We recommend that you separate the QSP-2300 from the CTD and investigate the systems separately.
1) Confirm that there have been no changes to the QSP-2300 sensor and the CTD configuration since they were last used together successfully. If there have been changes, then return to the last known good configuration of the system and retest the QSP.
2) Assuming step 1 above did not resolve any issues, measure the power provided to the QSP-2300 sensor by the CTD with the QSP-2300 sensor disconnected. It should be between 6 and 15 VDC. If this is not the case, then I suspect a problem with the CTD, and the manufacturer should be contacted.
3) If power is available for the QSP-2300, then you should be able to verify if the QSP-2300 is functioning properly independent of the CTD. With the QSP-2300 disconnected from the CTD, power it with a fresh 9 V battery (or other power supply capable of 6–15 VDC @ 100 mA) on pins 1-GND and 4-PWR, and then measure the output of the sensor with a digital voltmeter between pins 2-Signal and 3-Signal GND. If there is no response to light at this point, then I suspect something is wrong with the sensor and it should be returned for evaluation. We will issue you an RMA for this to refer to when shipping. If the sensor is responding reasonably, then I suspect a problem with the CTD, and the manufacturer should be contacted. FYI, the sensor should output between 150 and 200 mV when dark, and between 3.5 and 4 V when in sunlight.