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Old 05-21-2019, 12:31 PM   #1
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Default ASUS PG279Q dead panel

I'm currently working on a ASUS PG279Q (27", 2560x1440 IPS G-Sync, pretty expensive when new) which shows no image. According to the owner it worked fine one evening and didn't work the next day. No prior change in device behavior, apart from two stuck pixels which have been there since the beginning.

Things I checked so far:

- The backlight is fully operational
- When turned on, the backlight comes on, and the image remains dark. If you look very closely about 2/3 of the panel are fully black while 1/3 are slightly brighter. Some very faint vertical stripes as well. (See attached IMG_....)
- Power supply, external 19 V brick is ok
- Internal power supplies; the main logic board is a bit sparse when it comes to labelling things, but I found the converters for 5 V and 3.3 V, clean output

My conclusion so far: Main power seems to be ok.

- LVDS clocks coming from the rescaler FPGA to the panel controller board, they are all clean, nice ~50 MHz clocks.
- While I don't have the necessary equipment (due to the high bandwidth) I can see, when supplied with a signal, that there are signals on the LVDS lanes themselves as well.
- There is a CLK_OK test point on the panel controller board (AOU part), which is HIGH (3.3 V)
- There is a SYNC test point on the panel controller board, which shows a clean 60 Hz square wave

My conclusion so far: LVDS output from the rescaler FPGA is probably ok.

- There are various test points for supply voltages on the panel controller board, which all look clean (AC wise) and have plausible values: 12 V, 3.3 V, 1.3ish V, -7 V.
- There is no visible damage to the case, panel etc. at all
- No visible damage on the flexprint-to-controller board bond
- There are two identical controller ICs on the controller board. There are a bunch of duplicate test points each marked ..._T1 and ..._T2. From how the differential signal traces are routed it seems the panel is internally split into two halves.

My conclusion so far: ??? Either the entire panel failed at exactly the same time, or there must be something wrong on the controller board. I think a missing / failed bias voltage used by the panel driver ICs might be a plausible explanation?

Very rarely when left powered on with an input signal the panel shows vertical, colored bands. It doesn't always do this, just sometimes. See attached image (DSC_...). (This might be unrelated to having an input signal and just might be due to running for some time: it will always go into standby after a little while with no signal present).


The panel is a M270DAN02.3 made by AUO. The control board also has this marking on it: 27M12-C0A.

The two controller chips on the panel control board are AUO-12409 (TQFP-128). In the DC/DC converter section of the control board are an extra two AUO-labelled chips: AUO P302-11 (QFN-40), AUO S301A21 (QFN-32). There's also an RT8293BL DC/DC controller chip on there. I also checked the inductors for continuity and the flyback diodes for forward voltage, they all seem OK from those cursory tests.

The panel controller is connected via four cables to the logic board, each of those cables carries two LVDS links with four data pairs and one clock pair (for a total of 8 LVDS links with 32 lanes total). Each of the controller chips is connected to half of those.

I can post hi-res pics of the panel board if someone can make use of it.
Attached Images
File Type: jpg DSC_2751.JPG (29.3 KB, 6 views)
File Type: jpg IMG_1710.jpg (53.2 KB, 4 views)

Last edited by dom0; 05-21-2019 at 12:58 PM..
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