Duff 28" ASUS PB287Q 4K monitor

[wizpip]

how old is it?
ASUS usually has a long warranty - 3years or more

Well, that's a story. Bought it from Amazon and apparently via a seller. When it died Asus wouldn't talk to me because the serial number wasn't from the UK. Amazon wouldn't talk to me because I'd bought it from a seller. The seller wasted two weeks of my life saying they'd arrange to have it swapped with an open box one they had, before deciding that it didn't actually exist. They issued me a refund and then I spend a few months emailing both them and Amazon asking them to take it away (because you know, it would have been in warranty somewhere!)

It was only when it became apparent that there was going to be no further contact that I decided to take it apart. Given that the backlight works (by hacking it internally) and the monitor was powered but off when it died, and Windows no longer realises that it exists, it's fair to assume that the logic chip gave up on life. I tested pretty much every exposed component on that board and everything seemed fine.

Asus don't sell the internal boards individually so I have a saved eBay search waiting for someone with a cracked panel. It'd be a shame to put what's probably a perfectly good 4K panel to bed before it's done its time!

[stj]

that's revealing.
if the pc cant see it then it may be simple.
the pc uses the ddc serial lines to read an eeprom in the monitor.
so maybe the eeprom is toast, or not getting power, or the cable/connectors are at fault.

[EHT]

Just to be clear, when you force the PSU's ON/OFF line to ON, is the backlight on and the video signal displayed fine?

Nope, there's no response from the panel at all.

OK, the first task is to determine if it is a PSU or logic board fault. If you did as I described above and the backlight does not come on then it would be a PSU fault.. unless there are other such control lines. There was one next to ON-OFF that I couldn't read. In a similar monitor I recently fixed it had 3 lines:
- ON-OFF - turns the PSU on, overall (enables the PFC converter)
- BL_ON - turns on the backlight (monitor does this with a delay from above)
- Brightness - PWM signal for backlight brighness (not really relevant as even lowest, the LEDs are visibly on)
^ check for the above. If only ON-OFF, looks like a PSU fault. You would need to investigate the circuit a bit and see what type of controllers are used. Look for the type numbers and then Google to find an example circuit in the datasheet. You could blindly replace the 2 or 3 controller ICs as these are probably really cheap parts.

[wizpip]

Just to be clear, when you force the PSU's ON/OFF line to ON, is the backlight on and the video signal displayed fine?

Nope, there's no response from the panel at all.

OK, the first task is to determine if it is a PSU or logic board fault. If you did as I described above and the backlight does not come on then it would be a PSU fault.. unless there are other such control lines. There was one next to ON-OFF that I couldn't read. In a similar monitor I recently fixed it had 3 lines:
- ON-OFF - turns the PSU on, overall (enables the PFC converter)
- BL_ON - turns on the backlight (monitor does this with a delay from above)
- Brightness - PWM signal for backlight brighness (not really relevant as even lowest, the LEDs are visibly on)
^ check for the above. If only ON-OFF, looks like a PSU fault. You would need to investigate the circuit a bit and see what type of controllers are used. Look for the type numbers and then Google to find an example circuit in the datasheet. You could blindly replace the 2 or 3 controller ICs as these are probably really cheap parts.

I'll have to get back to you later on this - it all happened quite a while ago and it's currently packed a way. One thing I will say though is that the monitor backlight and display should come on without any signal connection at all to flash a big ASUS logo across the screen, followed by no signal, and then standby. I've attached as far as I bothered to trace on the PSU - yellow is 18V, red 5V, black ground.

[stj]

that's the most incredible pcb foto i'v ever seen!!

there are some early signs of failing solder joints on it - and i'v only looked at the lower 1/3rd !! 

[wizpip]

that's the most incredible pcb foto i'v ever seen!!

there are some early signs of failing solder joints on it - and i'v only looked at the lower 1/3rd !! 

That's probably my fault - I desoldered a lot of things to test them! Didn't do a particularly good job putting it back together...

[stj]

no stress cracks, faint rings on some of the factory joints.

[EHT]

Yes, very good picture! If the backlight is coming on with or without forcing ON-OFF then I'd say it isn't a PSU fault.

If the backlight doesn't come on when forced then investigate the PSU. Look for the model number of U801 and IC901, then look up the datasheets via Google to find an example circuit which will probably be very close to that in the monitor (assuming there is no service manual / schematic).

[cirthix]

You say you measured 18v to the panel? 

That would be bad.  M280DGJ-L30 uses a 12V input.

There should be an 18v to 12v dc/dc converter on the main board.  This is probably shorted out.

Feeding 12v to the tcon will probably fry it too.  Depending on what went wrong, the panel itself is probably OK.

This is a normally-transparent panel, so if the tcon is fried and the pixels aren't being driven, it will appear all white.

But you say you see a logo flash, so it must be at least sort of ok.  Maybe you measured wrong?

[wizpip]

You say you measured 18v to the panel? 

No - there's no voltage to the panel at all. When I short the on pin to 5V pin on the power board 18V flows to the backlight, causing it to display bright white. The datasheet for the panel lists the backlight voltages as: Min -, Typ 37.2, Max 39.6

That would be bad.  M280DGJ-L30 uses a 12V input.

For the LCD part, not the backlight. As I noted originally, there's no voltage over a few mV on the TCON, either in or out.

There should be an 18v to 12v dc/dc converter on the main board.  This is probably shorted out.

Main board - the logic board? Any idea which one it'd be from the pic?

Feeding 12v to the tcon will probably fry it too.  Depending on what went wrong, the panel itself is probably OK.

This is a normally-transparent panel, so if the tcon is fried and the pixels aren't being driven, it will appear all white.

But you say you see a logo flash, so it must be at least sort of ok.  Maybe you measured wrong?

No - the logo is supposed to flash on a working unit. Nothing happens at all on this one, except for a white power light which is always on.

[cirthix]

In that case, check this 12v regulator

[GraXXoR]

I know this is a total necro, but I have had exactly the same issues on my faithful PB287Q... It had been working 100% well and then suddenly, while I was watching Youtube... Sudden white screen.
It then switched off and now when I power it up, I get the white power LED and a white screen for a few seconds, blackness and then as if it's making a second attempt, another white screen for a few seconds... The screen goes out and the power LED returns to Orange, sleep mode.

In my case, there is not a hint of any logo or any other image... But I didn't try to short or cut anything while I had the screen open.

I actually opened mine up expecting to see some duff caps, and put a photo of the board into Google image search. That is when I found this thread.

Does anyone know what happened? I guess I'll just auction it off as a working panel. WHich is a shame because the panel is still totally evenly lit without any yellowing around the edges. It honestly looked as good as the day I bought it nearly 10 years ago, a testament to the quality of the panel they used.

In any case, any help much appreciated. I'd really hate to throw out a screen that is otherwise pretty much in mint condition.

[tom66]

White screen suddenly happening sounds like the 12V/15V supply to the T-CON has disappeared, I second the suggestion by cirthix to check that DC/DC converter.