Encoder issues. RGDС1860.

Hello,
Model RGDC 1860. An error occurs when connecting an incremental sensor to the Sense connector.I have two models, and two have such a malfunction.
With an oscilloscope, I'm observing the ENC3A/B signal doesn't produce a 0 to +5v voltage swing, but rather a 0 to 1.5v swing.
( ENC3A 0 to +5V and ENC3B 0 to 1.5V ).
The ENC2A/B (ENC1A/B) signals are producing the correct 0 to +5v voltage swing on the 25 pin D-Sub connector.
It is extremely inconvenient in our application to use a 25pin connector to connect the encoder.

Thanks,