Creating Ticker That Show Message As Typewriter?

I'm trying to make a ticker that should show my message as a "typewriter". But it behaves very strange... see attached swf. I have never worked with Flash/actionscript before, so it might be something very simple

This is my code:
var n:Number=0;
var txt:String = "testing ticker";
var len:Number = txt.length;
function tick(){
if(n<len){
txt_bussgods.appendText(txt.charAt(n)); n++;
setTimeout(tick, 1000);
}else{
stop();
}}tick();