Tom,

no disrespect intended, but I'm looking directly at my 2465, and it has five input coupling positions for channels 1 and 2, labeled in order: 1MΩ AC, 1MΩ Gnd, 1MΩ DC, 1MΩ Gnd, and 50Ω DC (with a red border around the 50Ω DC label). It also has, according to the manual, overload protection in 50Ω DC mode, and will revert to 1MΩ Gnd position in such a case. The precise mechanism of the overload protection seems to be more direct in the case of the 2465, which appears to have a thermal sensor that triggers the switch back to 1MΩ input, but the effect is the same.

-- Jeff Dutky