select data from combobox

hi,please help .currently i have data at combobox as below:
AC28_&_2240

what i want to do now is when i select the value from combobox for example:
AC28_&_2240 then the txtmachineno.text will only display AC28.

please help.thanks.

Code:

---

txtMachineNo.Text = Split(Combo1.Text, "_&_")(0)

---