Problem with waveform generator

I have purchased a DS203 V2.6 about 1 month ago.
I am experiencing some problems with the waveform generator.
It correctly outputs a square waveform at any frequency 1Vpp (is this the correct output voltage? did not find a specification).
But when trying to set any other waveform, all I get is a square waveform with some modifications at the top part which vaguely reminds of a sine or sawtooth or triangular waveform but has nothing to do with any of them.
I had this problem since the beginning and first suspected a firmware bug; but update to 2.50 did not solve the problem.
Then I looked in the manual (0.92b) and saw there a very nice 2Vpp sine wave, which is 2 times the voltage I get from my waveform generator.
Is there any adjustement I should do or it’s definitely a hardware problem?
I’ve attached to this mail an example of “sine” waveform that I obtain (zipped bmp file).
Thank you very much for any information.
Florin Gherendi (4.29 KB)

Ok, I found a similar topic of someone who accidentally broke the waveform generator and the waveforms he had were similar to mine. So I supposed there must be a hardware problem and looked inside my Quad.
Unfortunately in my case the problem was not the double zener D6, but the op amp U7. The signal on pin 3 is correct but on pin 1 I got the same problem even after unsoldering D6.
So I am not so lucky. My Quad being bought on eBay, I guess I’m gonna live with it.

the output should be about2.6~2.8 Vpp

Thank you. I finally found the problem so I ordered and I am about to change the op amp.