Question Old PC Stopped Booting

martinch

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Mar 21, 2014
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Hi all,

My parents' PC has started playing up, and I'm a bit stumped as to what's wrong with it.

When you press the power button, the following happens:
  1. The power LED on the case illuminates
  2. The case fans (front and rear) spin up
  3. The CPU fan twitches, and the CPU debug LED briefly blinks on-off once (<0.5s)
  4. The power LED on the case goes off
  5. The case fans stop
  6. Go to step 1
I've taken the side of the case off, and whilst the CPU fan isn't spinning up, it does spin freely if a bit notchy should you flick it. There's nothing displayed on the screen, and I think I can hear the PSU fan starting to spin.

The PC's spec is as follows:
  • Intel Core i3-4330
  • ASUS Z87-A motherboard
  • 8GB Corsair Vengeance LP 1600MHz DDR3 (2x4GB)
  • Seasonic G-Series 450W PSU
  • Crucial MX500 SSD
  • Fractal Design Define R4 case
The PC hasn't been tinkered with since it was built in 2014, other than to switch the original HDD for an SSD a few years ago, and was working this morning.

Any ideas as to what I should be looking at/the most likely culprit gratefully received! I've tried removing the CMOS battery, which made no difference.

Thanks!

P.S. I don't have any spare parts to do the obvious swap tests.

++ EDIT for clarity on chronology of events
 
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martinch

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Mar 21, 2014
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If the CPU cooler's fan doesn't spin, the CPU will shut down on high temp.
Whilst that's true, I don't think the CPU fan has failed, as it'd normally halt at the BIOS with a low fan rpm warning, rather than immediately boot-looping after less than 5 seconds. On a normal boot, the case fans spin up, and then the CPU fan spins up (to high-ish RPM before dropping to something sensible - seems to be a quirk of that board) - it's not quite getting to this point.

I guess today's job is to pull the PSU and test the various lines are within spec...
 

clutchc

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Whilst that's true, I don't think the CPU fan has failed, as it'd normally halt at the BIOS with a low fan rpm warning, rather than immediately boot-looping after less than 5 seconds. On a normal boot, the case fans spin up, and then the CPU fan spins up (to high-ish RPM before dropping to something sensible - seems to be a quirk of that board) - it's not quite getting to this point.

I guess today's job is to pull the PSU and test the various lines are within spec...
Well, you said "the CPU fan isn't spinning up (it twitches slightly, but that's it ". That would indicate to me that the fan isn't working. Might have lost magnetic center or voltage is too low to start it. Normally needs +5V to start.

As to voltage testing, you should be able to read volts with a multimeter right at the 24-pin connector with it connected. Just probe the wire insert holes until you touch conductor.
 

martinch

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Mar 21, 2014
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Well, you said "the CPU fan isn't spinning up (it twitches slightly, but that's it ". That would indicate to me that the fan isn't working. Might have lost magnetic center or voltage is too low to start it. Normally needs +5V to start.
Perhaps I could have worded it better - the fan twitching seems to happen immediately before it boot/power-loops, and as the CPU debug LED blinks, as though it's failing a check, or drawing too much current at that point (I've edited the original post for clarity). I can always check it, though.

As to voltage testing, you should be able to read volts with a multimeter right at the 24-pin connector with it connected. Just probe the wire insert holes until you touch conductor.
Cheers. I meant to look at the PSU today, but didn't get time (also, unplug and re-plug everything in case a connection's gone bad) - will definitely do it tomorrow.
 
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martinch

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Mar 21, 2014
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I was going to pull the PSU out and test it with a multi-meter today, but something was bugging me about how it was restarting after attempting to spin the CPU fan up, as though the PSU was unable to supply enough power for the load, so I:
  1. Tried to start the PC to verify it was still misbehaving - same behaviour as in the first post
  2. Unplugged all of the modular power cables from the PSU, leaving just the motherboard, RAM, CPU, and CPU cooler powered, and powered on the PC - it booted.
  3. Plugged in the power cable that ran to the case fans, and powered on the PC - it booted
  4. Plugged in the power cable that ran to the SSD, and powered on the PC - it booted
  5. Plugged in the power cable that ran to the optical drive (so everything is now powered), and powered on the PC - it booted
So, I'm now looking at a working PC, although I'm not sure what the issue was. Certainly, the power cables were well-seated before (I gave them a wiggle and push to make sure they weren't loose previously).

According to the BIOS (which I know is not wonderfully accurate), the voltages are:
  • 3.3V: 3.408V (3.3% from "perfect", and within the 5% ATX spec tolerance)
  • 5V: 5.04V (<1% from "perfect")
  • 12V: 12.384V (3.2% from "perfect", and within the 5% ATX spec tolerance)
Whilst the 3% deviation from spec is a bit higher than I'd like for a decent PSU, it should still be fine (I know the reviews say the regulation of the G Series is less effective at low loads, which sitting in the BIOS would qualify as).

I figure if it does it again, I'll drop a Corsair TX550M in, as it's cheap, good, and available (and as a worst case, I end up with a decent spare PSU). If it continues after that, I may end up looking at an i3-10100 or Ryzen 3 3300X, motherboard and RAM (PC runs Linux Mint, so no licensing issues from changing components) ...
 
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clutchc

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Good to hear the system is at least back to working, although it would be nice to know what was the problem in the first place, right? But you did the troubleshooting correctly, so you know what you're doing.
Good luck and stay healthy.
 
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