Question Two mobos unresponsive when CPU installed, but without CPU the mobos respond with the EZ Debug CPU light ?

Aug 13, 2022
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I have two MSI motherboards, the B450M PRO-VDH MAX and the B550M PRO-VDH WIFI. When I test bench them with just the PSU connected they appear to power up, PSU fan spins, and the EZ Debug light stays on "CPU". When I install the CPU on both mobos they are then both unresponsive, no PSU fan spin or EZ debug lights. I tried testing the mobos with other parts installed like Ram stick, m2 SSD, and they both respond with and stay on the CPU EZ Debug light, but if the CPU is also installed they are then totally unresponsive.

Both mobos may be damaged and malfunctioning, as the B450M was a replacement for the B550m when it appeared to have stopped working. The B450M worked for a while but then also appeared to have stopped working, and I apparently fried my GPU when I was trying to get the PC working again by trying both mobos with all parts connected, and I don't remember which mobo the GPU was in when it apparently fried. The Debug lights on both mobos would then go through CPU and stopped on VGA, leading me to assume it was the GPU that is dead and the other parts may be fine, so they all went into their boxes for storage until I could acquire a new GPU.

Now that I have the replacement GPU I am not connecting it to either of the mobos to be safe and first checking them without the GPU, and so am currently experiencing this CPU Debug light issue. Even if I connected the new GPU I am pretty sure the mobos would still not respond because of the CPU being connected. At first I thought it's most likely both the mobos are now toast, second most likely is the CPU is now toast, then possibly the PSU being partially toast. I don't see any burns or signs of damage on either of the mobos or the CPU, no bent pins, RAM seems fine, SSD I know works for sure, PSU passed the paperclip test.

I was going to order a new mobo or CPU but would like some opinions and advice first please. After some research it seems like if it was the CPU that was truly toast, then the mobos would light up the CPU debug light indicating it, and since they do nothing at all with CPU connected, could it be the PSU being partially toast and not supplying enough power? Right now it seems to me that it could be either the CPU, mobo, or PSU that needs replacing, maybe two or all of them. I figured it would be best to start with buying a new mobo to see, given the circumstances. Any assistance will be greatly appreciated.

Thank you for your time.

These are my parts (my first build), unfortunately don't have access to spare ones other than the 2 possibly toast mobos and a toasted and non-toasted GPU. https://pcpartpicker.com/list/TZNNsL
 
I have two MSI motherboards, the B450M PRO-VDH MAX and the B550M PRO-VDH WIFI. When I test bench them with just the PSU connected they appear to power up, PSU fan spins, and the EZ Debug light stays on "CPU". When I install the CPU on both mobos they are then both unresponsive, no PSU fan spin or EZ debug lights. I tried testing the mobos with other parts installed like Ram stick, m2 SSD, and they both respond with and stay on the CPU EZ Debug light, but if the CPU is also installed they are then totally unresponsive.

Both mobos may be damaged and malfunctioning, as the B450M was a replacement for the B550m when it appeared to have stopped working. The B450M worked for a while but then also appeared to have stopped working, and I apparently fried my GPU when I was trying to get the PC working again by trying both mobos with all parts connected, and I don't remember which mobo the GPU was in when it apparently fried. The Debug lights on both mobos would then go through CPU and stopped on VGA, leading me to assume it was the GPU that is dead and the other parts may be fine, so they all went into their boxes for storage until I could acquire a new GPU.

Now that I have the replacement GPU I am not connecting it to either of the mobos to be safe and first checking them without the GPU, and so am currently experiencing this CPU Debug light issue. Even if I connected the new GPU I am pretty sure the mobos would still not respond because of the CPU being connected. At first I thought it's most likely both the mobos are now toast, second most likely is the CPU is now toast, then possibly the PSU being partially toast. I don't see any burns or signs of damage on either of the mobos or the CPU, no bent pins, RAM seems fine, SSD I know works for sure, PSU passed the paperclip test.

I was going to order a new mobo or CPU but would like some opinions and advice first please. After some research it seems like if it was the CPU that was truly toast, then the mobos would light up the CPU debug light indicating it, and since they do nothing at all with CPU connected, could it be the PSU being partially toast and not supplying enough power? Right now it seems to me that it could be either the CPU, mobo, or PSU that needs replacing, maybe two or all of them. I figured it would be best to start with buying a new mobo to see, given the circumstances. Any assistance will be greatly appreciated.

Thank you for your time.

These are my parts (my first build), unfortunately don't have access to spare ones other than the 2 possibly toast mobos and a toasted and non-toasted GPU. https://pcpartpicker.com/list/TZNNsL
With those symptoms could be any of those parts but the start should be with known good and compatible PSU.
MB appears to have power without CPU but not with it can also mean that VRM is shot.
 

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