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

amy

Sir, in other gears, are there the noise? Or only 20mV and 5V have the niose?

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:

amy

Please disconnect any probes of cables to the CH1 and CH2, use another oscilloscope to compare the waveforms of the two points of CH1 and CH2 in the picture.

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.

amy

Sir, which picture is point1 and which picture is point2?

amy

Please try to replace the five triodes.
D100： BAV99LT1G
Q100：SST4393-TI-E3   (or MMBF4392LY1G)
Q101：LMBTH10LT1G  (or MMBTH10LT1G)
Q102，Q103：BC846B

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

amy

serge73 replied at 2017-11-14 17:22
Thank you very much for your help.
I changed only three elements D100, Q102, Q103
The problem is gon ...

Sorry, I don't know much about the components.