Greets,

I've been away for more than a year and have not turned my scope (OWON PDS 5022S) on for that long.
Now there is a problem. The 0v level is a bit lower than the middle of the screen when the Volts per division is set to 2V or higher, but it's ok if it's set to 1VpDivision or lower. Both channels are affected. I've attached pictures of a 1KHZ 5V square wave generated by the scope itself.
Any ideas as to what might be going on?

thanks!

 

Presumably some component common to the two Y-amps (assuming there are two, rather than a multiplexed amp) has drifted in value.

 

Does the zero position change when you switch ranges with no input?
If not, then the generated square-wave may have a small offset or it's a function of the top of the waveform being off scale.

 

hi, again, I totally forgot about the self calibration function. Problem solved