Duff 28" ASUS PB287Q 4K monitor - Page 1
Forum section: electronics / repair

author: wizpip
author_rank: Contributor
timestamp: April 24, 2017, 01:17:52 am
content: 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-P01-001-003ELogic board: 715G6681-M02-000-005IT-con board: InnoLux V390DK1-CLS1Any insight you can give me on what to test or do next would be much appreciated!

author: Rasz
author_rank: Super Contributor
timestamp: April 25, 2017, 12:46:43 am
content: shooting in the dark - whats on the brown wire? maybe its power good and its not good keeping controller board in permanent reset?

author: wizpip
author_rank: Contributor
timestamp: April 25, 2017, 05:45:15 pm
content: Quote from: Rasz on April 25, 2017, 12:46:43 amLabelled as On/Off and has a constant (slightly noisy) 72mV...

author: wizpip
author_rank: Contributor
timestamp: April 25, 2017, 06:56:49 pm
content: 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...

author: james_s
author_rank: Super Contributor
timestamp: April 25, 2017, 07:37:01 pm
content: 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?

author: wizpip
author_rank: Contributor
timestamp: April 25, 2017, 08:28:49 pm
content: Quote from: james_s on April 25, 2017, 07:37:01 pmThe 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.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: April 25, 2017, 09:11:20 pm
content: 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.

author: wizpip
author_rank: Contributor
timestamp: April 25, 2017, 10:21:18 pm
content: Quote from: RGB255_0_0 on April 25, 2017, 09:11:20 pmYup - 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

author: wizpip
author_rank: Contributor
timestamp: May 01, 2017, 02:09:09 am
content: 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...

author: Rasz
author_rank: Super Contributor
timestamp: May 01, 2017, 01:33:17 pm
content: trace where on / off goes on logic boardcheck 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

author: wizpip
author_rank: Contributor
timestamp: May 01, 2017, 11:58:13 pm
content: 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?

author: wizpip
author_rank: Contributor
timestamp: May 02, 2017, 12:03:28 am
content: Slightly clearer shots of the logic board

author: james_s
author_rank: Super Contributor
timestamp: May 02, 2017, 12:06:43 am
content: 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.

author: Rasz
author_rank: Super Contributor
timestamp: May 02, 2017, 04:38:30 pm
content: Quote from: wizpip on May 01, 2017, 11:58:13 pmstart with dc/dc converters on the board, measure voltages on all inductorscheck all the fuses ( FBxxx ), there is shit ton of those, I stopped counting at 16Quote from: wizpip on May 01, 2017, 11:58:13 pmah yes, the please bro retard method of destroying fixable electronics

author: james_s
author_rank: Super Contributor
timestamp: May 02, 2017, 05:46:56 pm
content: 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.

author: wizpip
author_rank: Contributor
timestamp: May 06, 2017, 03:01:53 pm
content: Quote from: Rasz on May 02, 2017, 04:38:30 pmThere's loads of them all over the place, but I'm fairly sure they're just ferrite beads.

author: wizpip
author_rank: Contributor
timestamp: May 06, 2017, 03:04:52 pm
content: Quote from: james_s on May 02, 2017, 05:46:56 pmYou 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!

author: Rasz
author_rank: Super Contributor
timestamp: May 06, 2017, 08:36:54 pm
content: Quote from: wizpip on May 06, 2017, 03:01:53 pmhah you are right, looks like they had some trouble with EMI

author: james_s
author_rank: Super Contributor
timestamp: May 08, 2017, 05:58:31 pm
content: 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.

author: sdomenic
author_rank: Newbie
timestamp: May 30, 2017, 02:13:31 pm
content: 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.

author: wraper
author_rank: Unknown
timestamp: May 30, 2017, 02:23:33 pm
content: Quote from: wizpip on April 25, 2017, 06:56:49 pmSounds like backlight brightness pwm control.

author: wizpip
author_rank: Contributor
timestamp: May 30, 2017, 02:57:51 pm
content: Quote from: sdomenic on May 30, 2017, 02:13:31 pmLooking 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.

author: EHT
author_rank: Frequent Contributor
timestamp: May 30, 2017, 11:32:34 pm
content: 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.

author: wizpip
author_rank: Contributor
timestamp: May 31, 2017, 12:45:42 am
content: Quote from: EHT on May 30, 2017, 11:32:34 pmNope, there's no response from the panel at all.

author: stj
author_rank: Super Contributor
timestamp: May 31, 2017, 01:04:40 am
content: how old is it?ASUS usually has a long warranty - 3years or more

author: wizpip
author_rank: Contributor
timestamp: May 31, 2017, 01:42:45 am
content: Quote from: stj on May 31, 2017, 01:04:40 amWell, 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!

author: stj
author_rank: Super Contributor
timestamp: May 31, 2017, 02:02:52 am
content: 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.

author: EHT
author_rank: Frequent Contributor
timestamp: May 31, 2017, 09:21:49 am
content: Quote from: wizpip on May 31, 2017, 12:45:42 amOK, 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.

author: wizpip
author_rank: Contributor
timestamp: May 31, 2017, 03:05:54 pm
content: Quote from: EHT on May 31, 2017, 09:21:49 amI'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.

author: stj
author_rank: Super Contributor
timestamp: May 31, 2017, 04:29:55 pm
content: 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 !!

author: wizpip
author_rank: Contributor
timestamp: May 31, 2017, 05:52:59 pm
content: Quote from: stj on May 31, 2017, 04:29:55 pmThat's probably my fault - I desoldered a lot of things to test them! Didn't do a particularly good job putting it back together...

author: stj
author_rank: Super Contributor
timestamp: May 31, 2017, 05:54:26 pm
content: no stress cracks, faint rings on some of the factory joints.

author: EHT
author_rank: Frequent Contributor
timestamp: May 31, 2017, 08:45:36 pm
content: 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).

author: cirthix
author_rank: Contributor
timestamp: June 10, 2017, 10:00:45 pm
content: 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?

author: wizpip
author_rank: Contributor
timestamp: June 10, 2017, 10:24:49 pm
content: Quote from: cirthix on June 10, 2017, 10:00:45 pmNo - 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 39.6Quote from: cirthix on June 10, 2017, 10:00:45 pmFor 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.Quote from: cirthix on June 10, 2017, 10:00:45 pmMain board - the logic board? Any idea which one it'd be from the pic?Quote from: cirthix on June 10, 2017, 10:00:45 pmNo - 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.

author: cirthix
author_rank: Contributor
timestamp: July 12, 2017, 12:40:18 am
content: In that case, check this 12v regulator

author: GraXXoR
author_rank: Contributor
timestamp: February 20, 2024, 02:49:52 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: February 20, 2024, 03:17:53 pm
content: 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.