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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?
1The 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 – 2019-05-03T18:14:06.023
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. – None – 2019-05-03T18:24:25.750
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 – 2019-05-03T18:24:38.210
Did you wait five minutes before reseating the battery. – Tony Stewart Sunnyskyguy EE75 – 2019-05-03T18:27:22.780
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. – None – 2019-05-03T18:27:54.650
No I think I waited round about two minutes. You think this was to short? – None – 2019-05-03T18:29:00.567
Make sure you take out the main battery, the bios battery and the power cord – Voltage Spike – 2019-05-03T20:13:12.127
I dont think a relay is a good idea, but I dont see how a relay requiring 7 volts can be driven by 5 volts + transistor. Transistors amplify weak signals but do not boost maximum voltages (you need caps and/or coils for that, possibly using transustors for the required oscillation) – davidgo – 2019-05-03T20:33:51.790