Thank you David Templeton, Harvey White and Mark Vincent for responding to my 465B troubleshooting request. During my subsequent troubleshooting I found that, with the AC-GND-DC Switch set to DC, the gate of the channel 2 input FET was sitting at ~0.5Vdc. Per the service manual that point should be at 0V under those conditions. All the associated components of the input circuitry checked out good so I swapped the dual FETs, Tek P/N 151-1090-00, between channels 1 and 2. That resulted in all the malfunction symptoms (Dead channel and vertical position interaction) also swapping channels.
I now have a replacement 151-1090-00 on order from Qservice Electronics.
Cheers,
Tom
Tom Phillips