An old notebook I found in the basement always tries to boot from the network as I start it. Unfortunately I've forgotten the BIOS password.

I figured out that one USB port delivers power until Windows has booted. My idea was to cut the Ethernet connection with the power of this USB port. As I read I just have to cut the wire of pin 6 with a relay.

As all of the relays I have laying around need 7 V to work, I wonder if I could use a transistor as well, but as I am not too familiar with transistors, I am not sure how to do this.

Can anybody help me?

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  • 1
    The problem with doing this is ethernet is impedance controlled, so running it through a relay will change the impedance and cause noise and packet loss. A better way would be to take off the bottom cover of the laptop, find the bios battery and unplug it for 30 seconds to reset the bios – Voltage Spike May 3 at 18:14
  • I already tried to put out the bios battery but it didn't worked. I read this trick is not working on some devices maybe it's like this here. – Maximilian May 3 at 18:24
  • I take it that you're trying to avoid the long delay while the laptop times out waiting for a nonexistent network boot server. Why can't you just wait to plug in the Ethernet cable until after Windows has booted from the local drive? – Dave Tweed May 3 at 18:24
  • Did you wait five minutes before reseating the battery. – Sunnyskyguy EE75 May 3 at 18:27
  • That is how I am doing it right now but I am using a dockinstation, and a separated monitor so I always have to put the laptop out of the dockingstation, start it and put it back in. This is not a really elegant way. – Maximilian May 3 at 18:27

If you really want to experiment with this USB powered relay idea you can get 5V relays, or USB cables that emit 12V such as this

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