Z820 Workstation - blue power light for 15 seconds, then off for 3 and tries again, no post or beeps

[cm_dalton]

Our user was working on his Z820 Workstation (LJ452AV) when it just cut out on him.

Now it powers on with a solid blue power light, sits for about 15 seconds, then turns off for 3 seconds, and stays in this loop.

If I pull power completely, the fans make a brief pulse when the system is powered up, but then it is quiet for 15 seconds and resumes the loop.

The system does not post, the LED on the motherboard stays blue, so it appears the RAM is okay.

I've pulled and reseated the graphics card...

Other posts suggest their fans run full tilt without posting, but this one is ghostly silent except for a brief click when it powers up again and the gentle whir of the NVIDIA card's fan.  The fans in the CPU chamber only start briefly on the first power up after removing the power cable for a time...

I gather it's likely the motherboard or the power supply, but I'm trying to make sure before getting too invasive and throwing good money after bad...

[DGroves]

please read the z820 "service manual" that hp makes available on their website

in the manual there is a section on how to perform a test of the power supply supply (BST Test) along with other basic tests you can perform

https://support.hp.com/us-en/product/hp-z820-workstation/5225041/manuals

if the power supply tests good then you might have a corrupted bios (unlikely based on your description) you can try a crysis recovery of the bios (search this forum for posts on this by "SDH")

[cm_dalton]

Thank you for the information about the power supply self-test.  I had the service manual up, but didn't catch the BIST feature of the power supply.  It tests fine, so now I know I need to move on to the more invasive steps.  I'll keep looking, but it feels like it's going to be the motherboard and not just a BIOS issue...