Roy,
One of the two diodes is probably faulty, so it cannot measure a reflected signal.
If you want to fix it, get a 1N63 or 1N60 and measure it for the same opening voltage if you are a maximalist.
The side wall on the side of the BNC connector must be removed and the connecting wires disconnected,
then the two diodes will be easily accessible for soldering.
If you take out the diodes, you can measure them individually.
These are Ge diodes. Don't ask how I know.
--
Gyula HA3HZ
HA3HZ