HP Z420 4 Beep on boot, red light flashing BUT works if CMOS taken out and put back in after 30 mins

[zabits]

Hi there,

My workstation is dual boot MacOS and Ubuntu. I'm having problems booting it up. It beeps 4 times, once per second, pause for 2 seconds and repeat.

I can make it boot if I remove CMOS battery and put it back in after at least 30 mins but this is temporary as if the workstation restarts then the same problem persists.

BIOS settings need to be ACHI in order for MacOS to function but since I take out the CMOS battery the bios resets to default which is RAID+ACHI. If I change the BIOS then the workstation restarts and same problem persists.

I have reseated the RAM and other peripherals but the problem still persists.

Do you think theres a problem with my PSU or motherboard?

[mdklassen]

From: https://support.hp.com/us-en/document/c02222922 

if you have an AMI BIOS:

Beeps: 4, 5, 6, 7

Fatal errors related to the operation of critical motherboard components - such as the CPU.

Ouch!

[zabits]

Hi mdklassen,

I found out that my BIOS is AMI. I took out CMOS battery and let the desktop on its side unplugged without battery for 24 hours. I put the CMOS battery back and plugged in my usb to update the bios. However I couldn't get it to boot from my usb but I was able to boot into my Ubuntu.

Once in Ubuntu I restarted my computer and changed the bios to that my MacOS would work. Now my computer is back to normal. I'm still not sure why my computer was acting up. I report how my computer works once its shut down and turned on again tomorrow.

[zabits]

I unplugged the desktop from the mains and left it overnight. In the morning I took out the CMOS jumper and I put it back 2-3 hours later.

I put the CMOS jumper back in and plugged in my usb and connect desktop to mains. The desktop booted up without problems. Do you think there is still problem with my CPU?

[zabits]

I think the problem might be with my PSU. I noticed that I can boot into my PC without problems with the cord is unplugged for at least couple of hours. Perhaps its taking long time for the energy to discharge?

I hope I can figure out the long term solution and appreciate any help that I can get.

[mdklassen]

>  I noticed that I can boot into my PC without problems [when] the cord is unplugged for at least couple of hours.

> Perhaps it's taking long time for the energy to discharge?

Perhaps, turn the computer off, for a few hours, WITHOUT unplugging the cord.

Then, if it starts normally, then unplugging the cord makes no difference.

Perhaps, the motherboard is "dying" -- when it is "warm", and you try to restart, it has an intermittent problem.

When the motherboard is "cold", then the symptoms may not appear.

Can you temporarily connect a different power-supply, to see if that resolves the problem when the motherboard is "warm" ?

Your only solution might be to replace the motherboard -- more expensive than first trying a different power-supply.