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My scope scan mode is broken, can it be fixed? SDS1102CNL
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hlj.pycad:
It works totally fine from 2.5ns/div to 50ms/div timebase in which it runs in trigger mode.

When the timebase is above 50ms/Div, says 100ms/Div, scan mode kick in. The scope captured many nonsense points make the scan mode useless... Selfcalibration pass fine.


It's 1K Hz square wave captured in 100ms/Div timebase, then zoom-in, you can see only a small portion of the zoom in captured waveform show what it is, most of the the data were non-sense dots.
Which parts of my scope is possible broken? And can it be fixed?
ataradov:
This scope has 40 kpts of memory, there is no way it can save high frequency the data as long time scales, the sampling rate will have to drop.

This is not a bug, just a limitation of the instrument you need to deal with, or get one with more sample memory.
hlj.pycad:
thanks for you reply. One thing I don't understand is, 50ms/div should be 200% sample rate compare to 100ms/div, it shouldn't be any problem for capturing a 1K square wave, and you can see in the image, some part of the captured waveform was really nice. My scope is modified, it's a SDS1102CML in fact, I solder a 2Mpts SRAM on it and turn on long memory mode.

And I tried a 10Hz sine wave by a JDS6600 DDS, it like a ladder wave in my scope in scan mode. It's not high frequence, so I think my scope scan mode is broken... or I am missing some other knowledge about scope scan mode. |O |O
ataradov:
Figure out what the actual sample rate is used in that mode. Some scopes would let you separately configure the memory depth, otherwise they select the slowest that is good enough to fill the screen.
vk6zgo:

--- Quote from: ataradov on May 31, 2023, 04:16:16 am ---Figure out what the actual sample rate is used in that mode. Some scopes would let you separately configure the memory depth, otherwise they select the slowest that is good enough to fill the screen.

--- End quote ---

This was the problem with the early DSOs, which reduced the sample rate at large values of time/div, so far that it dropped below the higher frequency components of a PAL analog video waveform, the resultant aliasing making the display unusable.
The first one I encountered couldn't even show a line (horizontal) waveform, whereas the later ones were better, showing a "sort of" accurate   line rate signal, but a field rate signal was a total mess. 

As the OP's signal isn't near as complex as a video waveform, I'm surprised that a modern DSO can't display it.                                                       
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