I found the problem with my Drake R7 with blank display. First of all, the
display board does have other problems. I ordered a new DR7 board from that
Charlie fellow on the east coast, and when I installed it the display was
still blank.
Now, there are two signals that come from the VCO board. One of them is the
1st LO signal; a frequency counter confirmed that the system does lock, in
addition to being able to receive signals in the first place.
Here is where the plot thickens................there is another 3-pin Molex
connector that mates with the DR7 board. This provides the 500kHz gating
signal for the frequency counter portion of the circuit. This signal
originates on the Translator board and is connected through the motherboard
to the VCO board. This signal splits into two paths; one path is applied to
the reference port of a 4046 phase detector while the other path is applied
to that 3-pin Molex connector on the top of the VCO board. Since the PLL
does lock up properly, we know that the 500kHz signal is present on the VCO
board itself and it is getting to the input of the phase detector.
I didn't see this signal on Pin2 of the Molex connector so I applied a
500kHz square wave signal to the input of the 4017 divider chip that is
supposed to be getting that signal. When the display started working, I
realized that I had a broken connection on the VCO board.
Close inspection under a stereo microscope revealed that the contact in the
3-pin Molex connector had become unsprung.
When I received this unit, the connector was mounted crooked so I removed
the solder from the pin connections and reseated the connector. Now, if I
can either re-center that spring contact or find a new connector, I will be
in business!

Pete