When CPU is powered, computer will not power on properly.

[irobertsonbrown]

So I'm having an issue that I believe to be either related to my CPU or motherboard (AMD Ryzen 7 1700x and ASUS X370-pro AM4). When I power on the system everything works fine, all the fans on the case, GPU, and CPU fan all work properly for a few seconds and then turn off. I never get any display on monitor. When I unplug the CPU from the Power supply though, the computer stays on, with motherboard lights turning on, all fans spinning. Removing the GPU, Wifi Card, RAM, Sata connections, etc. have made no difference, the only change that has resulted in any difference is whether or not the CPU is powered. This has been tested with two power supplies, both yielding the exact same results. I'm assuming this means there is an issue with either the Motherboard or the CPU, I have tried removing and putting back the CPU and replacing the thermal paste on the CPU to no avail. I don't have access to another AM4 chip to test in my motherboard, is there some other way to determine where the issue is coming from?

Thanks

CPU: AMD Ryzen 1700x
Mobo: ASUS X370-pro ATX AM4
CPU FAN: Noctua NH-D15 SE-AM4
PSU: CSM 750W 80+ Modular ATX Power supply
RAM: Corsair - Vengeance LPX 16GB DDR4-3000
GPU: GTX 980 4GB - Windforce
CASE: Phanteks - Enthoo pro ATX full tower

 

[kerberos_20]

by removing cpu from psu u mean that 8pin eps cable?

 

[irobertsonbrown]

by removing cpu from psu u mean that 8pin eps cable?

Yes, when the 8pin connector is unplugged everything will turn on properly.

 

[kerberos_20]

Well, the problem is that the system won't boot without the auxiliary CPU power feed connected, so you can't really say that is the cause. Even if you had perfect hardware, and you disconnected that plug, the system would fail to boot.

At this point though, if you've replaced the PSU, and the problem persists, the most likely cause would be a defective motherboard. I'd suggest googling bad caps and then inspecting your system, because this is a fairly typical symptom of that. It is also frequently caused by a bad PSU.

 

[finitekosmos]

by removing cpu from psu u mean that 8pin eps cable?

Yes, when the 8pin connector is unplugged everything will turn on properly.

Are you using the correct cable for EPS power? I ask because it is possible to plug an 8 pin PCIe power cable into the EPS socket despite the fact the cables are keyed differently.

 

[irobertsonbrown]

Well, the problem is that the system won't boot without the auxiliary CPU power feed connected, so you can't really say that is the cause. Even if you had perfect hardware, and you disconnected that plug, the system would fail to boot.

At this point though, if you've replaced the PSU, and the problem persists, the most likely cause would be a defective motherboard. I'd suggest googling bad caps and then inspecting your system, because this is a fairly typical symptom of that. It is also frequently caused by a bad PSU.

I have checked for visible signs of damage on the motherboard and found none, It's also worth noting that both the CPU and motherboard have been in the system for about a year and this is the first time I've had issues. Are there ways beyond inspecting for bad caps to test my motherboard? From what I've gathered by looking at forum posts it seems the issue could be caused by either a faulty motherboard or CPU, is it more likely that the issue is with motherboard? Once again, everything works perfectly UNTIL I connect the CPU power feed at which point the system won't remain on.

 

[irobertsonbrown]

by removing cpu from psu u mean that 8pin eps cable?

Yes, when the 8pin connector is unplugged everything will turn on properly.

Are you using the correct cable for EPS power? I ask because it is possible to plug an 8 pin PCIe power cable into the EPS socket despite the fact the cables are keyed differently.

Yes I am sure, the EPS power cable is labeled CPU, and has been powering it fine for a year now.

 

[finitekosmos]

Great! There is in that case a chance that you may have an issue with your PSU, is there any way you could test your system with a different PSU of the same wattage? This would definitely tell you where the problem lies, if it works your PSU is the problem, if it doesn't then something is shorting on your mobo.

I don't think there is much else we could recommend trying I'm afraid!

 

[irobertsonbrown]

Great! There is in that case a chance that you may have an issue with your PSU, is there any way you could test your system with a different PSU of the same wattage? This would definitely tell you where the problem lies, if it works your PSU is the problem, if it doesn't then something is shorting on your mobo.

I don't think there is much else we could recommend trying I'm afraid!

Yes, I tested with another power supply (The wattage was different but I had the same results when trying to start it up.), Unfortunately that build doesn't have an AM4 chip or compatible motherboard that I could use for testing. Would you recommend replacing motherboard as next step?

 

[kerberos_20]

replacing mobo would be your next step

 

[irobertsonbrown]

replacing mobo would be your next step

Alright, I'll look into that next. Thanks for responses!