MSI B450i Gaming Plus AC - MS-7A40 Ver 2.0 - not powering on

[lalle-]

Hello!

I have a problem with a MSI B450I Gaming Plus AC motherboard.
I bought it as defective, thinking it was an easy fix. It turns out it wasn't (for me at least).

Problem: The board does not power on when shorting the PWR_SWITCH pins. No sign of life what so ever.
What I've tried:
I downloaded the latest non-beta BIOS from MSI's website and flashed it manually with a ch341a programmer.
Installed only a compatible CPU - Ryzen 3 2200G, nothing more, no peripherals connected.
Measured resistance on the ATX power connectors - no shorts, but perhaps a little low resistance on the +5V line (570ish Ohms to COM)
Visual inspection of the motherboard shows no obvious signs of damage.
There are 3.3V present between the PWR_SWITCH pins.

I became a little desperate/brave/stupid and jump started the PSU while connected to the motherboard.
This caused the CPU fan to start spinning and the EZ debug CPU LED to turn on, constant white light.
Tried connecting it to a monitor via HDMI, but it gave no signal.

I found the schematics in another thread: https://www.badcaps.net/forum/troubl...ics-board-view
I don't really know where to start troubleshooting this, any pointers are very welcome.

Kind regards
Lalle

[anikin73]

tell you a good news...i had repaired this model many times.....especially no startup. this board easy for broken /burnt copper traces.
1) try to trace whether IO to PSON is connected ?
2) check IO PSON is brought to 0V when u switch on.
3) check the standby voltage are no before you switch on.

[lalle-]

tell you a good news...i had repaired this model many times.....especially no startup. this board easy for broken /burnt copper traces.
1) try to trace whether IO to PSON is connected ?
2) check IO PSON is brought to 0V when u switch on.
3) check the standby voltage are no before you switch on.

Thank you for your reply!
I checked the trace from the ATX connector to the NCT6795 and it does seem to be broken. I guess I will get a chance to practice my micro soldering skills and patch that sucker up
I will update this thread once I've had the time to try to fix the connection.



Thanks again!
/ Lalle

EDIT: I might have jumped to conclusions. Looking at the schematic, the resistor I thought carried the signal seems to be a no-mount, and the signal is controlled through an NMOS. I'll have to investigate some more.