Possible problem with my EDU06 board?

Hi. I have the EDU06 Oscilloscope Tutor Kit, and I never got good clean results from it. Signal traces on my scope (RIGOL DS2072A) were not clean and neat as I would expect. I wrote the issue off as likely being caused by a poor AC power signal from the wall wart I was using.

However, I now have a nice workstation that incorporates a good quality Function Generator. I can adjust it to output a clean 60-Hertz signal, and the scope shows a perfect sine wave trace. But when I connect the EDU06 board, with SW1 in the top position (single phase mode) the top half of the signal (positive voltage) is clipped significantly. When I move the switch to the bottom position (dual phase), the signal appears clipped on both the top and bottom (positive and negative voltages).

Is it possible there is a bad component on the board? Maybe a bad diode?

Thanks for any insight you can provide.

~ Russ

This is normal behaviour due to limitations of the small transformer used in low-cost wall-warts.