So, AT power cable colors and stuff? (orange/power good)

[Killbat]

What's the orange wire from an AT power supply? It's labeled "PG" on the power supply's board, and it runs to a little extension PCB labeled "PG Part", which has a 14-pin DIP and some assorted parts on it. Whatsit? Is it expendable?

[edit]Ah, it says in this 386 board manual that it's "Power Good". So, what do I do with it? Should it be tied high/low? Can it be left off?

[edit]OK, I can boot a 486 board with only +5 and +12. I CAN'T boot without the "Power Good" wire connected. What do I do to get around this? HELP!

[edit]OooooK, I see that "PG" looks like +5v, but it's drawing only 0.1ma! Is it data? Is it safe to tie it to the +5v power line without frying the board?

[edit]Tying it to +5v doesn't work. I can't figure out how to cheat this thing. Please, any ideas?

 

[Killbat]

^

 

[Mark R]

The Power good signal tells the motherboard that the power supply output voltages have settled into their working range and that the PSU is operating correctly. Only once the motherboard receives the power good signal does it energize the main circuits, eg. CPU etc.

You could tie the PG signal high, but you may find that your system doesn't boot reliably, as the motherboard tries to energize circuits before the supply voltage has risen to a high enough level.

If you really need to boot with a PSU without this line, then you could attach this signal on the motherboard to a SPDT switch connected to ground and +5V. Switch the switch to provide 0 volts. Turn on the PSU. About 1 second later, flip the switch to 5 V. The system should then boot.

 

[Killbat]

OK, thanks for the info, but I can't cheat it. Even if I connect PG to the actual PG line after about a second, it won't start up.

 

[Killbat]

OK, I got it! For those wanting to know: PG is low at powerup. It MUST be tied to ground to get the signal low enough. Then, once the power is good to go, it's set high, to +5v. So, if I power on with PG grounded, as soon as I move it over to +5v, the system POSTs. The only trick is, the line has to be forced low enough by connecting to ground. Looks like I'll be running this computer on portable power in no time!