This is normally caused by dirty / faulty test leads.
Please check out the reference value stored in the tester. To do this, rotate the dial to Autotest and press F3 to View Ref.
Figure 1. Ref from DSP-FTA440S
The values should be in the following range:
- DSP-FTA 410/20S 62.5/125 µm Multimode Fiber, between -19 dBm and 20.5 dBm 50/125 µm Multimode Fiber, between -23.5 dBm and 24.5 dBm
- DSP-FTA 430S 9/125 µm Singlemode Fiber, between -7.8 dBm and 10 dBm
- DSP-FTA 440S 62.5/125 µm Multimode Fiber, between -8 dBm and 10 dBm 50/125 µm Multimode Fiber, between -8 dBm and 10 dBm
There could also be dirt in the adapter. Using alcohol and a lint free bud wipe, gently clean the inside of the SC adapters.