24 Pin ATX Question

TooMuchMario · February 26, 2021

I am in the process of diagnosing what is wrong with a motherboard, I probably should I have tossed it days ago but I am invested. I came across one particular pin on the 24pin ATX socket on the motherboard that does not show any continuity with the rest of the board, the -12V or blue wire on the 24 pin connector. What is this used for on the motherboard?

mariushm · February 26, 2021

There's a pin that's not used anymore in the 24 pin connector, but it's actually -5v . It was used in the past in ISA slots, so it's no longer needed... it got deprecated in the latest atx standard specifications.

-12v is still part of the standard, but probably nothing bad would happen if it's missing, and it wouldn't surprise me if some motherboards don't connect the pin in the header to anything.

It's only used for serial ports, for example if you connect your computer to the serial port of a network switch with management instead of using web interface or whatever. A lot of motherboards don't have those serial ports on the back, only as headers or none at all ... and there's lots of usb serial adapters these days.

TooMuchMario · February 26, 2021

5 minutes ago, mariushm said:

There's a pin that's not used anymore in the 24 pin connector, but it's actually -5v . It was used in the past in ISA slots, so it's no longer needed... it got deprecated in the latest atx standard specifications.

-12v is still part of the standard, but probably nothing bad would happen if it's missing, and it wouldn't surprise me if some motherboards don't connect the pin in the header to anything.

It's only used for serial ports, for example if you connect your computer to the serial port of a network switch with management instead of using web interface or whatever. A lot of motherboards don't have those serial ports on the back, only as headers or none at all ... and there's lots of usb serial adapters these days.

I see, so I should not be worried about this pin being the problem if the motherboard was getting power to fans but not usb or display?