[time-nuts] 5065A Rb Cavity RX - Varactor repair?

[ed breya]

I doubt that the SRD is the problem. It's just the last thing in the 
chain, and a number of things ahead of it all have to work right first.

I'd look first at any connections and wiring between various sections, 
and jiggle things around to see if the symptoms can return. Next, if ICs 
and transistors and other parts are in sockets, jiggle them too. For 
ICs, it's easy to pry one end out slightly - with power off - then press 
it back in, and repeat at the other end if it seems necessary. Re-wiping 
the contacts can do wonders sometimes. I don't know if HP ever used the 
notorious TI IC sockets, but they are a big cause of problems in Tek 
gear. The same for TI brand ICs that have silver plated leads - whether 
socketed or soldered in, these can suffer connection failure. This is 
well known and discussed a lot over the years.

Sometimes an intermittent can be a short instead of an open, with 
various causes, like errant braid strands on coax, wire clippings, 
solder gobs, and loose hardware that happen to eventually land in just 
the right spot. I have found this generally the second most likely 
fault, after open or poor connections. This is also a type that can 
happen once, if say a loose item caused the problem, then gets knocked 
out of place (sometimes to a different place where it can cause a 
different problem later) by moving the unit or opening it up.

The problem in diagnosing an intermittent that came and went only once, 
is that you'll never know for sure what caused it, unless it can be 
forced to fail again and stay that way for a while, and tracked down. 
Or, if you happen to find something rattling around inside that can be 
blamed. Short of that, the next best thing is to check and clean up 
anything suspicious, and hope that you hit the actual culprit in the 
process.

Ed