Rigol DHO800/900 Oscilloscope Bug Reports + Firmware

[Fungus]

Sounds well like a bug to me.

It's probably deliberate. We're dealing with analog values here, there's probably some sort of hysteresis/threshold things going on the make triggering more stable on noisy signals.

I don't get the obsession with trying to label everything as a "bug". The 'scope will trigger perfectly on that signal, just turn the knob and move the level up a bit.

So what happens when you want to scope a 5kHz square wave signal that is 0.150 volt-peak? Scope can't trigger it?

...and this is the result of that type of thinking. 

Of course it can trigger. Set vertical scale so it's a decent size on screen.

[Randy222]

So what happens when you want to scope a 5kHz square wave signal that is 0.150 volt-peak? Scope can't trigger it?

...and this is the result of that type of thinking. 

Of course it can trigger. Set vertical scale so it's a decent size on screen.

What does a screen vertical scale have to do with an input signal that is 5kHz 0.150Vp with trigger set to 0.100V ?
Nothing should be the answer.

If I set the screen so that signal shows like a flat line on the screen, the input signal nor trigger level has changed, so the trigger functionality should not be impacted just because I set my screen view to something silly, etc. Trigger should not be tied to x or y screen settings, trigger should be tied to input signal.

Anyways, topic for another thread.

[csuhi17]

The test signal was provided by a TinySA Ultra.
In the video, I set the simple edge trigger.
The frequency can be seen on the side, as well as the value of Vpp.
and in the pictures you can see it at 4 frequencies.
At 125Mhz and 250Mhz, you can see that the bad triggering zone is larger, that is, the value of deltaY compared to the total Vpp.
I can't reproduce this phenomenon as strongly on another scope.

I think this has already been discussed before.
At least the two are close.

[Fungus]

If I set the screen so that signal shows like a flat line on the screen the trigger functionality should not be impacted

Says who?

On a DSO the input voltages don't go past the ADC. The trigger works with sampled values, not raw voltages.

If the signal is two pixels high on screen then why would the trigger work?

(cue all the pedants with fancy scopes that have separate analog trigger circuits inside them...)

[Randy222]

If I set the screen so that signal shows like a flat line on the screen the trigger functionality should not be impacted

Says who?

On a DSO the input voltages don't go past the ADC. The trigger works with sampled values, not raw voltages.

If the signal is two pixels high on screen then why would the trigger work?

(cue all the pedants with fancy scopes that have separate analog trigger circuits inside them...)

If the signal is not even on the screen, the signal is still however being input to the front end and can still be processed. This issue has to do with single "threading" signal processing. What you see on the screen should be a seperate process from actual signal processing.
Anyways, no need to debate this here.

[norbert.kiszka]

In case of fast unstable gen with avg acquisition:

[Aleksandr]

In case of fast unstable gen with avg acquisition:

.

Have you tried increasing the memory depth?

[norbert.kiszka]

Have you tried increasing the memory depth?

Same problem at 50Mpts.

[Bud]

If I set the screen so that signal shows like a flat line on the screen the trigger functionality should not be impacted

Says who?

On a DSO the input voltages don't go past the ADC. The trigger works with sampled values, not raw voltages.

If the signal is two pixels high on screen then why would the trigger work?

(cue all the pedants with fancy scopes that have separate analog trigger circuits inside them...)

If the signal is not even on the screen, the signal is still however being input to the front end and can still be processed. This issue has to do with single "threading" signal processing. What you see on the screen should be a seperate process from actual signal processing.
Anyways, no need to debate this here.

Fungus is correct here. What you see on the screen is what actually goes into the ADC. If you set input attenuator so the signal looks small on the screen, that in reality means the ADC receives small signal which may not be sufficient to trigger on after it gets digitized. What you say should be is just wishful thinking and is not how it works. Even in scopes which have a separate trigger channel, it is still tied to V/ of the signal channel and gets accordingly attenuated as you change V/.

[Mechatrommer]

with the success of my diy LA probe https://www.eevblog.com/forum/testgear/low-cost-compatible-rigol-pla2216-logic-probe-for-dho900-(and-hacked-dho800)/msg5352677/#msg5352677 i noticed one bug in LA GUI, whenever we set threshold other than 0, let say 3V, when we switch off the dso, switch on again and activate LA GUI, it saved threshold (non zero) we set earlier, so far so good. but probing threshold voltage level going into comparator (internal of LA probe) and playing on actual signal probed with LA, the actual threshold is zero! even if in GUI its non-zero, the workaround is we need to set the threshold again and hit OK without changing value, to make the dso send the correct threshold voltage into the comparator circuit, fwiw.

[ebastler]

Did you have the probe already connected when the scope was powered on? Maybe the power-on initialization only sets the logic analyzer parameters when it sees a probe. (And Rigol does state that the probe should not be hot-plugged anyway.)

But of course it is entirely possible that there is another little bug there...

[jsobell]

If I set the screen so that signal shows like a flat line on the screen the trigger functionality should not be impacted

Says who?

On a DSO the input voltages don't go past the ADC. The trigger works with sampled values, not raw voltages.

