I can speak with direct experience (because they are nearby) of the passive power-control, or, in Apple's parlance, 'pseudo-soft power-on', in the CC/P250, 5400, 5500 and 580. Out of the box or the cupboard where they have not been powered, the top of the case bucket, at the rear, is 'cold', or at the same temperature as the rest of the bucket. Mine have been powered-on through the rear case switch since they were set up anything up to five years ago.
It's 25°© in my study at the moment, near the end of a night of intermittent rain, with cool saturated airflow through the room. All the Macs are palpably warmer above that rear case switch than in the rest of their cases, the CC/P250s more obviously so because of their smaller dimensions. The palpability is greater during our winter, when my study gets down to 8-12°. It is just as real for the (again, passive power-control, but with no kind of soft power-on) Compact AIOs 512Ke, Classic II and SE/30 that are set up ready for switch-on as it is for the spare Classic, Classic II and SE/30 sitting, with active mains connections, on the shelf behind. The warmth is not so discernible atop the pizza-boxes of the LC II and Q605.
The dozen-odd active power-control Macs, with true soft power-on, that are also in the room are always warm, and this is most apparent in their PSU cases immediately after the Macs are opened, or in the vent area of the CRT iMacs. To the extent that their startup circuits are represented by the schematics for members of the Mac II family, it is very clear that a normally reverse-biased diode protects the 3.6-V PRAM battery from the 5-V supply to the relevant pin of their clock and PRAM ICs, PMUs or whatever.
I suspect that the battery-sparing in the Compact AIOs will be far more readily revealed as a minuscule current consumption by the powered-off Mac. In the PSU schematic for the SE and SE/30 (Bomarc), the PRAM battery is again shown as protected by a reverse-biased diode from a 5-V supply, in the absence of which it provides power on a 4-V line to the real-time clock/PRAM IC. That revelation was not the least of my reasons for getting hold of the SE/30 schematics when they were offered here Before The Fall, but only this thread has stimulated me to seek out whatever is to be found. I have yet to track down the source of the 5V (the schematics are in .pdf), which is, of course, the nub of this part of the thread. Hold your breath for a later revelation.
de
It's 25°© in my study at the moment, near the end of a night of intermittent rain, with cool saturated airflow through the room. All the Macs are palpably warmer above that rear case switch than in the rest of their cases, the CC/P250s more obviously so because of their smaller dimensions. The palpability is greater during our winter, when my study gets down to 8-12°. It is just as real for the (again, passive power-control, but with no kind of soft power-on) Compact AIOs 512Ke, Classic II and SE/30 that are set up ready for switch-on as it is for the spare Classic, Classic II and SE/30 sitting, with active mains connections, on the shelf behind. The warmth is not so discernible atop the pizza-boxes of the LC II and Q605.
The dozen-odd active power-control Macs, with true soft power-on, that are also in the room are always warm, and this is most apparent in their PSU cases immediately after the Macs are opened, or in the vent area of the CRT iMacs. To the extent that their startup circuits are represented by the schematics for members of the Mac II family, it is very clear that a normally reverse-biased diode protects the 3.6-V PRAM battery from the 5-V supply to the relevant pin of their clock and PRAM ICs, PMUs or whatever.
I suspect that the battery-sparing in the Compact AIOs will be far more readily revealed as a minuscule current consumption by the powered-off Mac. In the PSU schematic for the SE and SE/30 (Bomarc), the PRAM battery is again shown as protected by a reverse-biased diode from a 5-V supply, in the absence of which it provides power on a 4-V line to the real-time clock/PRAM IC. That revelation was not the least of my reasons for getting hold of the SE/30 schematics when they were offered here Before The Fall, but only this thread has stimulated me to seek out whatever is to be found. I have yet to track down the source of the 5V (the schematics are in .pdf), which is, of course, the nub of this part of the thread. Hold your breath for a later revelation.
de