Prepared a new DIN cable to run between the Fox Delta STS-2 USB satellite interface and my Yaesu G-5400B. 

Tinned all wires, and checked them for correct configuration with an ohm meter. 

With USB cable disconnected, I attempted to do the initial calibration. This failed. Immediately, when powering on the G-5400B, the rotor transits to full UP elevation with on control input. 

The STS-2 will control movement from left to right normally, but has no effect on elevation up or down. 

When the DIN cable is disconnected, manual control of the rotor with it’s front panel switches is normal. 

Removing the top panel cover on the STS-2 USB, I can see that LEFT, RIGHT, UP, DOWN LED’s light up as expected when control inputs are pushed. Judging from this, I assume the problem may lie inside the Yaesu G-5400B control box itself. 

Any ideas on next steps for troubleshooting or lacking that, can someone recommend a repair service for the G-5400B control box—even better one that could repair the G-5400B and verify proper operation of the STS-2 (assuming that I ship them both units.) 

Thanks again for all the help. Sorry to consume so much bandwidth on the list.