I had a niggling issue with the Owon VDS10022 that caused me a bit of an problemuntil I figured out what was causing it.
The problem was I suddenly started having issues measuring DC signals, the scope worked fine on AC -- and it would show the scopes built in 5v 1kHz test square wave without issue on both AC and DC settings. At first I blamed bad test leads then a bad attenuator but the issue was much simpler.
Owon in there wisdom to cut assembly cost to the bone used plastic BNC connectors and these were not giving an intermittent ground connecetion. The quick fix was to very gently squeeze in the outer sleeze of plastic outer shell of the connector on the oscilloscope. Only a fraction of a mm is required just enough so the contact friction can be felt when connecting and disconecting test leads.
I am working on a more puka fix but this is the immediate work around.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I have found the same thing when using the generic attenuator with the Owon.
I will give that a try next time.
Let me know if you find a different solution.