Sign in with
Sign up | Sign in
Your question

What is sequence from pushing the power button to startup PC

Last response: in Components
Share
Anonymous
a b ) Power supply
a b V Motherboard
January 17, 2010 10:46:35 PM

The power on momentary switch is connected to the motherboard. What does the signal go through to finally connect the to the ATX pwr_on line to fire up the power supply. Evidently, there is some other logic between the power on button and the ATX.

My problem is: If I clear the cmos and jumper the pwr on line to ground, then the system fires up, loads windows XP and all is fine. The power switch is good and connected to the motherboard correctly. I then remove the jumper to shut down the PC, then I removed the power cord.

After removing the jumper, I inserted the power cord. The front panel switch activates but nothing happens. The processor and system fans are not running. No action and system is just dead.

Brand new mother board. ATX power supply checked out under load OK.

Any Ideas?
a b ) Power supply
a c 216 V Motherboard
January 18, 2010 12:46:19 AM

Quote:
I then remove the jumper to shut down the PC, then I removed the power cord.
What do you mean? Does the PC shutdown as soon as you remove the jumper or when you disconnect the power cord? Using a jumper, the PC should power up as soon as you put the jumper on and remove it. Same with the power switch. There could also be a 4 seconds delay to power off if it's configured that way, i.e., you need to keep the jumper on or press the power switch for at least 4 seconds.
a c 144 ) Power supply
a c 156 V Motherboard
January 18, 2010 1:57:25 AM

When you press the case power switch, it applies a ground to the green wire through the motherboard (same as the paperclip trick). That's one reason that you need the always on standby power supply. It powers the PSU circuits that then kickstart the PSU and activate the main power circuits. As soon as they all reach operating voltage, the "PowerOK" line (gray wire) goes to a Logic HIGH (5 volts). This removes the hardware reset from the CPU and the system boots.

If you hold the case power switch in for 3 or 4 secounds, the PSU is supposed to shut down.

So first thing, to test the case power switch, swap it with reset switch and try to boot with the reset switch.

Now, when you tested the PSU in the other computer, I bet you didn't try to power down by holding the case power switch in (safest way to test this is to boot and enter the BIOS).

Please post system specs.
Related resources
a b ) Power supply
a b V Motherboard
January 19, 2010 3:18:08 AM

I am confused by your story. The two mobo pins that are connected to the front panel power pushbutton are supposed to connect to a MOMENTARY-contact switch. When the system of off, a short-term "short" across these pins initiates the start-up and, after it gets power going, its function changes. For a computer that is already running, a short-term connection between these pins is normally ignored by the BIOS. But a long (typically, >4 seconds) "short" initiates a shut down sequence.

You SAY what you did was disconnect the front panel leads and place a short jumper on the pins, so it started up. No surprise. BUT once it had full power, the jumper was still there? For how long? Why did it not detect that as a "short" of the terminals over 4 seconds and cause a shut-down? Then you say that you shut down the PC by removing the jumper? Or, by removing the power cord?

You tell us that when you connect the front panel push switch leads to the correct mobo pins and plug in the power cord, the system will not respond to a push of that switch. And yet you tell us the switch is good?

Like they used to say, "Does not compute!"
Anonymous
a b ) Power supply
a b V Motherboard
January 19, 2010 8:31:31 PM

Quote:
The power on momentary switch is connected to the motherboard. What does the signal go through to finally connect the to the ATX pwr_on line to fire up the power supply. Evidently, there is some other logic between the power on button and the ATX.

My problem is: If I clear the cmos and jumper the pwr on line to ground, then the system fires up, loads windows XP and all is fine. The power switch is good and connected to the motherboard correctly. I then remove the jumper to shut down the PC, then I removed the power cord.

After removing the jumper, I inserted the power cord. The front panel switch activates but nothing happens. The processor and system fans are not running. No action and system is just dead.

Brand new mother board. ATX power supply checked out under load OK.

Any Ideas?


Thanks for all your responses. I found a bad IC in the Hipro ATX on the pwr on line. Replaced from another Hipro supply solved the problem.
a b ) Power supply
a c 216 V Motherboard
January 19, 2010 8:58:08 PM

That explains the weird behaviour of your system.
!