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Title: DSO5202P noise CH2 [Print this page]

Author: serge73 Time: 2017-10-30 19:53
Title: DSO5202P noise CH2
Edited by serge73 at 2017-10-31 11:28

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

[attach]1749[/attach][attach]1754[/attach]
20mV without probe

[attach]1750[/attach][attach]1753[/attach]
2V without probe

[attach]1751[/attach][attach]1752[/attach]
5V without probe

Author: amy Time: 2017-10-31 17:04
Sir, in other gears, are there the noise? Or only 20mV and 5V have the niose?

Author: serge73 Time: 2017-11-1 14:03
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:
[attach]1755[/attach] [attach]1756[/attach]
[attach]1757[/attach][attach]1758[/attach]
[attach]1759[/attach][attach]1760[/attach]
[attach]1761[/attach][attach]1762[/attach]
[attach]1763[/attach][attach]1764[/attach]
[attach]1765[/attach][attach]1766[/attach]
[attach]1767[/attach]

Author: amy Time: 2017-11-1 14:54
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.

[attach]1768[/attach]

Author: serge73 Time: 2017-11-8 02:43
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
[attach]1772[/attach][attach]1773[/attach]

2. probe ch2 is disconnected.
[attach]1774[/attach][attach]1775[/attach]

Author: amy Time: 2017-11-9 16:20
Sir, which picture is point1 and which picture is point2?

Author: amy Time: 2017-11-9 16:30
Please try to replace the five triodes.
D100： BAV99LT1G
Q100：SST4393-TI-E3 (or MMBF4392LY1G)
Q101：LMBTH10LT1G (or MMBTH10LT1G)
Q102，Q103：BC846B

[attach]1784[/attach]

Author: serge73 Time: 2017-11-14 17:22
Edited by serge73 at 2017-11-14 17:43

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

Author: amy Time: 2017-11-15 08:59

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.

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