DSO5202P noise CH2

serge73

Good afternoon!
A year ago I purchased the DSO5202P. Used little. CH2 did not use for measurements. I took the oscilloscope off the shelf, blew out the dust , turned it on, and there's noise on Channel 2. Please help me fix it, it's not very convenient to work, the second channel always turns on after I click on AutoSet.
Return to Aliexpress is not possible.

Can this relay, as in many other malfunctions? On the video there is a moment when the noise disappears when the scan is 2V. At this point, the relay clicks.

Made a video. A copy of the screen with system information. See the link.

https://yadi.sk/d/G3cAAwtu3PDxPq


20mV without probe


2V  without probe


5V without probe

serge73

I'm sorry, I misled you.
Up to 5V the amplitude of the noise is 150mV, starting at 5V the amplitude of the noise is 5V.
At 5V / Div, the relay is clicked.
Note! On CH2, there is no automatic switching of 20Mhz BW to LimitOff.
On CH1, the 20Mhz BW switching is off at 20mV / DIV
Pictures on all modes volts / div:

serge73

While I can not find another oscilloscope.
Using the probe CH1, save waveforms of the two points of CH2.
Maybe this will somehow reveal the problem.
The photographs show a change in the amplitude.
On the second pair of pictures there are no noises.

1. probe ch2 is connected to the built-in generator


2. probe ch2 is disconnected.

serge73

Thank you very much for your help.
I changed only three elements D100, Q102, Q103
The problem is gone. The functionality has been completely restored.

Tested the removed elements, unfortunately, the problem is not revealed.
https://yadi.sk/i/mitiBPXc3PgQ7z
https://yadi.sk/i/wZWwWGO63PgQ87
https://yadi.sk/i/DhXuQX_23PgQ8B