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I'm not pro with electronics and electricity and I want to replace my notebook socket so I'm looking for a coaxial jack dc socket but, as I only have two cables (a positive and a negative one) to solder to the socket, I can't see the purpose of a third solder terminal.

Is it for the grounding or something like that ? Can I use such a socket without using the third terminal ? (If that's the case, which one am I supposed not to use ?).

I know that I could directly buy one with two terminals but that's not the question.

http://i.imgur.com/aNqo4tj.png (two terminals)

http://i.imgur.com/U1PUqAM.png (three terminals)

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  • \$\begingroup\$ How do you intend to remove the 'damaged' one? Unless you have good tools and experience, I wouldn't go hacking up and melting my laptop's motherboard.. \$\endgroup\$
    – KyranF
    Nov 23, 2014 at 20:20
  • \$\begingroup\$ That's not a problem. The old jack isn't soldered to the motherboard but to two cables so I just have to solder those two cables to the new jack, which doesn't seem too complicated. \$\endgroup\$
    – Desura
    Nov 23, 2014 at 20:59
  • \$\begingroup\$ that's strange, but okay \$\endgroup\$
    – KyranF
    Nov 23, 2014 at 21:04
  • \$\begingroup\$ So the manufacturer is strange ? Just kidding. It does look like that : insidemylaptop.com/images/Toshiba-Satellite-L305-L355-power/… \$\endgroup\$
    – Desura
    Nov 23, 2014 at 21:07
  • \$\begingroup\$ Right so instead of PCB mount, they went for panel mount and some wires? Seems silly, and on a Toshiba Satellite which are low cost, i'd have thought they would reduce manufacturing by making it as single-board as possible (with less assembly steps like panel mount sockets) \$\endgroup\$
    – KyranF
    Nov 23, 2014 at 21:12

2 Answers 2

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The third terminal is like a switch. When you have nothing plugged in the third terminal is connected to one of the others. When you plug something in the third terminal is disconnected.

It's primarily designed for automatically switching between battery and external power.

The schematic symbol is:

enter image description here

With nothing plugged in pin 2 is connected to pin 1. When you plug something in it pushes against pin 1 separating it from pin 2.

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  • \$\begingroup\$ So is it okay to leave the third terminal unconnected ? \$\endgroup\$
    – Desura
    Nov 23, 2014 at 21:19
  • \$\begingroup\$ Yep. You can just ignore it. \$\endgroup\$
    – Majenko
    Nov 23, 2014 at 21:20
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My guess is that the extra terminal on the three terminal jack is to indicate when a plug was inserted. These are usually normally closed and open once a jack is inserted. I usually tie these to GND. Test my theory with a multimeter by measuring resistance with and without a jack inserted.

I agree with the above comment that this is not a trivial rework if you have no experience, so be careful. Would be a shame to ruin a laptop.

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