Power adapter center pin

[bazofstour]

I have a compaq nx6325 lap top, which will not turn on at all. The power adapter
shows 18V between the inner and outer ring and appears ok, led on etc.But what's the tiny center connector for in the plug? Should there be a voltage on it to earth, or to the ring connectors?Finally,should I be able to power-up the lap-top with the power adapter plugged in, and the battery out?

 

[ucould2]

Sounds like the Centre pin has broken away and lodged itself in the plug. I cannot tell you which is positive and which is negative with regards to the rings on the plug. Because different Manufacturers use different combinations and with that different Voltages too. Generally speaking the outside piece is the male end and the receiving plug is the female -go figure-
Hope this link works http://www.niteflux.com/BuyCables.aspx you can see what I am mentioning, obviously this is not your cable but for the example of male to female ends the description matches the pictures ( not the 'Y' cord on the link )

 

[bazofstour]

Many thanks! I've found the problem to be the wire that feeds the center pin to be broken from its termination in the plug. This requires cutting half the plastic compound of the plug away to reterminate, but I did it successfully and rebound and taped it up to be mechanically strong.I hate wasteing money! The configuration of power lead found to be:-
Outer Ring- earth or 0V white wire
Inner Ring- +18.5V Red wire
Center Pin- about +7V Black wire

The center pin must be part of the power management system,as the computer won't power up without it, but can find no info about that.