[SOLVED] GPU and CPU power

[bnzSup]

So... the other day I was helping my Father in law build a pc for my girlfriends brother and we built everything, but when it was time to power it on everthing lighted up, the fans, the CPU cooler, except the GPU. So we removed the GPU and tried placing it again, didn't work. After that, we forgot the 12V CPU power cable disconnected and turned on the pc, and for some reason the GPU turned on.
So what we know is:
When the CPU 12V cable is connected, the GPU doesn't turn on, but if you disconnect it (the 12V cpu cable), the GPU turns on.
Here is the parts list:
https://de.pcpartpicker.com/list/2nZ9F8
The CPU and GPU are used.

 

[Krotow]

Look like mismatched PSU cables - CPU 12V cable mismatched with PCIe 12V cable.

Also GPU will not work as expected without 12V cable, so connect it back. Still curious why it turned in without 12V cable at all. But it would brownout when starting a game with subsequent computer restart anyway.

 

[bnzSup]

Look like mismatched PSU cables - CPU 12V cable mismatched with PCIe 12V cable.

Also GPU will not work as expected without 12V cable, so connect it back. Still curious why it turned in without 12V cable at all. But it would brownout when starting a game with subsequent computer restart anyway.

The cables aren't mismatched, they are labeled CPU and PCIe, so I'm sure they are in the right place. We don't get video because while the CPU has power, the GPU doesn't (and the Ryzen 1700 doesn't have an IGPU) so we cannot get to the BIOS.

 

[Krotow]

That system still can't work properly when 12V cables are disconnected. At least CPU, GPU, PSU and motherboard match by specification. If all cables are connected properly, all must work. If not, check BIOS POST beeps/LEDs on motherboard. Also particular GPU and monitor may not work together well on low screen resolutions. I had this issue with my nephew computer (ASRock B550M Pro4 motherboard) and decade old 1366x768 monitor which had no BIOS screen picture at all when turned on. Turned out it was monitor on low screen resolution which again worked just fine in his native 1366x768 in Windows.

 

[Unolocogringo]

Give it some time.
When I first built my new Ryzen system I thought I had bad hardware.
Pulled it out of my desk and rechecked everything. ALL good.
Put it back in desk and hit power button.
Received a call that distracted me for about a minute and a half.
Was about to kill power and pull it again when I heard the glorious single BEEP and monitor turned on.
Searched around and found other people had the same experience.

 

[Krotow]

Give it some time.
...
Was about to kill power and pull it again when I heard the glorious single BEEP and monitor turned on.

Sure, already forgot about it. POST procedure at first time on AM4 boards is quite long. Mine boards at least have POST status LEDs - seen how BIOS is struggling to get all kinks together for like a minute. Subsequent POST-ing was already much faster.

 

[bnzSup]

That system still can't work properly when 12V cables are disconnected. At least CPU, GPU, PSU and motherboard match by specification. If all cables are connected properly, all must work. If not, check BIOS POST beeps/LEDs on motherboard. Also particular GPU and monitor may not work together well on low screen resolutions. I had this issue with my nephew computer (ASRock B550M Pro4 motherboard) and decade old 1366x768 monitor which had no BIOS screen picture at all when turned on. Turned out it was monitor on low screen resolution which again worked just fine in his native 1366x768 in Windows.

Tought about that to, but the monitor is 1920x1080, so no luck there.

 

[bnzSup]

Give it some time.
When I first built my new Ryzen system I thought I had bad hardware.
Pulled it out of my desk and rechecked everything. ALL good.
Put it back in desk and hit power button.
Received a call that distracted me for about a minute and a half.
Was about to kill power and pull it again when I heard the glorious single BEEP and monitor turned on.
Searched around and found other people had the same experience.

Man, totally forgot about this, is the first time this MoBo is posting, I'll try and do this.

 

[bnzSup]

Give it some time.
When I first built my new Ryzen system I thought I had bad hardware.
Pulled it out of my desk and rechecked everything. ALL good.
Put it back in desk and hit power button.
Received a call that distracted me for about a minute and a half.
Was about to kill power and pull it again when I heard the glorious single BEEP and monitor turned on.
Searched around and found other people had the same experience.

No luck here either, the system didn't post even after 3 minutes, the GPU doesn't turn on while the cpu is connected.

 

[Krotow]

Another thing about first time boot that may interest you. Remembered about issues in my recent new machine with B550 MOBO (details in signature). On first turning on same picture as you have. Black screen, no signal and MOBO POST indicator stuck on VGA. On more detailed inspection realized that I may be caused by PCIe VGA cable in wrong PSU socket. My PSU have 4 managed PCIe 12V sockets and does not turn on 12V if PCIe 1 and PCIe 2 sockets are vacant. I connected GPU to PCIe 3 socket. Silly me. Reconnected to PCIe 1 (also replaced CPU 12V cable from 4+4-pin to 8-pin cable (better match to my MOBO). After that POST got past VGA into BIOS. Next surprise was missing both NVMe drives and non-working RAM XMP profiles. Anything above 2133 MHz did stuck on black screen with POST status RAM LED lit. Though it was possible to get back into BIOS after CMOS clearing by jumper on MOBO. This was a moment of little horror for me. All this hardware did cost me a price of good used car. Luckily had a laptop nearby. Downloaded latest BIOS for my MOBO to USB stick, flashed it though BIOS and after reboot all things instantly started to work. Including RAM overclocking to 4200 CL16. Why I'm telling this? I believe you should recheck cable connections once more. Don't hesitate to look into manuals Then if you still are on black screen, reset CMOS - connect both pins in "CLRCMOS1 " connector at MOBO back side near case audio cable connector for 3-5 seconds. You can use flat screwdriver for that too, but don't short something else on board.