My 3–4-year-old self-built PC suddenly powered off a few days ago, and I noticed a faint burnt-electronics smell. After letting it sit and trying again, pressing the power button produced no response at all.
I initially suspected the 450W Corsair SFX power supply, so I tested the system with a different 650W Seasonic SFX unit, but the PC still would not start. The components are a Biostar B550M Silver ITX motherboard, Ryzen 5 5600X, Gigabyte RTX 4070, Noctua NH-L9A cooler, two SSDs, and two case fans in a Fractal Node 202. The old PSU was probably operating with fairly little headroom for peak CPU and GPU power draw, although it had worked without trouble until now.
After disassembling the system, I found a dark, sticky-looking residue or discoloration on the back of the motherboard, directly behind the CPU VRM area. It does not wipe or scratch off, and there is no other obvious physical damage. The back of the board sits very close to the case, so I wondered whether heat from the VRMs could have damaged it.
Does this look like heat damage or a failed motherboard component? I also tested with only the PSU, motherboard, CPU, cooler, and power switch connected, but there was still no fan movement or other response. If the motherboard is dead, how likely is it that the CPU survived?
2 Answers
The dark patch could also be a failed MOSFET or capacitor in the VRM section, especially given the burnt smell and the fact that the system is completely unresponsive. If a component there actually burned, the motherboard should be considered unsafe to keep testing.
The CPU may have survived; motherboard failures do not automatically kill the processor. The only reliable way to know is to test the 5600X in a known-good compatible board after replacing the failed motherboard.
The residue does not necessarily mean the board overheated. It may be oil or compound from the thermal pad on the other side of the motherboard seeping through the vias around the VRM area. That can look ugly while still occurring at perfectly normal temperatures.
The complete lack of response does make a dead motherboard plausible, but the residue alone is not enough to diagnose a blown component. The usual next step is a bare-minimum test: connect only the motherboard, CPU and cooler, PSU, and the case power-switch header. Disconnect the GPU, drives, fans, USB headers, and everything else, then check whether the board shows any signs of life.
I tried that configuration as well, using only the PSU, motherboard, and CPU, but pressing the power button still produced absolutely no reaction. I am probably going to replace the motherboard and hope the CPU is still functional.