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PC Power Button Not Working (Start Long Delay)

Does your PC turns on only after some time you press Power Button ON? Mine started to do just that and I was searching for the problem for this behavior.

Sometimes computer seems to start on its own without pressing power button. Like a delayed start. Sometimes it seems to work again fine.

Broken PC power button

Broken PC power button

At first I thought that power button was not working and broken and didn’t make good contact inside. I disassembled it and found that indeed printed circuit board was broken in half (probably when I tried to press it harder when no start condition began).

I replaced it with the new DIY button and it seemed at first the problem was solved, however it reappeared the next day.

Then I realized  that computer only starts with delay first time in the morning when I plug it back in the mains socket. (Yes, call me paranoid, but I disconnect power cord from all equipment every night when I shut down computer.)

Later in the day power button seems to be working with no problems. You can restart the computer how many times you want without a problem. So I thought maybe connector that attaches to the motherboard somehow loses connection and power button can not close the circuit to send starting signal.

PC Power Button Replacement

PC Power Button Replacement

After several days keeping computer open on the table and wiggling power button connector in hope to make a solid connection I decided to go even further and solder 2 wires straight to the motherboard pins.

Power button is quite simple thing. One wire is ground and the other is signal with about 3.3V. When you press the power button it connects two wires and pull 3.3V signal to the ground making it 0V. Computer sees that signal going low and responds with starting up the system.

When I had 2 wires soldered straight to the motherboard then I could eliminate all connection problems because there is no better connection than straight soldering.

Only when I started testing voltages on the 2 wires I found the problem. When you first plug the computer in the mains, signal voltage doesn’t go up to 3.3V instantly. At first it rises to about 2.5V but when you connect it to ground nothing happens. You have to wait for another minute or so when voltage climbs to the proper 3.3Volts.

You can see in the  picture above that I’m running two wires from the PC computer as a replacement for power button that is not working at the moment. And you can see I hooked it to the multimeter which shows the signal voltage of about 3.4V. That is the voltage you have to see in your computer in order to eliminate or prove connection problem. To start the computer you have to touch 2 wires together and this shorts them out. Don’t worry because this is only a signal wire, which means current is very limited to maybe mil-thousands of an amperes.

So now you can see how the whole situation worked. When I connected PC to the mains in the morning and tried to start with power button immediately it wasn’t working because signal voltage was to low. If I left it long enough or didn’t unplug at all maybe I wouldn’t have noticed the problem.

So what does this mean? Probably one of the capacitors in the power supply unit gone bad and doesn’t do its job properly. Bad capacitors often bulge and swell and you need to replace them. However apart from this start delay I have no problems so far and maybe leave it as is for the moment.

Reasons why your computer power button might not be working:

  1. Power button may be broken physically
  2. Bad contacts in button or connection to motherboard
  3. Too low signal voltage meaning failing PSU or motherboard.

I hoped this article helped in some way. You can write comments if you have any questions and I or other readers might offer a solution to your problem.


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