[Test-Equipment] HP5328A Counter - Where does the Blue Wire go?

[Eric Lemmon]

I moved the Channel C (512 MHz input) card from one HP5328A counter to
another.  A blue wire from the Channel C card plugged onto an unmarked
pin on the rear of the function selector circuit board in the "from"
counter.  There is no such pin at that location in the "to" counter,
which is a later version of the same model.  However, there are  two
pins in the "to" counter, right alongside the Channel C sockets, one
labeled "C" and one labeled "Not C" (that is, a "C" with a "not" bar
above it.).  These pins do not exist on the motherboard of the "from"
counter.

Curiously, the Channel C input seems to work just fine without the blue
wire connected, but I did not test all of the other functions of this
counter, some of which involve Channel C.  On a hunch, I plugged the
blue wire onto the "C" pin, but noted no change in operation.  That's
where I left it.  My guess is that the "not C" pin might be used with
the Option 031 Channel C module, which goes up to 1.3 GHz.  My Channel C
module is Option 030, rated up to 512 MHz.

I have the basic HP5328A service manual, but not the manual for the
Option 030 Channel C.  Can anyone shed some light on the purpose and
proper connection of the blue wire?

73, Eric Lemmon WB6FLY