Question Dead System - Does it matter Which Part of split 8 Pin Power?

4dlfisher

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Nov 27, 2008
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I am working with a Gigabit Z390 Designair MOBO (i9 9900K CPU/ Nocturna NH-U12A cooler). Working through problems where it won't Boot/give graphics. This is not my 1st build and it was working until recently.

I have seen the "No POST", "system won't boot", and "no video output" troubleshooting checklist. Working through steps there to double check all my debugs. Looking at the Power config in step #2.

I have an 8 pin power AND a 4 pin on this MOBO. The Cooler Master MWE v2 750 Gold+ PSU cord splits one of the Power feeds into 2 blocks of 4 - does it matter which 4 pin block is used for the 4 pin feed on the board? and if so, how do you tell? (all 8 got to PSU, so I thought it wouldn't matter?)

FYI - This started with dead Seasonic Focus+ PSU. I have been using this build steady for ~5 mo. I did a routine powered down of the unit in Windows over the holidays, and it was cold for ~2 days, and then never would (re)start (got single click, lights on MOBO and some cards, but no case or CPU fans and no boot - Brief flash on 1 LED on MOBO and nothing else...). I recently replaced the PSU, assuming it is the most likely culprit, and now get power/lights on internal components, all fans running (except GPU - which prior to shut don had been tuned to run fans starting at 35C since the unit always seemed to run hot), and behavior like an apparent boot, but no Video?!

I have LED indicators on MOBO and it hangs at VGA (steady red) (no Mobo speaker).

I have removed the Sapphire Radeon RX 5600 XT 6 GB PULSE Video Card in hopes I might get integrated video from MOBO, but still nothing.

Also tried different monitor, just to make sure... ?!
(Note - my graphics card only has HDMI/DP outputs, and the MOBO is the same - saw comments about may need to use DVI/VGA port in diagnostics, but don't have that option - the only bench monitor I have is DVI/VGA, and I am using HDMI adapter cord to it, but I have tried this on newer HDMI based monitor also & no change)

Boot LEDs have never hung at the RAM stage, so I have not done the step to pull all the RAM (that may be my next step). I am using 4 sticks of OLOy 16 GB DDR4-3600 CL18 Memory

I also have not done the bread boarding step (yet), since that means tearing down what was a working system just 2 weeks ago

ANY debug suggestions are welcome - have an expensive desk ornament and I am really stuck :-(
 

faalin

Judicious
You need the 8 plus 4 pin plugged in for the motherboard, most PSU will label this CPU or ESP on the cables.

Your PSU has a 24 pin
1 4+4 esp plug
1 8 pin esp

Plug the 8 pin in and then split and use one of the 4+4 pins in.
 
Last edited:

4dlfisher

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Nov 27, 2008
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You need the 8 plus 4 pin plugged in for the motherboard, most PSU will label this CPU or ESP on the cables.

Your PSU has a 24 pin
1 4+4 esp plug
1 8 pin esp

Plug the 8 pin in and then split and use one of the 4+4 pins in.
Sorry if I was not clear: I have the 8 Pin plugged. I also have a 4 pin add (next to it) plugged in from a split block connector. I want to know if a specific side/ segment of the split block needs to be connected to the 4 pin segment, and if so, how do you know which side?
 

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