Question System has stopped booting up, with only CPU + mobo + PSU

jugdish

Commendable
Jan 18, 2019
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First off, I have already read and followed the instructions in the "No POST" sticky thread. In general I found it more aimed at new builds that aren't powering on and have never powered on, whereas my system has been running fine for almost 7 years and suddenly stopped last Sunday.

The system is a Linux machine built by me, running Ubuntu 20.04 as a headless server. I interact with it via SSH and NoMachine only. On Sunday I kicked off a CPU intensive task -- computing a machine learning model -- which was going to take ~8 hours of 100% CPU to complete. I went out for a couple hours and when I came home the machine was not running. It wouldn't boot back up. I connected a monitor to its DVI port and there was no display when powered on.

So I took out all of the components, even the memory, leaving only these parts still connected:
ASRock FM2A85X-ITX motherboard
AMD A10 6700T CPU
Scythe Big Shuriken 2 heatsink
picoPSU-120 power supply

What does happen: The power supply LEDs light up (both the red and green LEDs on the picoPSU), the front panel LEDs light up, the case fan turns on. The heatsink fan runs sporadically, a few rotations, then stops.
What doesn't happen: no display on the monitor, no BIOS screen, no beep on the system speaker.

My first instinct is that I killed the CPU from overheating. The power supply is only 120W, and I have noticed the HSF is often not spinning at all, and when it does it is in fits & starts. I don't know if this is malfunction, a sign of inadequate power, or simply the BIOS dynamically managing fans based on temps. But what I've been reading on other posts is that apparently it is rare for a modern CPU to die from overheating due to the failsafes and protections in place to prevent that. So even if the HSF is unreliable, the system should shut off before the CPU dies.

It seems very strange that I get no beep codes through the system speaker, even though I've removed the memory. Other posts I've read indicate that usually means the power supply is dead. But as I've said, the PSU appears operational since its LEDs come on and the case fan spins.

Any ideas of what I should try next?
 
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vov4ik_il

Respectable
Ehm… it will 100% not POST without RAM.
P.S those pico psu boards go bad easy, hook something known-working instead to verify. The LED on the PSU and the case fan does not mean much, there are 4 essential voltages for the board to work, and the +12v is just one of them.
 
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jugdish

Commendable
Jan 18, 2019
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With the RAM removed I'm no longer expecting it to POST, I'm expecting it to beep. I was hoping for the system speaker to show some sign of life and alert about the lack of memory, but nothing.

I guess based on your suggestion it sounds like I should replace the PSU first of all, before replacing the motherboard or CPU. The timing of this is suspicious though, because it happened during a prolonged period of 100% CPU, something that I would expect to tax the CPU not the PSU.
 

jugdish

Commendable
Jan 18, 2019
7
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A PSU providing correct voltages when under no load whatsoever merely tells you it is capable of exactly that...(functioning under zero load)

(Not even close to the same as indicating PSU is good)

Trying another known good PSU would be an essential first step...(If your original and possibly bad PSU is modular, do NOT mix/match cables from the old PSU with the new/different one for testing purposes...not even for an instant!
 

vov4ik_il

Respectable
Those voltage numbers are meaningful only if you can measure it when it is plugged into the system you are trying to start. It is a switching PSU and in open circuit conditions it might work even with dead caps.
 

jugdish

Commendable
Jan 18, 2019
7
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1,510
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A brand new Corsair SF450 PSU just arrived today. I hooked it up to my system and got the exact same result: case fan + CPU fan spin, LED lights come on, but no display and no speaker beep. So I think we can rule out the power supply as the culprit.
 

jugdish

Commendable
Jan 18, 2019
7
0
1,510
0
Pls go to basics:
CPU, 1 stick of RAM, GPU and CPU fan, hooked up to the PSU, nothing else. If it beeps/posts - great, if not, reset CMOS and try again, otherwise, it might be a bad board.
Yes, that's what I'm doing -- I have only the CPU, 1 stick of RAM, and motherboard (with integrated graphics) connected to the PSU. I removed the CMOS battery completely. There is no beep, even after waiting for a full minute after power on.
 

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