I'm using a Tektronix TDS3034 4-channel oscilloscope to check a board. All channels are using P6139A 10x probes. It's triggered off channel 3, which shows a fairly clean square wave, swinging between 0V and 3.3V. Horizontal is holding steady with only a rare glitch causing some jitter. Everything looks fine so far.
Except when I use the built-in frequency measurement, I get a plausible reading, but along with the text "low signal amplitude" on the screen. If it's physically receiving 0.33 V at its input, shouldn't that be fine?