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Identifying and Replacing component "Q9" on Asus VG278Q

Part closeup

https://imgur.com/a/IAa92ta

Board itself

https://imgur.com/a/d4hkzME

I have an ASUS VG278Q 27" 144Hz gaming monitor that recently crapped on me.

I've found the part that failed but am having difficulty identifying a part number. Haven't had any luck looking up part numbers through googling.

This form factor tends to be a MOSFET, voltage regulator or diode . I'm guessing transistor based on the Q9 reference designator but then it makes me wonder what kind? NFET or PFET? Or even BJT?

The only things I can seem to make out are "21..."

Any suggestions on how to find the replacement part?

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Hi! How did you disassembly this monitor? I am trying on mine but a black tape is hard attached to the bezel.

von

It is really frustrating to try and disassembly it. There are some kind of tab/hooks that hold the frame together. You need to put a thin spudger to put pressure and widen the gap until the hooks undo themselves.

I'm not sure what tap you're referring to

von

Hi moybryan3. Sorry, i meant "tape", black tape.

von

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Have you tried looking for a replacement board? There is a board number usually printed on the PCB.

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Unfortunately couldn't find a single vendor that sold the board.

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Hi friend, this is the Q9 component.

https://imgur.com/RCT0Wpo

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Awesome that you got me that picture. Unfortunately shorting drain to source of that "FET(?)" didn't work and neither did using an alternative part so I'm out of ideas since it is two nested FETs and controlled gate by the center CPU. The power rails looked good but I just keep getting white screens.

von

Hi moybryan, this is what I found on my board (Asus VG279Q) its almost the same layout:

https://imgur.com/a/hm9Vq1x

Q9s marking is: 21J19

Hey btw. do you still own the pcbs? Because I got a blown resistor on the power board and I can't read the marking any more... would be awesome!

von

any luck with fixing it ? i have the same issue, got another main board and it blew again :(

von

@cabe94 Power supply board defective perhaps?

von

Unfortunately I wasn't able to fix it. It's sitting in storage until I have a stroke of genius or one of us figures it out. The power supply measured proper voltage on my meter. I measured the power rails on the board itself and had no luck.

I tried to just bridge the SD connection ignoring the gate but had same result. I'm expecting that something else is the cause and didn't want to go down this rabbit hole any further

von

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Hi,

Here’s a link to a supplier of mainboards and other major parts for the monitor.

There are two different models i.e. VG248QE and VG248QG.

Click on the appropriate model number and then click on the mainboard entry to see details regarding the Asus part number. If you search online using the part number only there are other suppliers or just use the supplier linked.

Did you try searching for the board number schematics? My eyes are gone even when zoomed in I can’t make out more than 4H 3QTG4.A00 but I’m not confident that this is correct as nothing even remotely shows up when searching using that number or other close variations

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Hello, I just now had success getting my 278Q working again! Here is what I did. Inspired by a youtube video (search for 278Q whitescreen) I first looked at the fuse and MOSFET on the LCD board. The fuse was not blown but the MOSFET seemed to be bad (though not visibly blown). I did not have a tiny surface mount replacement MOSFET so I instead soldered very fine wire wrap wires onto the three pads and fed that out to a large, discrete IRF540N MOSFET. This may have been necessary for the repair but was not sufficient. I tested power on the LCD board at the 12V test point and it was 1.1V. (I should have done this first.) Then I opened up the main board behind the metal shield. There was an obvious visibly blown component in the same spot as the initial post on this thread (Q9). I cleaned that away and again soldered fine wire wrap wires to the three pads and fed those to another external large IRF540N. To my great surprise, no more whitescreen of death, and the ASUS logo came up!

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Hello Rick. Congrats on the successful repair. I'm having same problem but no visible damage anywhere.

Could you please let me know where the 12V test point is on the LCD board? Can't seem to find it anywhere.

Thanks in advance.

von

On the underside (non component-side) of the LCD control board there is a pad marked "12V" very near where the flat cable comes in. The LCD control board is the wide board that goes along the bottom of the monitor, it is not one of the boards inside the shield. For the other (ground) reference, use the bare copper along the bottom of the board. Between those two points should read close to 12V. Also test the continuity on the little fuse on the component side (it should not be blown, obviously) and also test for shorts on the MOSFET on the left side of the board. On my monitor the fuse was intact but this MOSFET was bad (in addition to a MOSFET on the power supply). Those are the two MOSFETs I replaced with IRF540Ns. The MOSFETS I used came from Amazon in a package of 50, 5 each of 10 types, for about $8.

von

To clarify, the MOSFET on my LCD board was bad but not visibly damaged while the MOSFET on my power supply board (Q9, image at start of this thread) was blown to bits and the whole vicinity was blackened but could be cleaned up. Also I looked and the 50 MOSFET assortment that I got on Amazon was $18.99 not $8.

von

Thank you again and for taking the time to reply! No visible damage on any of the three boards and the fuse tests fine. MOSFETS also appear fine, but testing them in circuit so not sure. I'll now check the 12V as you mentioned. I found the two main boards behind the shield for sale on ebay for $20; if I can't pinpoint the issue, might just take a chance and replace these in hopes the issue is in one of them. THANKS AGAIN!

von

[Rich, not Rick... apologies ;) ]

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Hi,

This might be the component that you are looking for.

Block Image

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thewinklesnail wird auf ewig dankbar sein.
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