Some brilliant ATX need a dummy load to stabilize.
So I've cobbled up 2 automobile lamps -- soldered -- to a female Molex connector.
(12V and 5V)
That's enough to get the smartest PSUs to fire up all rails.
RAIL = DC VOLTAGE VALUE
Red = + 5.0 VDC
Orange = + 3.3 VDC
Yellow = + 12. VDC
Black = 0 VDC -- the return conductor
The other whips constitute either legacy negative rails -- not used on any daughter card in the last quarter-century -- or are essential for smart switching of the PSU by the MSFT Windows program.
Purple = + 5 VDC -- hot at all times limited amps: Standby
Green = + 5 VDC (fed by purple rail) during PC - 'off'
It's fed across a (stiff) resistor... and swings HIGH when its path to ground is broken -- the 'off' state for the PC.
Should you physically short this conductor to ground (any black) its new Boolean value ("0") triggers the PSU to spool up to full output -- specifically the +12 VDC and + 3.3 VDC rails. { with the smarter PSUs insisting on a load from the + 12 VDC rail -- ie CD-ROM drive/ HDD/ FDD. (If all three are missing then the shorted signal is a false one, and the PSU STILL won't fire up. This feature is not a universal one.)
Brown + 3.3 VDC feedback detection circuit. This puppy is typically snuck into the Molex connector. It's a totally 'unloaded' run of +3.3 VDC power that permits the latest brainy motherboards to evaluate and adjust the voltage drop hitting the memory and CPU rails. Beyond a certain threshold the voltage gap -- at the motherboard end between this conductor and the orange rail (the power run at +3.3 VDC ) will cause the CPU to instantly shut down -- without any notice at all. This is to preserve the 'machine state' -- data quality -- so that the PC does not run-on with flakey memory values. The brown conductor will appear to be seriously undersized. It's carrying virtually no actual current. Think of it as a perpetual DMM running in the backround.
Gray = Actually an analog-Boolean time-delay value. This, like brown, 'talks' to the CPU and memories. It's a delay line in their Boolean start up logic. It stops them from even beginning to load digital information until the +3.3 VDC 'rail' is steady and sweet. The designers could've simply put a time-delay sequence on the motherboard. Instead they've elected to force the PSU to tell the motherboard that enough time has elapsed -- AND -- verify that the + 3.3 VDC is sweet and stable; all of the capacitors are saturated with a DC potential.
Yet later designs have dropped much of the above -- and deliver +12 VDC only. This drastically simplifies the PSU -- as the CPU voltage is provided by a DC to DC power supply right next to the CPU on the board.
It's this element that has all of the big caps soldered in parallel from the Pentium 4 and onwards... which is another story.
