PlayStation Development Network

The PU-8 mainboards (SCPH-1000) have a 7pin power supply connector (unlike later boards with 5pin connectors). One of the extra pins is just another GND pin. The other one is +3.5V standby, ie. that pin is powered even when the console is switched off. What is THAT for?

From what I can see (when gazing at the PCB), the standby voltage seems to be left unused (on the PU-8 board, it seems to be connected to GND via a SMD capacitor, but doesn't appear to be connected anywhere else).
Maybe older PU-7 boards did use it... to power something on the mainboard... or to power something on the Parallel I/O port... or Sony was using the same power-supply board also for hardware other than playstation?

It could have been left in their design as an extra voltage rail should they have needed in the future a device being powered on standby. They could have also intended to have a 3-way RGB LED. Red/yellow for off and or standby, and green for power on, much like the PS3 and PS3 power light.

I have a playstation but I dont have the idea what is PSX standby voltage