Hello,
So I bought a faulty ASUS PRIME B450 PLUS motherboard off eBay. They said it was water damaged and they cleaned it. The PC POSTs and displays a message that it's detected USB overcurrent and will shut off in 15 seconds. I verified this myself. So I did some checks at the ATX connector 1st to see if the resistance readings looked OK. I found the 3.3V rail measures just 179Ohms which seems way too low. It's been much higher on other AM4 boards I've worked on.
So I did some Googling to see what the potential culprits are. It varies from bad protection diodes, bad ports or even the PCH. I went to the protection diodes (they are SOT23-6) and measured the resistances on the legs against GND. All looked OK, but one. One was reading close to the Ohms I was seeing on the 3.3V rail. I attached an image of the 2 readings on the chip:
So I removed it to see if that changed anything. Unfortunately not, the resistance readings remain the same. It seems like only one port is affected. I checked the pins on the USB port at the back of the board, on 2 of the pins for one port, I get the same low ohm reading. On the other port, I don't see the same low ohm reading. The ports are USB 3.1 Gen 2. They're light blue.
Before going further with this repair, I'd like to know if this issue is perhaps being caused by the PCH since the 3.3V rail is also reading low ohms. If it is the PCH, then there's not much I can do about that. If it's not the PCH, then I can continue to find where the issue is.
Appreciate any help on this. It would've been nice if I had a boardview for this board, but couldn't find one (I've requested it in the appropriate section).
So I bought a faulty ASUS PRIME B450 PLUS motherboard off eBay. They said it was water damaged and they cleaned it. The PC POSTs and displays a message that it's detected USB overcurrent and will shut off in 15 seconds. I verified this myself. So I did some checks at the ATX connector 1st to see if the resistance readings looked OK. I found the 3.3V rail measures just 179Ohms which seems way too low. It's been much higher on other AM4 boards I've worked on.
So I did some Googling to see what the potential culprits are. It varies from bad protection diodes, bad ports or even the PCH. I went to the protection diodes (they are SOT23-6) and measured the resistances on the legs against GND. All looked OK, but one. One was reading close to the Ohms I was seeing on the 3.3V rail. I attached an image of the 2 readings on the chip:
So I removed it to see if that changed anything. Unfortunately not, the resistance readings remain the same. It seems like only one port is affected. I checked the pins on the USB port at the back of the board, on 2 of the pins for one port, I get the same low ohm reading. On the other port, I don't see the same low ohm reading. The ports are USB 3.1 Gen 2. They're light blue.
Before going further with this repair, I'd like to know if this issue is perhaps being caused by the PCH since the 3.3V rail is also reading low ohms. If it is the PCH, then there's not much I can do about that. If it's not the PCH, then I can continue to find where the issue is.
Appreciate any help on this. It would've been nice if I had a boardview for this board, but couldn't find one (I've requested it in the appropriate section).
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