Question Will the Mobo boot with the CPU power in but not the CPU itself?

Nov 28, 2021
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Trying to figure out if my CPU is fried. My PC began not starting up, upon switching on front case switch, it would flash the lights inside and then something after a split second told the PSU to shut down.

I tested the power supply and it looked as if it still worked, tested using switch pin on main board power supply, paperclip bridge etc.
The power supply works.

I then took the computer apart completely, took mobo out of case, set it up as a workbench from scratch and I can start the mobo without any CPU, RAM, GPU, M.2 SSD connected. The board itself will not tell the PSU to shut down, it will start upon shorting the power switch pins. But debug light will land on CPU , meaning "CPU Not found"
Makes sense.

If I put in the CPU but dont connect the power to the 8 pin CPU power CPU Pwr1, it will start and board give me the same CPU debug light, not shutting down PSU

If I put in the CPU but dont connect the power to the 8 pin CPU power CPU Pwr1, and I put in a RAM module it will start and board give me the same CPU debug light, not shutting down PSU

If I put in the CPU and do connect the power to the 8 pin CPU power CPU Pwr1, the PSU will start split second, make a click sound and immediately shut down
If I don't put in the CPU and do connect the power to the 8 pin CPU power CPU Pwr1, the PSU will start split second, make a click sound and immediately shut off

So it would seem that it will still shut down the PSU (Not start) regardless if the CPU is there or not, it only needs that CPU power connected and PSU will shut off.

I have tested all voltages outgoing from the PSU they are all correct, the power out of every +12v pin in the CPU power cable is 12.10V on multimeter.

This has happened to me on two different motherboards MSI B450M Mortar Titanium and MSI B450M Mortar Max (Replacement board I bought yesterday) which I understand are the same board just different paint styles

I have also tested with two power supplies 650W and one I have is 18 months old and the other brand new. Both PSUs pass all tests on multimeter and paperclip starts.

Tried remove CMOS Battery,
Tried also CMOS Reset bridge the reset jumpers

So my question is, the only part I have not replaced is the CPU, but before I buy a CPU to test it out, I keep hearing "CPU rarely is the failure" well would it be so RARE that it would be more likley that two motherboards are both failing, even the new one?

Still it doesn't explain why the board still wont start with the CPU out, but the CPU power cable in. This is where someone who knows the circutry of the motherboard may be able to help, and my topic title "Will the Mobo boot with the CPU power in but not the CPU itself? " when I say this I mean any mobo, is it normal that a mobo will start with only the main power cable attached, but not the main power cable and the cpu cable?

This would greatly help me know whether I should buy another CPU or another Mobo

First time poster, go easy
TIA

PC: Ryzen 5 3600
MSI Mortar Max B450M and MSI Mortar Titanium B450M
4 x 8GB Corsair DDR4 Vengeance LPX RAM Chips
1 x NVME Samsung SSD m.2
1 x EVO Samsung SSD m.2
Gigabyte RTX 2060 Super OC 8Gig GPU
Cooler Master MWE 650w Gold PSU
Silverstone 650W Strider Gold S PSU

Bold items are new replacements, which didn't solve issue
 
Last edited:
Trying to figure out if my CPU is fried. My PC began not starting up, upon switching on front case switch, it would flash the lights inside and then something after a split second told the PSU to shut down.

I tested the power supply and it looked as if it still worked, tested using switch pin on main board power supply, paperclip bridge etc.
The power supply works.

I then took the computer apart completely, took mobo out of case, set it up as a workbench from scratch and I can start the mobo without any CPU, RAM, GPU, M.2 SSD connected. The board itself will not tell the PSU to shut down, it will start upon shorting the power switch pins. But debug light will land on CPU , meaning "CPU Not found"
Makes sense.

If I put in the CPU but dont connect the power to the 8 pin CPU power CPU Pwr1, it will start and board give me the same CPU debug light, not shutting down PSU

If I put in the CPU but dont connect the power to the 8 pin CPU power CPU Pwr1, and I put in a RAM module it will start and board give me the same CPU debug light, not shutting down PSU

If I put in the CPU and do connect the power to the 8 pin CPU power CPU Pwr1, the PSU will start split second, make a click sound and immediately shut down
If I don't put in the CPU and do connect the power to the 8 pin CPU power CPU Pwr1, the PSU will start split second, make a click sound and immediately shut off

So it would seem that it will still shut down the PSU (Not start) regardless if the CPU is there or not, it only needs that CPU power connected and PSU will shut off.

I have tested all voltages outgoing from the PSU they are all correct, the power out of every +12v pin in the CPU power cable is 12.10V on multimeter.

This has happened to me on two different motherboards MSI B450M Mortar Titanium and MSI B450M Mortar Max (Replacement board I bought yesterday) which I understand are the same board just different paint styles

I have also tested with two power supplies 650W and one I have is 18 months old and the other brand new. Both PSUs pass all tests on multimeter and paperclip starts.

Tried remove CMOS Battery,
Tried also CMOS Reset bridge the reset jumpers

So my question is, the only part I have not replaced is the CPU, but before I buy a CPU to test it out, I keep hearing "CPU rarely is the failure" well would it be so RARE that it would be more likley that two motherboards are both failing, even the new one?

Still it doesn't explain why the board still wont start with the CPU out, but the CPU power cable in. This is where someone who knows the circutry of the motherboard may be able to help, and my topic title "Will the Mobo boot with the CPU power in but not the CPU itself? " when I say this I mean any mobo, is it normal that a mobo will start with only the main power cable attached, but not the main power cable and the cpu cable?

This would greatly help me know whether I should buy another CPU or another Mobo

First time poster, go easy
TIA

PC: Ryzen 5 3600
MSI Mortar Max B450M and MSI Mortar Titanium B450M
4 x 8GB Corsair DDR4 Vengeance LPX RAM Chips
1 x NVME Samsung SSD m.2
1 x EVO Samsung SSD m.2
Gigabyte RTX 2060 Super OC 8Gig GPU
Cooler Master MWE 650w Gold PSU
Silverstone 650W Strider Gold S PSU

Bold items are new replacements, which didn't solve issue
How were you running the system before it failed on you? Any conventional overclocking? PBO? What kind of cooling?
 
Dec 5, 2021
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Could be two things, processor or ram, RAM tends to be the most troublesome, even placing them incorrectly can cause your PSU to do that kind of stuff, so check your rams first, try to get a friend that can reach you at least a single stick of ram to test it out before buying a entire new CPU.
 

Lafong

Respectable
Dec 2, 2021
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Are you positive you have the 8 pin CPU power cable rotated to the correct orientation?

The connectors at the end of the cable may or may not be keyed to fit only one way?

I have personally seen power supplies on which the plug at the end of that cable was installed incorrectly at the factory, leading to incorrect orientation when attempting to use the PSU.
 

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