Hi
Posted as a bit of documentation if this fault occurs to another Agilent 53230 frequency Counter owner.
Channel 1 was becoming 'intermittent' and the fault seemed to be related to position of the BNC connector/cable, with no force applied no signal was registered, when a little pressure toward the machine was applied to the male BNC, the signal was acquired. Multiple cables would demonstrate exactly the same intermittent fault, and none of these cables would demonstrate this issue with other known good equipment.
A look at the PCB (with the case off and from below) did not reveal any visible faults and the signal could not be found beyond the centre connector.
Reworking the joint (desoldering and resoldering using lead based solder) only served to stop any signal getting through at all!
Tracing the signal in CH2 finds the centre signal goes to an unused (thanks Agilent) resistor PCB pad.
A quick bypass from the centre pin to the PCB pad (as show in photo below) has it working again.
Hope this is a one-off issue.
Ch1 on left side of photo below.