Macintosh soft power - atx conversion

[AlpineRaven]

Asking for thoughts and on how to modify and understanding how soft power works.

My question is, once you apply power on (on the keyboard) does the power cut off and restore power? Or as soon you press it, the power feeds to psu to turn the relay on?

What about when you shut it down - how does it completely turn off the psu - is it the same circuit as soft power?

this question is prior to researching and thought I’d ask on here first in case someone could point me to right direction?

Story to relate above, I’ve just recapped Macintosh IIsi psu and made it even worse - it blew up! The caps were installed correctly, correct fuse replaced. I reckon the liquid has seeped into the pcb hence conductive.

So thought about getting small/micro atx psu around 250watts to install but would like to make it as much original as possible.

Cheers

AP

 

[techknight]

Well each mac is different but I think your referring to the IIsi here specifically? 

the IIsi has a 5V standby that stays hot all the time powering the 68HC05 that is inside the IIsi. when the power button is pressed, it brings PFW high which starts up the unit. You pull PFW low again to shut down the unit.