try this
string query = "select PN,Type from BIn";
SqlCommand cmd = new SqlCommand(query, con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
comboBox1.DisplayMember = "Type";
comboBox1.DataSource = dt;
comboBox2.DisplayMember = "PN";
comboBox2.DataSource = dt;