I've a Rigol DS2072A. It works great except for an offset problem that I noticed the past few days.
Channel 2 always shows a DC offset. This is independent of any settings such as channel coupling, internal termination resistance or bandwidth limiting. The input connector only has a 50 Ohm terminator connected.
It's a constant height above 'zero' on the screen, independent of vertical scale. This means that for higher ranges, the scope calculates that there is more offset. (e.g. 80mV@1V/div vs. 8V@100V/div).
I noticed that the offset lowers when the scope warms up.
Only for the lowest scales (in the millivolts range) the offset changes with the scale setting, but there is no sound of relays for these scales, so it's probably software scaling what we're looking at in these regions.
I attached a picture where you can clearly see the offset:
Running any calibration commands doesn't change anything.
Is there a way I can fix this? Or does this indicate that the scope is broken?
Is this a case of 'you get what you pay for' or just bad luck?