If a generation 1 equipment is acting erratic (unable to tune properly, no responding to buttons, switching valves, acting randomly) there's a possibility that the power supply for the card rack and the 90/900 boards is dropping below the required threshold.
-Measure wires 505 (+5V), 512 (+12V) and 513 (-12V) at the 90/900 board, while the machine is running or acting erratic. Ensure that the +5 volt supply is minimum 5.2 volts. Adjust power supply if required.
-Measure the supply voltage at the card rack to ensure the same 5.2 volts are present while machine is running or acting erratic.