DSO5072P x1 probe Bug?

[alpuy]

I recently purchased a Hantek DSO5072P oscilloscope and while testing it i found something a bit strange.

When using the probe in x1 and connecting it to the 1 kHz 5V test signal when the amplitude is set to 200 mV/div or less there is a deformation in the bottom cycle of the signal, when the amplitude is greater than 200 mV/div the signal is shown correctly with a bottom cycle of almost 0 V.

In this video at 18:20 the same thing happens to that guy:

The question is: Is it a known bug? Is it a hardware problem? Or is it normal, caused by using the probe at 1x?

Thanks

[Keysight DanielBogdanoff]

If I had to guess, I'd say it's one of two things.

In the video you provided, it's a probe compensation issue. The probe and the scope need to be properly compensated. I talked about that a while back during Scope Month here:
 

First, it's possible that the compensation network changes at 200 mV/div, I'm not sure how this scope's front end circuitry is setup. You could test it with a smaller Vpp signal (signal should stay completely on screen) and see if it changes.

Most likely, you're violating the oscilloscope's dynamic range . With a 5V signal and 200 mV/div setting, you're looking at 25 divisions of signal. That's surely saturating the front end amplifiers and can cause weirdness.

If you want to learn more about front end stuff, check out this talk from one of our designers: https://www.youtube.com/playlist?list=PLzHyxysSubUmxGOMVpiKLxouweh2AAlG1 Feel free to skip video #1 if it looks too basic.

[alpuy]

If I had to guess, I'd say it's one of two things.

In the video you provided, it's a probe compensation issue. The probe and the scope need to be properly compensated. I talked about that a while back during Scope Month here:
 

First, it's possible that the compensation network changes at 200 mV/div, I'm not sure how this scope's front end circuitry is setup. You could test it with a smaller Vpp signal (signal should stay completely on screen) and see if it changes.

Most likely, you're violating the oscilloscope's dynamic range . With a 5V signal and 200 mV/div setting, you're looking at 25 divisions of signal. That's surely saturating the front end amplifiers and can cause weirdness.

If you want to learn more about front end stuff, check out this talk from one of our designers: https://www.youtube.com/playlist?list=PLzHyxysSubUmxGOMVpiKLxouweh2AAlG1 Feel free to skip video #1 if it looks too basic.

I will try with a smaller signal to check if the front end circuit is saturating, what is strange is that the signal is already small where it is distorted (indeed it should be 0 V) do you think that the previous half of the period in 5 V could be afecting the second half of the period?

Also i forgot to mention that with the oscilloscope set to 200 mV/div and the probe at 1x, if i change the probe switch to 10x the distortion goes and the signal goes to 0V.

I will post again when i test what you said.

[alpuy]

I now have a ds1054z rigol oscilloscope and the same problem occurs with 1x probe and 200 mv/div or less.

So, anyone else knows why this happens?

If it is normal, how can someone see small voltages in signals which have large voltages at times and with 1x probe?