Author Topic: Duff 28" ASUS PB287Q 4K monitor  (Read 5791 times)

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Offline wizpip

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Duff 28" ASUS PB287Q 4K monitor
« on: April 24, 2017, 01:17:52 am »
So I went on holiday for a week and when I came back my monitor wasn't working. When plugged into power the monitor's power light turns on (white) and stays on. On a working monitor this would change to orange as it went into standby. There's nothing from the display at all - no backlight, and as far as I can tell no pixel manipulation either. Windows doesn't detect the display when connected.

I opened it up. There are no blackened, bulging, or cracked components. I desoldered and tested all of the electrolytic caps on the power board to be sure - they're fine (forgive my dodgy resoldering work). The power board has a 5V labelled connector heading to the logic board - this gives a solid 5.28V on my oscilloscope. There's also an unmarked yellow wire putting out 18.4V to the logic board - also solid. There's a secondary connector going to the LCD panel itself - most of these pins read a low mV value except for ground pin 6, and pins 3 / 4 which have the same 18.4V.

There's a 1AMZ chip on the bottom of the logic board - one of these legs is 3.2V solid.

The t-con board has low mV values for all of the non-ground places I probed.

Disconnecting everything but the powerboard showed 1W of usage on my socket monitor. Plugging everything in showed 6W - so something's using some power.

Power board: 715G5665-P01-001-003E
Logic board: 715G6681-M02-000-005I
T-con board: InnoLux V390DK1-CLS1

Any insight you can give me on what to test or do next would be much appreciated!
 

Offline Rasz

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #1 on: April 25, 2017, 12:46:43 am »
shooting in the dark - whats on the brown wire? maybe its power good and its not good keeping controller board in permanent reset?
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Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #2 on: April 25, 2017, 05:45:15 pm »
shooting in the dark - whats on the brown wire? maybe its power good and its not good keeping controller board in permanent reset?

Labelled as On/Off and has a constant (slightly noisy) 72mV...
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #3 on: April 25, 2017, 06:56:49 pm »
The last wire is orange, labelled DIM, and gives a square wave 240Hz between 3.3V and 120mV. I haven't found a specsheet for the board (and ASUS won't help) so I'm not sure if this is right. Unless someone can tell me if this is right or wrong I'll try to work the circuit back and figure it out, eventually! The one thing I will say is that 240Hz isn't a natural multiple of anything - my household supply is 240V @ 50Hz, so 240Hz is being generated by something other than the mains...
 

Online james_s

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #4 on: April 25, 2017, 07:37:01 pm »
Isn't 240Hz one of the standard LCD panel refresh rates?

Problems like this are a pain. Bad electrolytic capacitors are the most common fault I find in LCD monitors and TVs but you already checked those. Are there any other voltages produced by the power supply?
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #5 on: April 25, 2017, 08:28:49 pm »
Isn't 240Hz one of the standard LCD panel refresh rates?

Problems like this are a pain. Bad electrolytic capacitors are the most common fault I find in LCD monitors and TVs but you already checked those. Are there any other voltages produced by the power supply?

The panel has a 60Hz picture so I guess that could be a reference clock being generated by something. The only voltages the power board is putting out are 5V solid, 18.4V solid, and 3.3V square.
 

Offline RGB255_0_0

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #6 on: April 25, 2017, 09:11:20 pm »
Shooting in the dark also. But have you checked it's not the PC and the monitor is actually working fine but getting no signal? Not being condescending.
Your toaster just set fire to an African child over TCP.
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #7 on: April 25, 2017, 10:21:18 pm »
Shooting in the dark also. But have you checked it's not the PC and the monitor is actually working fine but getting no signal? Not being condescending.

Yup - got an identical replacement and it's fine. I'd say I'd use this one to compare voltages and stuff, but the rim isn't easy to remove and I don't really want to mark it  :-\
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #8 on: May 01, 2017, 02:09:09 am »
Quick update - I connected the 5V and on / off pins together on the power board and the backlight on the display came on. I believe this on / off pin is controlled from the logic board. I had the t-con board disconnected at the time but, especially given that the display was in standby when it failed, I'm assuming now that it's most likely to be a logic board problem.

Question is, was it a big chip or a single component? The investigation continues...
 

Offline Rasz

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #9 on: May 01, 2017, 01:33:17 pm »
trace where on / off goes on logic board
check all the dc/dc converters on logic board, there should be 3.3v, probably even 1.5v and maybe 1.2v ones. main chip doesnt run on 5V and needs his own step down
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Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #10 on: May 01, 2017, 11:58:13 pm »
That's easier said than done although it seems to pass through multiple chips (which are working as far as I can tell) before heading into the main heatsinked chips. Might try the heatgun method on that bit - see if it brings it to life. Can't hurt a currently dead board, right?  :-//
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #11 on: May 02, 2017, 12:03:28 am »
Slightly clearer shots of the logic board
 

Online james_s

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #12 on: May 02, 2017, 12:06:43 am »
I hate these kind of faults, it can be very difficult to track down the problem without a schematic. Having access to a working one to swap boards from is a big help to at least narrow down which board the problem is on. Comparison measurements can be useful too, you just have to be careful not to end up with two broken units. Been there, done that.
 

