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A couple of days ago I bought two new monitors (iiyama g-master GB2730HSU-B1), and by doing so I also switched to using display port instead of HDMI (EVGA GTX 970 graphics card).

Now a weird issue has started happening. Whenever I power down the system, a couple of LED's on my motherboard and case will stay on, and my CPU fan and front case fan will keep spinning (though at low speed).

Initially I thought this may have been some residual power, so I waited 5 minutes, but it wouldn't power down. Thinking my PSU may be defecting and leaking some power I unplugged it from the grid/mains. This didn't power down the motherboard either.

After a process of elimination I found out that when I unplug both my display port cables it will power down completely, unplugging a single one doesn't power it down either. Replugging the cables won't power up the motherboard again.

Simply turning off the monitors doesn't work either, though unplugging them from the grid/mains does work.

I am using a MSI b150 gaming m3 motherboard. Operating system is Windows 10 64bit.

I have tried enabling the EuP setting in the "Advanced > Power settings" in the bios. Which yielded no results.

  • Are you on Windows? If yes, then does this happen when booting in Safe mode? – harrymc Jul 10 '19 at 8:32
  • @harrymc Yes I am running windows 10 (updated question to reflect this). I have not tried booting it in safe mode and cannot try this right away. Will try this as soon as i'm home. – Remy Jul 10 '19 at 8:38
  • If this doesn't happen in Safe mode, then some installed third-party application or driver is the cause, and I will answer with a tool+procedure for finding it out. – harrymc Jul 10 '19 at 8:41
  • @harrymc Unfortunately the issue persists, even after having booted windows in safe-mode with network and everything disabled. – Remy Jul 10 '19 at 15:27
  • Not yet conclusive as safe-mode with network loads the network driver. Could you try booting in simply safe-mode? – harrymc Jul 10 '19 at 15:37
4
+100

This is likely happening due to the monitors supplying a small amount of power over the display cable. The giveaway is this bit:

Thinking my PSU may be defecting and leaking some power I unplugged it from the grid/mains. This didn't power down the motherboard either.

There is only one potential solution to this that I can some up with: find a display cable that doesn't have wires for the power lanes, or modify one yourself. It shouldn't be too hard, but you have to be very careful not to damage the other connections. This pinout might help.

Display Port Pinout

+---------+--------------+---------------------+---------------+-------------------+
|  Pin    | Transmitting End                   | Receiving End                     |
+         +--------------+---------------------+---------------+-------------------+
| Number  | Pin Name     | Description         | Pin Name      | Description       |
+---------+--------------+---------------------+---------------+-------------------+
|       1 | ML_Lane 0+   | Lane 0 (positive)   | ML_Lane 3-    | Lane 3 (negative) |
|       2 | GND          | Ground                                                  |
|       3 | ML_Lane 0-   | Lane 0 (negative)   | ML_Lane 3+    | Lane 3 (positive) |
|       4 | ML_Lane 1+   | Lane 1 (positive)   | ML_Lane 2-    | Lane 2 (negative) |
|       5 | GND          | Ground                                                  |
|       6 | ML_Lane 1-   | Lane 1 (negative)   | ML_Lane 2+    | Lane 2 (positive) |
|       7 | ML_Lane 2+   | Lane 2 (positive)   | ML_Lane 1-    | Lane 1 (negative) |
|       8 | GND          | Ground                                                  |
|       9 | ML_Lane 2-   | Lane 2 (negative)   | ML_Lane 1+    | Lane 1 (positive) |
|      10 | ML_Lane 3+   | Lane 3 (positive)   | ML_Lane 0-    | Lane 0 (negative) |
|      11 | GND          | Ground                                                  |
|      12 | ML_Lane 3-   | Lane 3 (negative)   | ML_Lane 0+    | Lane 0 (positive) |
|      13 | CONFIG1      | connect to ground (can be direct or via a pulldown)     |
|      14 | CONFIG2      | connect to ground (can be direct or via a pulldown)     |
|      15 | AUX CH+      | Auxiliary Channel (positive)                            |
|      16 | GND          | Ground                                                  |
|      17 | AUX CH-      | Auxiliary Channel (negative)                            |
|      18 | Hot Plug     | Hot Plug detect                                         |
|      19 | Return       | Return (for power)                                      |
|      20 | DP_PWR       | Power for connector (3.3 V 500 mA)                      |
+---------+--------------+---------------------+---------------+-------------------+
| improve this answer | |
  • I just looked at the specs of the DP cables i bought and it indeed says "power 20 pin connected", and reading up on this there are complaints of it indeed providing power back to the GPU, potentially damaging it. I'm gonna get some new ones without this which will most likely solve it. (I cant upvote your great answer because i got sub 15 points due to bounty unfortunately, which will come your way if it is resolved!) – Remy Jul 10 '19 at 15:33
  • @remy_rm good luck! – undo Jul 10 '19 at 15:34
  • Swapped the DP cables for non pin 20 ones, and it resolved it, thanks for the insight! – Remy Jul 11 '19 at 11:06
  • @remy_rm yay :) – undo Jul 11 '19 at 15:11

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