Question System not POSTing sometimes unless I connect display via HDMI first rather than Displayport

Jan 4, 2021
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All,

MOBO - MSI B450 Tomahawk
CPU - Ryzen 5 2600
RAM - G.Skill Aegis 16 GB (2 x 8 GB) DDR4-3000
GPU - XFX AMD RX 580

I had been connecting my monitor through a Displayport off the GPU. One day about a month ago, my machine would not post. It had never happened before. I didn't know about the EZDebug LED at this point so not sure what it was showing. For whatever reason, probably because I just switched to a new monitor and started using Displayport, I switched back to an HDMI cable and machine booted. This cat and mouse happened for a few days. Sometimes it would post no issues and sometimes not. I noticed that it seemed like once the machine was "warmed up", it wouldn't have problems POSTing but if i had turned it off overnight and let it cool off, the next time the boot happens, it would not POST. Then I decided to downgrade my BIOS and the issue went away for a couple of weeks. I thought I was in the clear until tonight when it wouldn't POST again. I checked out the EZDebug LED and it would flash CPU and then stay red on DRAM. Fans are spinning, drives are running but I would retry about 10 times. I even took out the 2 sticks of RAM and tried to debug one at a time. Nothing worked. Then I remembered the HDMI trick so I disconnected the Displayport cable and connected an HDMI cable from the GPU to the monitor and it booted. Then i switched back to the DP cable and it's working again. I cannot think of why this could be happening other than a bad MOBO. If anyone can think of any other ideas, please advise.

If it happens again tomorrow, I'm planning to swap out the 2 pcs of RAM with another 2 from another almost identical machine I also built. I want to rule out the RAM first.

Thanks in advance.
 

jojesa

Illustrious
Is the computer not booting at all when the DP is connected or it is booting but there isn't any display?
Does it happens if you connect the DP cable to any DP port on the GPU?
Does it happens if your monitor it set to the DP input instead of auto input?
Since you are connecting the DP and HDMI cables to the GPU, then it might not be at all related to the motherboard or the RAM.
 
Jan 4, 2021
3
0
10
0
Is the computer not booting at all when the DP is connected or it is booting but there isn't any display?
Does it happens if you connect the DP cable to any DP port on the GPU?
Does it happens if your monitor it set to the DP input instead of auto input?
Since you are connecting the DP and HDMI cables to the GPU, then it might not be at all related to the motherboard or the RAM.
Thanks.
1) When the DP is connected, I don't believe it's going through the boot sequence at all because I don't see the HD lights and there's no signal to the monitor. It appears to sit at the EZDEBUG DRAM (red LED) and doesn't move onto the VGA followed by boot LEDs. And the monitor says no signal.

2) Good thought. I'm forgetting whether I've tried the other 2 DP ports as it was about 3 weeks ago now but I think I did. I'm pretty sure it'll happen again so I'll try that before swapping out the memory.

3) Yes, when this happens, I take the monitor out of Auto and set it explicitly to the DP input. Otherwise, it auto switches it back to my laptop which has a signal. That's how I know it's saying no signal.

4) I'm going to try to eliminate the RAM first. However, I can't think of how an HDMI signal from the GPU could possibly affect the POST tests. At least not that early in the test I would've thought.
 

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