RE: DX7 Crashed Two Planes
You say that you checked the rx voltage and it read 4.8 volts. I'll assume you are using a 4 cell Nimh or Nicad and if that's the case, then that would be the nominal voltage not the fully charged voltage in which case, that isn't good and may very well have lead to your results. It was simply too low of a voltage for your rx.
If it were me, I would start with at least a 6 volt battery system on the rx. Spectrum, in my opinion should not be run with a 4.8 system as that will lead to a typical brown out, especially if you started out with a 4.8 battery that may not have been fully charged.
Try using a higher voltage battery. Just my thoughts.