The outputs (Q0-Q3) of the memory are always LOW. The address lines (A0-A7) are checked with a logic probe and all are indicating pulse activity, except for A3 which shows a constant HIGH, and A7 which shows a constant LOW; the select lines, S0 and S1 are checked and S0 shows pulse activity, while S1 indicates a constant HIGH. What is wrong, and how can the memory be tested to determine whether it is defective or if the external circuitry is defective