PcTek9
Well-Known Member
- Reaction score
- 85
- Location
- Mobile, AL
The incredibly delicious corruptible power controller chip.
I pushed the power button and the computer did not turn on. WHY?
Well, your psu as long as it is plugged in the wall always provides a trickle current to the motherboard. It's not just a simple 120 volt 5 amp single pole single throw switch any more. These days it can be a super tiny switch, b/c it just carries a tiny bit of power back to the motherboard. The motherboard has chips on it that analyze the signal sent, and decide to turn on the pc. In other words your pc (if it's an atx or later), is NEVER off at all, ever.
Though it's a good faker. The atx engineers designed a very low power circuit that runs a bunch of systems on the computer all the time, even when it's turned off. For example: wake on lan (WOL). If you have this set to true in the bios, the computer is off but if you have a lan cable plugged in, look at the back of the pc, even powered off those lan lights are on, and the motherboard is constantly looking for a signal to turn on - FROM THE LAN.
There are many such systems integrated into the new designs. WOM (wake on modem), WOK (wake on keypress), WMC (wake on mouse click) and so on... It's funny to me that people who have mouses that have lights in them that are usb powered are always saying "how come my mouse stays lit up even when the pc is off?" - then I have to explain why.
There is a whole group of circuit logic systems allocated to this! It even includes the southbridge (wake on usb keyboard, wake at a certain time of day and date, wake on a request from the pci bus, even wake on super i/o notifications such as a ring on the serial port (wake on modem) and the ps/2 ports too!!!
So anyway, we came a long long way since the old days, when the 120 or 240 volts was turned on and off to the psu. Now the psu's special low power always on subsystem command monitoring bus is always running and tightly integrated into nearly every aspect of the computer itself.
Pin 9 on your motherboards power supply main cable is the +5 VSB (5 volt standby). Push the button, and it momentarily closes (or opens) a circuit which causes the power controller chip on the motherboard to go "o yay we got a signal to do something."
Some motherboards try to remember if the system is on or off by saving some little data somewhere in a volatile ram on this power controller chip that way when they get the button press they know whether to:
1.) turn on the pc if it's actually off.
2.) turn off the pc if it's actually on.
3.) if the signal continues for a long period, clear the memory of the power controller chip and reset the psu status.
so for example, if you quickly press and release the button, if the pc is off, then the pwc sends a signal to pin 16 on the motherboard connecter ( the green wire ) which is called Power Supply On, as you would suspect, this turns on the psu.
Now, please do not be confused. The PSU ALWAYS has that other tiny trickle power running to all those different systems on the computer, the network card, the modem, the keyboard, the mouse, usb, etc. etc. I guess a better way to say this would be to just say "This turns on the 'big' power which brings up the system.".
When the computer is running in full operation there is a 5 volt signal (positive with respect to chassis ground) on the pwr_good line and that is the gray wire pin number 8 of the motherboard connector.
Now for the easy fun stuff... Every motherboard maker felt free to design these new power circuits anyway they pleased, there's no standard that I am aware of... Some simply use a simple pnp junction field effect transistor as an interface to a motherboard power connector pin, since the logic is the same it works by allowing the transistor to directly drive the signal.
Other mother board manufacturers use custom power chips that have pins going out of them all over the motherboard to provide a tiny computer that controls the entire psu "rise and shine" function.
So... Is it any wonder that if the little microcontroller which is supposed to remember if the pc is already on or not (maybe your configuration actually stores a bit in the escd to indicate the current status?), if that got confused - whether in ram or live in the microcontroller itself (which is always on and being powered even when the pc or laptop is shutdown), that option 3.) push & hold might be necessary? Sometimes, even the little microcontroller is so confused you have to remove all power to the thing so it can allow everything to reset.
You can also use the other method of unplugging it and waiting a few months for all the caps to completely drain. (LOL). That's definitely another technique.
I pushed the power button and the computer did not turn on. WHY?
Well, your psu as long as it is plugged in the wall always provides a trickle current to the motherboard. It's not just a simple 120 volt 5 amp single pole single throw switch any more. These days it can be a super tiny switch, b/c it just carries a tiny bit of power back to the motherboard. The motherboard has chips on it that analyze the signal sent, and decide to turn on the pc. In other words your pc (if it's an atx or later), is NEVER off at all, ever.
Though it's a good faker. The atx engineers designed a very low power circuit that runs a bunch of systems on the computer all the time, even when it's turned off. For example: wake on lan (WOL). If you have this set to true in the bios, the computer is off but if you have a lan cable plugged in, look at the back of the pc, even powered off those lan lights are on, and the motherboard is constantly looking for a signal to turn on - FROM THE LAN.
There are many such systems integrated into the new designs. WOM (wake on modem), WOK (wake on keypress), WMC (wake on mouse click) and so on... It's funny to me that people who have mouses that have lights in them that are usb powered are always saying "how come my mouse stays lit up even when the pc is off?" - then I have to explain why.
There is a whole group of circuit logic systems allocated to this! It even includes the southbridge (wake on usb keyboard, wake at a certain time of day and date, wake on a request from the pci bus, even wake on super i/o notifications such as a ring on the serial port (wake on modem) and the ps/2 ports too!!!
So anyway, we came a long long way since the old days, when the 120 or 240 volts was turned on and off to the psu. Now the psu's special low power always on subsystem command monitoring bus is always running and tightly integrated into nearly every aspect of the computer itself.
Pin 9 on your motherboards power supply main cable is the +5 VSB (5 volt standby). Push the button, and it momentarily closes (or opens) a circuit which causes the power controller chip on the motherboard to go "o yay we got a signal to do something."
Some motherboards try to remember if the system is on or off by saving some little data somewhere in a volatile ram on this power controller chip that way when they get the button press they know whether to:
1.) turn on the pc if it's actually off.
2.) turn off the pc if it's actually on.
3.) if the signal continues for a long period, clear the memory of the power controller chip and reset the psu status.
so for example, if you quickly press and release the button, if the pc is off, then the pwc sends a signal to pin 16 on the motherboard connecter ( the green wire ) which is called Power Supply On, as you would suspect, this turns on the psu.
Now, please do not be confused. The PSU ALWAYS has that other tiny trickle power running to all those different systems on the computer, the network card, the modem, the keyboard, the mouse, usb, etc. etc. I guess a better way to say this would be to just say "This turns on the 'big' power which brings up the system.".
When the computer is running in full operation there is a 5 volt signal (positive with respect to chassis ground) on the pwr_good line and that is the gray wire pin number 8 of the motherboard connector.
Now for the easy fun stuff... Every motherboard maker felt free to design these new power circuits anyway they pleased, there's no standard that I am aware of... Some simply use a simple pnp junction field effect transistor as an interface to a motherboard power connector pin, since the logic is the same it works by allowing the transistor to directly drive the signal.
Other mother board manufacturers use custom power chips that have pins going out of them all over the motherboard to provide a tiny computer that controls the entire psu "rise and shine" function.
So... Is it any wonder that if the little microcontroller which is supposed to remember if the pc is already on or not (maybe your configuration actually stores a bit in the escd to indicate the current status?), if that got confused - whether in ram or live in the microcontroller itself (which is always on and being powered even when the pc or laptop is shutdown), that option 3.) push & hold might be necessary? Sometimes, even the little microcontroller is so confused you have to remove all power to the thing so it can allow everything to reset.
You can also use the other method of unplugging it and waiting a few months for all the caps to completely drain. (LOL). That's definitely another technique.
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