPN transistor Q10, mosfet is ON.

I removed Q9 and check every components around that mosfet and they are all OK.

Unfortunately I don't have a sot-23 P-channel mosfet lying around right now !!

If I'm wrong, don't hesitate to correct me .....

Thank you.

[прямо]

Nope, you are correct that it is a P-channel mosfet.

[lotas]

Mosfet

[momaka]

With that MOSFET is burned the way it is, check T-con board for short-circuit on the 12V rail that goes to the T-con board (the board attached to the TFT screen with film cables, usually) and all of the secondary voltage rails on the T-con. Chances are that MOSFET blew up because something on the T-con shorted. Pictures of the T-con would help further throubleshooting. Generally, the secondary voltage rails on the Tcon are AVDD, VHG, VGL, VCOM... and a few more. They are labeled with round test points usually. IME, any of these rails shorting has been due to a shorted ceramic cap somewhere. If you are lucky, you might see an overheated ceramic cap somewhere. If not, it's going to be a bit of a hunt, but not too hard to do.

I repaired an old 17" Dell monitor like this many years ago. Found the shorted ceramic cap and got it replaced. The P-ch MOSFET on the logic board was also destroyed in my case. Not having any on hand, I bridged it (Source & Drain pins) with a piece of solder. The effect of that is the monitor will consume a few more Watts of power in stand-by mode (since the T-con board won't be turning off, ever)... but it's a workaround if you can't find a P-ch MOSFET.
Don't bridge your MOSFET before finding out what caused it to burn out, though. Otherwise, you'll probably end up with more parts damaged / in need of replacement.

[SMDFlea]

Maybe its Sinopower APM2309AC-TRG

https://world.taobao.com/item/wap/561284180463.htm

Datasheet https://datasheet.lcsc.com/lcsc/1806...RG_C207580.pdf

[guizmo1967]

The 12V rail that goes to the T-con is indeed shorted ! There is a lot of capacitor on that board and none are overheated. Don't want to remove capacitor randomly, can you suggest me a way of doing this, not randomly ?

Maybe voltage injection ?

Thank you

[lotas]

Have you tested with the lvds cable disconnected? Disconnect the cable and apply a small voltage from the laboratory power supply (5-10v) and adding amperes (1A +) you can find that there is a short (find the culprit) on this bus. You just need to know exactly what voltage the panel (matrix) is powered at - some are 5v, some are 12v!

[guizmo1967]

Yes tested with cable disconnected. I connected back the power supply to check what was the voltage at the Source of mosfet Q9 (Of course removed) and it is +12V. Should I start with +3V, 1A or go with +12V, 1A ??

Right now I'm searching online for every IC's on that board to find Vcc pin to make sure none of their power rail is shorted before injecting voltage ....

[momaka]

The 12V rail that goes to the T-con is indeed shorted ! There is a lot of capacitor on that board and none are overheated. Don't want to remove capacitor randomly, can you suggest me a way of doing this, not randomly ?

Maybe voltage injection ?

Thank you

Could you post a better picture of the area with the SMD inductors on the T-con?
I see about 8 ceramic caps connected to the input 12V rail after the fuse.
It could be that those are bad or it could be a shorted MOSFET (or T-con inverter IC has built-in MOSFET?) on the AVDD rail... or shorted ceramic cap + rectifier diode on the AVDD rail.

Voltage injection might or might not work too well. Ceramic caps often do a "hard" short-circuit, acting like a piece of wire. So finding the bad one with voltage injection may get tricky. Of course, if you're experienced with doing this already, then do try it. I prefer to tackle T-con problems like that with the soldering iron: big fat tip + a bit of flux, and I can get most of those SMD caps removed in no time. I don't do hot air because of the proximity of the bond cables, which can get damaged by excessive hot air.

[lotas]

In such cases, a milliohm meter helps a lot, where there is the lowest resistance on the components, that is the culprit.

[guizmo1967]

I found the problem. I injected +2V, 1A. The area circle in red what getting really hot to the touch, so I thought it was one of those two capacitors. I removed them one at a time and check if the short was gone but no !

Did voltage injection again and it was Q308 that was getting hot !!! Removed that transistor and the short is gone. Soldered back both capacitors and everything is good.

But I think it should be a transistor not a mosfet since there is no G D S markings ?? What do you think.

[guizmo1967]

After further investigation, I think it's a SOT-23 NPN transistor. The bottom left is B. bottom right is E and top leg is C.

With no power to the board, the two bottom legs are GND. R302 (Mark 203) keeps Base to ground, transistor OFF.

This transistor is switch ON by AUO-P303-19.

[lotas]

After further investigation, I think it's a SOT-23 NPN transistor. The bottom left is B. bottom right is E and top leg is C.

With no power to the board, the two bottom legs are GND. R302 (Mark 203) keeps Base to ground, transistor OFF.

This transistor is switch ON by AUO-P303-19.

This is mosfet P5002CMG https://aliexpress.com/item/1005003351009366.html

[guizmo1967]

Thank you lotas !

Yes after searching the internet, it is a mosfet. Either P5002CMG like you suggest or AO3400A would do the job !

[lotas]

Thank you lotas !

Yes after searching the internet, it is a mosfet. Either P5002CMG like you suggest or AO3400A would do the job !

Yes, it is even more powerful than the original, as long as the chip is not damaged.

[guizmo1967]

I'm going to try finding a mosfet with marking 12H34 on one of my laptop motherboards that I keep for parts and bridge SOURCE and DRAIN of the P-channel that I don't have yet and see if the Asus logo appears on the screen ??

[guizmo1967]

Yes, it is even more powerful than the original, as long as the chip is not damaged.

Well no luck !! I solder a AP2334GN-HF in place of Q308, put a jumper between Drain and Source of Q9, plug everything back together and no Asus logo ...


Before I made any changes, the screen was always white and now when I turn it on, it goes white a second, then black a second, and white again before stand by (amber light)



I think AUO P303-19 is bad ??

[guizmo1967]

Can someone tell me what is exactly Q302 (W1 marking), another mosfet and if so, part number would be appreciated !

Thank you !