I've just done one and stupidly put one battery the wrong way round.
Previously I found a fault in the bell button/push on the door/door frame outside they get rusty and isolate the current so the bell stays silent. remove the push and clean the terminals. It doesn't matter which way round the wires go if they come off unless one has a tracer wire [another thin colour in the sheathing to indicate positive side] So to be safe and you have a digi camera take a picture of the inside you can't go wrong then with re-assembly. Other than that the coil widing has broken down so the electro magnet doesn't work through age. Then it's another bell unit,
charlie, January 2009
