Question Computer doesn't turn on, then turned on alone

[Uayvie]

Hello everyone, I'll try to explain my problem as best I can, any help would be appreciated.

1. Motherboard power light is on but I can't boot up.
2. Computer randomly boot up alone and everything was fine, then I shutdown.
3. Can't boot up again.

Things I've done:

• Unmounted everything and mounted with only CPU and 1 stick of ram.
• Cleared CMOS (battery and pins).
• Tested power supply with a paper clip.
• Boot from motherboard (bridging pins), no response.

 

[PassMark]

The paperclip method of testing power supplies isn't very effective. Power supplies need to produce a bunch of different voltages, within a bunch of different precise timings, with the right sequence and then keep it all stable.

Failure to do this will cause the machine not to boot or boot intermittently. Diagram of timings and sequencing is below.

T1 < 500 ms
0.1 ms ≤ T2 ≤ 20 ms
T6 ≥ 1ms
etc.....

These are hard to measure without an oscilloscope or inline tester.

Do you have a spare power supply to try, or can you borrow one?

 

[punkncat]

Being this close to Halloween begs questions about ghosts....

What are the specs of this system?

 

[Uayvie]

The paperclip method of testing power supplies isn't very effective. Power supplies need to produce a bunch of different voltages, within a bunch of different precise timings, with the right sequence and then keep it all stable.

Failure to do this will cause the machine not to boot or boot intermittently. Diagram of timings and sequencing is below.

T1 < 500 ms
0.1 ms ≤ T2 ≤ 20 ms
T6 ≥ 1ms
etc.....

These are hard to measure without an oscilloscope or inline tester.

Do you have a spare power supply to try, or can you borrow one?

Hello PassMark, that's a very good point, I'll try to get one to test tomorrow, thank you!

 

[Uayvie]

Being this close to Halloween begs questions about ghosts....

What are the specs of this system?

😁

AMD Ryzen 5 3600X
Asus ROG Strix B450-F Gaming ATX
Corsair Vengeance LPX 16GB (2x8GB) DDR4-3200MHz
Seasonic S12III Series 650W 80PLUS Bronze
GTX 1660 Super

 

[Paperdoc]

This MIGHT be as simple as a poor On / Off pushbutton switch on the case front, OR a poor connection where its wires plug into the mobo's Front Panel header. You could try this diagnostic. The RESET button is exactly the same type. For both switches, polarity of the connections does NOT matter. At the mobo Front Panel header, identify the pins and wires for the POWER switch and the RESET switch. Unplug the wires from the POWER pins, then move the wires from the RESET pins over to the POWER pins. Now test whether using the RESET switch on the case front makes it work properly. When done, re-connect as they were to begin.

IF that makes things work, you have identified the problem. IF they STILL work AFTER you have re-connected properly, maybe you fixed a temporary poor connection. IF this does NOT solve the problem, you know the switches are not part of the issue.

 

[punkncat]

OP notes they tried shorting the front panel connector in first post.

I have had this issue be due to a failing PSU and have also had it be a bad mobo. Short of having other parts to test with it might be worthwhile to consider a local mom and pop shop or enthusiast, if you know any.

 

[Uayvie]

The paperclip method of testing power supplies isn't very effective. Power supplies need to produce a bunch of different voltages, within a bunch of different precise timings, with the right sequence and then keep it all stable.

Failure to do this will cause the machine not to boot or boot intermittently. Diagram of timings and sequencing is below.

T1 < 500 ms
0.1 ms ≤ T2 ≤ 20 ms
T6 ≥ 1ms
etc.....

These are hard to measure without an oscilloscope or inline tester.

Do you have a spare power supply to try, or can you borrow one?

Hello again PassMark, pc booted up alone again, he's on right now, should I do something while he's up? I don't have the PSU yet to test.

 

[Uayvie]

This MIGHT be as simple as a poor On / Off pushbutton switch on the case front, OR a poor connection where its wires plug into the mobo's Front Panel header. You could try this diagnostic. The RESET button is exactly the same type. For both switches, polarity of the connections does NOT matter. At the mobo Front Panel header, identify the pins and wires for the POWER switch and the RESET switch. Unplug the wires from the POWER pins, then move the wires from the RESET pins over to the POWER pins. Now test whether using the RESET switch on the case front makes it work properly. When done, re-connect as they were to begin.

IF that makes things work, you have identified the problem. IF they STILL work AFTER you have re-connected properly, maybe you fixed a temporary poor connection. IF this does NOT solve the problem, you know the switches are not part of the issue.

Hello Paperdoc, I've tested booting from motherboard (bridging the pins) and I knew this was not the problem when pc turned on alone and I could shutdown with the power button.

 

[Uayvie]

OP notes they tried shorting the front panel connector in first post.

I have had this issue be due to a failing PSU and have also had it be a bad mobo. Short of having other parts to test with it might be worthwhile to consider a local mom and pop shop or enthusiast, if you know any.

Sorry PunknCat, I couldn't understand you well, English isn't my native language, can you rephrase? Thank you.

 

[punkncat]

Sorry PunknCat, I couldn't understand you well, English isn't my native language, can you rephrase? Thank you.

You addressed part of it in reply to paperdoc.

The other was suggesting taking it to a shop.

 

[Dark Lord of Tech]

Seasonic S12III Series 650W 80PLUS Bronze ..... is a VERY VERY poor power supply. Not even made by SEASONIC.