1. The settings in your video are completely different in the second half of your video. This is plainly obvious in the video you posted.
2. I suggest you spend more time understanding how this instrument works.
You have noticed everything very correctly! )
1. Yes, this is the cause of the cursor disappearing problem. I did not rebuilded the Trigger->Setup->Coupling to "AC". It happens somehow without my direct participation. And such surprises get in the way of work.
2. Yes, and I agree with that. Studying the device is a good thing)
1. No, it do not happen itself. It have changed due to your action. Directly or indirectly, wirth its own it do not change. It is not human what can accidentally or by intuition do some unexpected or just totally irrationally.
2. Studying is important. "Know your instrument" is not said without reason.
In first place I can easy tell you "turn Trigger coupling to DC and your problem is away" But, because these trigger things are one of most important things to understand I try you hit it yourself because after then it is fixed better in your memory.
Some times when I give some guidance in real life I tell "Keep trigger coupling always DC UNTIL you know exactly you need AC coupling". But then it also need be careful with this advice. Because this is highly dependent what you are doing with scope.
In some cases, specially if playing with scope with unknown signal and probing fast this and that... some times Trigger coupling AC is better for these very simplest things when we use very common simple edge trigger like we have done tens of years with analog scopes etc. With modern digi scopes we need learn more and stop using it like old analog scope - mostly.
In developing etc lab we normally know lot of about signals what we are looking. But example in some repair work, situation may be very different specially if we do not follow tightly some repair service manual, then we are like in dark forest and probing this and that and there is some times important this "idiot proof" trig what was in analog scopes just normal... least with Tektronix who was king of trigger hill.
Also scope factory default is trigger coupling DC. Perhaps TRIGGER coupling change back to DC if you have done factory default or default depending how you have "programmed" this secondary default buttton. Also I do not remember how this model AUTO button set it but perhaps it force trigger coupling to DC.
Or perhaps in some phase you have thinked you set trigger source to AC (as can see you have there tested 50Hz AC signal and these cases some times is wise to use
trigger source AC) but you have changed accidentally trigger coupling AC but this accident can not easy happen in setup menu system.. they are so different place, if this happen it is human random mistake or what ever...
Just thumb rule "Keep trigger coupling DC until there is reason for AC coupling".
Remember that there is Channel AC and DC coupling what can handle most cases.
And it have nothing to with TRIGGER AC/DC coupling. In ALL cases, if input is AC or DC coupled, TRIGGER is looking only digital 8 bit data what is after ADC and nothing else and there this data stream values between 0-255 and this data is - you need think it is "DC coupled" independent of input AC/DC coupling. It is "DC coupled" if you look it with trigger engine eyes.
In analog scope (simplified), input AC coupling makes also trigger AC coupled but trigger AC coupling do not make inputs AC coupled because this trigger AC coupling is in trigger signal signal pathway.
But, in full digital side trigger DSO, input AC/DC do not affect at all trigger coupling. Trigger coupling is always after ADC and input AC DC coupling do not affect there. Data stream is always between 0 - 255. (irl 2's complement) Now there in data stream is signal changing and there we can then think how we filter this data for trig. And in first place there after ADC (in this stream what is going to trigger system) AC/DC/LFreject "coupling" filter and HF low pass filter. Of course main stream from ADC to memory goes directly. (except that there can be other kind of DSP filtering. In some scopes there is user adjustable LPF/BPF/HPF and some other things, also some more intelligent things).
Thre is on and BIG Achilles in these systems. All we know frequency aliasing when ADC see over Nyquist limit frequencies, other words over sampling frequency/2 frequency components and then we see some not wanted things on screen. (this is totally different than image aliasing due to display pixels and displayed data what image antialiasing oscilloscope can also have).
But this freq aliasing we see with our eyes on the screen... specially when ADC data is decimated for reduce displayed sampling rate. All understand it and know it, if not, sad.
But there is other thing. Digital trigger system "eyes" are looking ADC data stream. If ADC have seen in its inputs higher than true samplerate/2 frequencies this data stream from ADC include these alias frequencies! This may disturb digital trigger engine.
There is no way to know what is alias and what is true. There is not simple way to detect this without some further information. But this normal 8 bit data stream do not have this information. It have only 8 bit raw values and that's all. How DSP filter know what is alias and what is not. Think about it.
Analog side pathway trigger system do not have at all these some bad things but it have some other bad things or poor things, specially if it is cheap and simple.
After example older DSO or after analog scopes some things need forget and some things need learn. If still use both, like me, must not forget anything but keep all them parallel in memory.
In this case there was SDS1202X-E. This scope have 2 totally different trigger systems.
2 main channels have pure full digital side trigger system "trigger engine".
Ext Trig is totally different. It is conventional analog pathway - and analog comparator trigger system. This Ext Trig is very simple and performance is far away from main channels full digital side trigger functions and very reduced performance in many ways.
In full digital trigger system first advantage is that trigger engine see perfectly same digitized waveform data what is also data for display this signal. In conventional analog side pathway trigger system analog comparator can see different signal what ADC see, specially with higher frequencies, fast edges etc. Of course it can do very perfect but it is very challenging and not cheap.
Disadvantage (other than aliasing) is in digital trigger that trigger is absolutely limited to ADC scale. If signal is over ADC FS it can not even try to trig. If ADC output is constant 0xFF trigger game is over but still before ADC there can be nice signal. After ADC trigger, system is totally blind for all this. (if we do not take some information from before ADC)
Least what manufacturers need do is warning about Clipping! but many do not even this. Siglent, please... do it.
But conventional analog trigger can still happy see there signal what can trig depending its dynamic range.
Sorry after edit and rewrite etc this is now bit messy...
Perhaps some day these trigger basics need write so that they all are explained clearly, simply and in good order with some example images and drawings.
It is sad today usually manufacturers do not anymore make User Reference Manuals where are every single details explained with perfect data and even math if need. Today even these normal level User Manuals are - with one word - poor.
Perhaps reason is due to fact that no one read these and today this continuous developing FW ... no one can keep these manuals up to date. As can see...
BTW, new User Manual is for all SDS1000X-E and X-U models. So who ever have old manual please use this more new one.
SDS1000X-E/SDS1104X-U User Manual version UM0101E-E05A July, 2020At this time this new UM can find only in SDS1104X-U documents (least in Siglent EU area official sides). SDS1000X-E documents list have only older manual.
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