Scanning encoder debounce on new scope

[Demon]

SOLVED: Had probes set on AC coupling instead of DC coupling. D'OH!


I am scanning an EC11 rotary encoder wired according to Bourns debounce design using a Owon SDS1104 scope:

R1 = 10K
R2 = 10K
C = 0.1uF (Bourns uses 0.01uF)

https://www.bourns.com/docs/technica...rsn=348415eb_4


This is what the scan looks like:




The peak voltage slowly drifts up as I turn the encoder, and then settles back down. That is not the problem.

I'm concerned with the low voltage, it's also drifting up, well above the 0.8V threshold that is often referred to in Microchip documentation as the LOW level. The 10 or so encoder signals on the right would not get picked up.

Is this normal with RC circuits?

Or is the graph on this $250 DSO drifting north because it's low quality?