2. The most frequent cause of problems is simply a bad contact in wiring connectors. So always make sure that connections are secure. When inspecting the connector, pay particular attention to the following points: (a) Check to see that the terminals are not bent. (b) Check to see that the connector is pushed in completely and locked. (c) Check to see that there is no signal change when the connector is slightly tapped or wiggled. 3. Sufficiently troubleshoot for other causes before replacing the computer. The computer is high quality and it is expensive. 4. Use volt/ohmmeter with high-impedance (10 kΩ/V minimum).