[ltp] Auxilliary external batteries

[Richard Neill]

Theodore Ts'o wrote:
> I haven't had time to to attempt the repair.  I still need to figure
> out why the power connector apparently has three contacts which it is
> soldered to on the circuit board.  I was only expecting two contacts,
> and so I need to do some experiments to figure out what the third
> solder joint between the connector and the circuit board is all about.

Many power sockets have 3 connections - the 3rd is a switch. Normally, 
that is used such that:

Application		Plug is Out		Plug is In

portable radio - psu    Runs on batteries	Batteries disconnected.
                                                 Runs on mains.

radio - headphones      Internal speaker 	Int. spkr disconnected.
                                                 Amplifier -> headphones



Sometimes, eg in a very small portable radio, the headphone socket acts 
as the power switch  - the battery is connected only when headphones are 
plugged in.

Your connector may be used for something similar, or it may be simply 
for mechanical stability to fix the socket to the board.

(Warning: when you're testing, please be careful not to short circuit 
the battery - you could easily melt a screwdriver on these things.
A single AA 'pencell' NiCad can easily give 50 Amps for a short time!)

Good luck

Richard