Hantek DSo2D15 Woes. Odd wave at low frequencies

[Jwillis]

First off i would like to say that my expectations were really low at the time of purchase. but it was the only thing i could afford.
There are a few problems I've been having like USB not functional and intermediate noise and coupling issues but I will start with the most unusual consistent issue.
 I was taking reading of the output of a astable multi-vibrator  for something to do, and noticed a skewing of the wave that just didn't look right. It should be a square wave. I confirmed it with my analog scope that it was indeed out putting a square wave. 
I did some experimenting to see what the problem is . A really bad skewing of the trailing edge of a square wave at low frequencies. It's starts to be noticeable at around 150 Hz and worsens the low the frequency gets.  This only happens in AC coupling on both channels, 1 and 2 . DC coupling give a square wave without any skewing.
I can simulate the same condition on my analog scope by putting a coupling capacitor lower than 0.01uF between probe and DUT. Lower the value of the cap the more pronounced the skewing.
This kind of leads me to believe that the AC coupling capacitor inside the Hantek is too low a value. I have not checked the actual value as yet.  I believe it to be C109 in the schematic.
Anyone have any thoughts or having a similar problem with their Hantek DSO 2000 series scope?

I've included the schematic to show possible problem. Sorry about the pics. USB seems to have kicked the bucket so I can't give screen shots.

Edited: to low of value to to high of value. Ah geez!I had it right the first time.

[m k]

Test it.
Bypass it like DC would do,
put few known values parallel to it.

It's a derivator so with known values you can calculate how it should behave.
Unknown value will affect but you can also calculate its rationality and then verify if removed.