I am looking for the Rohde & Schwarz NRV-Z51 service manual.

[cmu2017]

I have a Rohde & Schwarz NRV-Z51 Thermal Power Sensor which no longer works. It continuously displays -30mW whatever signal I connect to the sensor. And if I zero it I get the message “ERROR ZERO”. I have already searched the internet for a service manual or any information about it to see if I can repair it. But I can't find anything :-(