[Test-Equipment] Question Regarding HP8640B Counter

[Barry]

The counter in my HP8640B is not working correctly.  I've verified all the normal things (e.g. switch on back in correct position, time-base is working, cleaned switches, tested with EXT input, etc.) and I'm down to board-level tracing.

The signal being tested enters the counter at the scaler and feeds a comparator.  I've not opened the lid on the scaler yet, but if I look at the signal coming out of the scaler (at U3B), I get a sine wave that varies from about 1V p-p to 2V p-p (depending on the position of the frequency knob).

Is this normal?  Wouldn't the comparator have made that incoming sine-wave into a digital signal which would be carried on through the other gates as a digital signal?  I can't figure how the output from a properly-functioning NOR is anything but a digital signal.

Am I missing something here or is there some way an analog signal is supposed to make it through the gates like that?  Sorry if this sounds like a dumb question but I'm not seeing at all what I thought I'd see at that point and am quite puzzled.

Thanks,
Barry - N4BUQ