The detector wiring is damaged, especially if the LED’s are still flashing. NOTE: CDOM channels do not have visible LED’s, so, do NOT look into the CDOM LED port to confirm its operation (!!).
The ECO firmware is programmed to output an unchanging “floor” value of output counts, if there is no signal from the detector.
Conversely, if the LED is burned out, one would see a changing serial output count, dithering around the ECO dark count value or showing another ambient light condition/change (i.e. values would be changing 48, 51, 47, 52, etc…).