Offline Rasz

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #13 on: May 02, 2017, 04:38:30 pm »
That's easier said than done although it seems to pass through multiple chips (which are working as far as I can tell) before heading into the main heatsinked chips.

start with dc/dc converters on the board, measure voltages on all inductors
check all the fuses ( FBxxx ), there is shit ton of those, I stopped counting at 16

Might try the heatgun method on that bit - see if it brings it to life. Can't hurt a currently dead board, right?  :-//

ah yes, the please bro retard method of destroying fixable electronics
Who logs in to gdm? Not I, said the duck.
My fireplace is on fire, but in all the wrong places.
 
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Online james_s

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #14 on: May 02, 2017, 05:46:56 pm »
A hair dryer and freeze spray can be effective tools to track down intermittent faults but I would avoid a heat gun, they get too hot. In this case it doesn't sound like the fault is intermittent so there's probably little point in heating and cooling parts.
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #15 on: May 06, 2017, 03:01:53 pm »
check all the fuses ( FBxxx ), there is shit ton of those, I stopped counting at 16

There's loads of them all over the place, but I'm fairly sure they're just ferrite beads.
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #16 on: May 06, 2017, 03:04:52 pm »
A hair dryer and freeze spray can be effective tools to track down intermittent faults but I would avoid a heat gun, they get too hot. In this case it doesn't sound like the fault is intermittent so there's probably little point in heating and cooling parts.

You might be right, although I've tested pretty much every component now and everything is working as expected (I've found a whole range of voltages and clocks on the board). There's a few chips here and there that I haven't found datasheets for, but it feels a lot like one of the logic chip has died to me. ASUS don't sell individual parts and there aren't currently any dead screens on eBay to dissect, so I think I need to leave this for now!
 

Offline Rasz

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #17 on: May 06, 2017, 08:36:54 pm »
check all the fuses ( FBxxx ), there is shit ton of those, I stopped counting at 16

There's loads of them all over the place, but I'm fairly sure they're just ferrite beads.

hah you are right, looks like they had some trouble with EMI
Who logs in to gdm? Not I, said the duck.
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Online james_s

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #18 on: May 08, 2017, 05:58:31 pm »
Set up a saved search on ebay for that model monitor and "for parts or repair" status, that way you'll automatically get an email if one comes up. Also post in the wanted section on this and any similar forums you belong to, and if you have a thing like craigslist, sooner or later you might find an identical monitor with a cracked panel. It's fairly common for LCD TVs to get cracked by kids horsing around or idiots with anger management problems, probably happens to monitors too.
 

Offline sdomenic

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #19 on: May 30, 2017, 02:13:31 pm »
Not related to your problem but I'm also interested in opening my PB287Q due to intermittent on/off of the LCD. I suspect something loose, since I'm able to smack into the on state. Can you share what method you used to open the unit? Since I don't see an obvious entry point.
 

Offline wraper

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #20 on: May 30, 2017, 02:23:33 pm »
The last wire is orange, labelled DIM, and gives a square wave 240Hz between 3.3V and 120mV. I haven't found a specsheet for the board (and ASUS won't help) so I'm not sure if this is right. Unless someone can tell me if this is right or wrong I'll try to work the circuit back and figure it out, eventually! The one thing I will say is that 240Hz isn't a natural multiple of anything - my household supply is 240V @ 50Hz, so 240Hz is being generated by something other than the mains...
Sounds like backlight brightness pwm control.
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #21 on: May 30, 2017, 02:57:51 pm »
Not related to your problem but I'm also interested in opening my PB287Q due to intermittent on/off of the LCD. I suspect something loose, since I'm able to smack into the on state. Can you share what method you used to open the unit? Since I don't see an obvious entry point.

Looking at the LCD panel, the first ridge at the front is where you need to get your tool in. I used a craft knife (all I had to hand) because the gap is so tiny that it's not obvious. Once you have something to grip it pulls apart like any other LCD screen. I needed to jimmy mine around the edge a bit - you will probably end up marking it in some places.
 

Offline EHT

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #22 on: May 30, 2017, 11:32:34 pm »
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?

I suggest rather than shorting it, cut the wire linking ON/OFF between the logic & PSU boards, then attach a 1k resistor from +5V to ON/OFF on the PSU side.

With ON/OFF connected again, you could try different input ports on the monitor to see if none of them make the logic board turn the backlight on.

You may be aware but be very careful testing the circuit as it has lethal 400V DC in the PSU and half of the PSU board is non-isolated (live). This is even the case when it is in standby. Luckily looks like your problem is not in the live circuit. Best keep the PSU PCB mounted in the chassis if at all possible.
« Last Edit: May 30, 2017, 11:34:14 pm by EHT »
 

Offline wizpip

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #23 on: May 31, 2017, 12:45:42 am »
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.
 

Offline stj

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Re: Duff 28" ASUS PB287Q 4K monitor
« Reply #24 on: May 31, 2017, 01:04:40 am »
how old is it?
ASUS usually has a long warranty - 3years or more
 


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