I have a GTN750 and dual G5s, hooked to an STEC-30 AP. On a GPS approach, everything works as expected but today flying an ILS approach, I first tuned the ILS frequency (110.9) in the 750, then selected and activated an ILS approach (16R X at KRNO) and got what looked like a back course ILS arrow but no glide slope. The arrow was green and LOC was selected on the CDI button of the 750. The needle was pointing down and the R/L of course line seemed to be working. On the GNC255 hooked to a mechanical CDI, I got both needles. What Am I doing wrong to get the ILS working right on the G5. It has worked before but I have also run into this before where no glideslope appears.