Kit 6002; temperature controller

Just completed kit K6002 - temperature controller - which not working correctly. Controller shows ‘FAIL’ on power up, as it should, but then fails to respond to ‘Select’ commands after connecting temperature sensor K6001. 1) schematic for K6002 shows C7 connected, capacitator also supplied in kit, despite which instructions say ‘Do not mount!!!’ ? 2) K6001 manual says use 12v unregulated power supply, then shows in fig.1.5 9v supply ? 3) The only test suggested for the controller is correct function after connecting the temperature sensor. Would appreciate any suggestions re. further troubleshooting. 4) Hardwiring the connections between the three boards may be space-saving but makes any investigation of problems very difficult. Thank you.

Do not mount C7
9-12VDC is fine for sensor K6001.
Make sure to feed K6002 with an AC supply.
Check if signal from K6001 arrives at the opto-coupler input of K6002.

Thank you for the advice. Have used the power voltages suggested, re-calibrated the K6001 sensor to 0oC, but the controller will still only display the ‘FAIL’ message. The input to the controller’s opto-coupler is approximately 0.3v at 20oC. Next?

Check (with an o-scope) if you get a square wave at the output of the K6001.
If this is not the case, check K6001 assembly.