If the OTDR you bought is with 2 wavelengths, but only one works in good condition, the other one does not work, it is laser problem. See the picture (1550nm laser is with problem). You have to contact our technical service team to repair it.

Model 8000MAX OTDR Laser Problem
Model 8000MAX OTDR Laser Problem
Model 8000MAX OTDR Laser Problem
Model 8000MAX OTDR Laser Problem

if both two wavelengths do not work, it should be just not plug cable connector into OTDR in right way, or cable is too short.