Z820 can’t boot, four red beeps after fan revving

[stig8]

My Z820 was fine yesterday, before sleeping I put it to hibernation but then it can‘t wake up, with four red blinks on the start button and in the back. According to the manual it is a psu overload issue so

1. I took the psu out and plug it directly to wall, green led and fan was running, seems like not a faulty psu issue

2. I put the psu back but unplugged the main power supply cable on motherboard, psu green light, so maybe this can rule out loose cable behind the motherboard? Tried removing the right panel but it is so stuck I think I could not take it out without bruteforce.

3. I plugged back the main power supply but removed stuffs on the motherboard, memories, graphic card, fans, hard drive, cpu power cables . The only thing left was my two cpus. Then I plugged the box back to wall, still four beeps.

During the above diagnosing I also tried pushing the bios reset button, swapping a new cmos battery and vacuuming dirts accumulated in the box. Do I need to try replacing the cpu? Or is it a motherboard issue? Thanks in advance .

[Bill_To]

Hi @stig8 

Welcome to the HP Forum.

The Service guide for your PC provides the Following:

It sounds like a power supply, CPU, or MB problem.

Regards

[stig8]

Hello Bill. I took my cpus off and powered the motherboard(without any devices on it), three red blinks indicating no cpu as intended. Then I put a cpu to cpu0 socket, it turned to four blinks. I’ve tried my other cpu but no luck. So is it a cpu issue or motherboard issue? Thanks!

[Bill_To]

Hi @stig8 

My pleasure.

The power supply BIST you did seems to indicate the power supply is okay. But I always refer to the auto battery analogy; you can listen to the radio but you can't start the engine.

You got a different error code with no CPUs installed in the system board. This seems to indicate the board is getting power. But then, is the MB getting enough amps to POST?

It would be very unusual to see two CPUs fail at the same time, so maybe a PSU or MB problem?

Sorry, I still see no clue as to what component is in trouble. You might have to swap in components to find the bad part or try your components in a different PC.

It costs money to swap in components. Maybe a local PC Tech can do this at a fraction of the cost.

Regards