[Test-Equipment] HP 8640B Counter Not Working Properly

[Barry]

The counter on my generator shows all zeros (both in INTernal mode and EXTernal mode when connected via the front panel BNC jack).  I fed the external time-base (rear BNC jack) to a counter and verified 5Mhz is present there.

My first step will be to verify that a signal is indeed making it to the counter board.  If that is present (and I assume it probably is), then I'll have to investigate the counter board(s).

Is it a valid method to trace out the signal path with a scope?  In other words, I think I should be able to verify there are ECL-level and/or TTL-level signals along the path and at least be able to see if there's a point where the signal stops.  At that point, then I would start looking for bad components, etc.

Is that a viable approach?  I assume that tracing this out with a scope probe won't give me false readings due to loading, etc.  Is that correct?

Thanks,
Barry - N4BUQ