The confusion is understandable. There are so many different variants of
the FE-5680A, and they are not easy to identify.

Some of the information you see out there is from folk who measure the
voltage on the pins with a meter, not understanding what they are
looking at. When I've investigated such devices (I have several FEI
units) I start by tracing my way back from the power supply regulators
to determine where the power goes in, and what it should be, to avoid
mistakes. It's also been a useful technique with things like GPSDOs
where nothing is known about the pinouts (Trimble NTGS-50AA for

Sure is frustrating when you have one that isn't frequency agile! One of
my FEI units is an FE-5680B with only 1pps output. The Chinese supplier
thought it was faulty, but the 1pps pulse is only 5us wide, and isn't
present until the unit has locked. I found a very useful 60MHz reference
inside the unit as well.

Murray ZL1BPU

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