I am having problem with 555 timer. Everything looks nice when channel is put to DC coupling, pic #1.
When I switch to AC coupling (pic #2) on my Rigol scope, I see nasty non-square like waves. I am not sure what's going on. What I don't understand is the falling edge goes to -8.8V. I would expect it to be around -5V when AC coupled, kind of symmetrically distributed from the center 0V point, my PSU is set to single +10V. Why don't I see top and bottom edge flat anymore? Any idea?