If the signal is two pixels high on screen then why would the trigger work?

(cue all the pedants with fancy scopes that have separate analog trigger circuits inside them...)

This dreadful! With noise rejection on A 3V Sine wave from the signal generator at almost full-screen won't trigger below -1.2V! That's almost 10% of the bottom of the waveform, yet it triggers perfectly at the top of the waveform (1.48V)
There is definitely something very wrong with the triggers. There is no reason for the discrepancy between the top and bottom of a sine wave.

[ebastler]

This dreadful! With noise rejection on A 3V Sine wave from the signal generator at almost full-screen won't trigger below -1.2V! That's almost 10% of the bottom of the waveform, yet it triggers perfectly at the top of the waveform (1.48V)

There is definitely something very wrong with the triggers. There is no reason for the discrepancy between the top and bottom of a sine wave.

This has all been discussed before, probably on this very thread. I seem to recall that the asymmetry in the trigger behavior changes with the polarity of the active edge you select for the trigger. I.e. when you switch to falling edge, the trigger will not work near the maximum of the signal.

There is some logic to this: The trigger hysteresis is implemented such that there always needs to be some "runway" for the signal as it approaches the trigger threshold. Whether or not it keeps changing further beyond the trigger threshold does not matter.

I don't consider this a bug.

[jsobell]

You're right. I just powered up my Siglent SDS1204X-E and it has exactly the same behavior.
In all the years I've used these scopes I've never noticed that before!
Thinking about it, when looking for small transient spikes I have sometimes had to set it to falling edge to catch them at low levels, but I always assumed it was something I was doing wrong, rather than the behavior of the triggers.

Thanks,
 J.

[shapirus]

In all the years I've used these scopes I've never noticed that before!

Now you will, and you will have to live with it from now on. Thank the forum :)

[Mechatrommer]

Did you have the probe already connected when the scope was powered on?

yes. but i tried again just now without LA probe connected and turning on the dso, and then hot plugging the probe.. same thing, dso will show up "LA Probe Connected" message and then i can operate LA. but during hot plugging, the message popped up and disappear several time indicating intermittent hot plugging by hand which imo is not so ideal, so yes on safer side, its better soft plugging and leave the LA probe there. btw, when the probe connected, the comparators will increased temperature in open air maybe up to 60degC or so, fwiw ymmv..

[Aleksandr]

Did you have the probe already connected when the scope was powered on?

yes. but i tried again just now without LA probe connected and turning on the dso, and then hot plugging the probe.. same thing, dso will show up "LA Probe Connected" message and then i can operate LA. but during hot plugging, the message popped up and disappear several time indicating intermittent hot plugging by hand which imo is not so ideal, so yes on safer side, its better soft plugging and leave the LA probe there. btw, when the probe connected, the comparators will increased temperature in open air maybe up to 60degC or so, fwiw ymmv..

Can you post the logic analyzer PCB files? Or maybe they can already be downloaded somewhere?

[jsobell]

Is it just my 924S, or does everyone see this issue?
Run the test signal into CH1, and enable CH2 with no probe attached.
Set the timebase to 50ms, so the scope enters roll-mode, and the screen shows CH2 'smeared' down to CH1's value.
Here's what I see when I try it:
https://youtu.be/pMFDayEhk_Y

[AndyBig]

Is it just my 924S, or does everyone see this issue?
Run the test signal into CH1, and enable CH2 with no probe attached.
Set the timebase to 50ms, so the scope enters roll-mode, and the screen shows CH2 'smeared' down to CH1's value.
Here's what I see when I try it:
https://youtu.be/pMFDayEhk_Y

On my 814, modified to 914, I don’t see this. What is the firmware version on your oscilloscope?

[norbert.kiszka]

Is it just my 924S, or does everyone see this issue?
Run the test signal into CH1, and enable CH2 with no probe attached.
Set the timebase to 50ms, so the scope enters roll-mode, and the screen shows CH2 'smeared' down to CH1's value.
Here's what I see when I try it:
https://youtu.be/pMFDayEhk_Y

Tried to replicate this with 924S with firmware 00.01.02.00.02 in many attempts with no luck. However, once CH1 was shifted upwards for one roll - another bug?

Maybe You have random short between two channels on ADC, because of too much solder, but its my guess.

[AndyBig]

Maybe You have random short between two channels on ADC, because of too much solder, but its my guess.

It’s unlikely, because this doesn’t appear in all modes.

[norbert.kiszka]

Maybe You have random short between two channels on ADC, because of too much solder, but its my guess.

It’s unlikely, because this doesn’t appear in all modes.

I checked Dave photos and looks like its (very little) possible only between those LC filters. Of course I cant see below ADC IC, but there is no reason to be any traces there.

Edit: added photo fragment.

[csuhi17]

924S firmware 02.00.02 I did not manage to cause the bug.
I tried all the settings combinations that I could think of and it didn't work.

If you set a measurement to channel 2, does it measure anything?
For example Vpp or frequency?

[AndyBig]

It seems that something similar was mentioned earlier among oscilloscope bugs. Either here on the forum, or in one of the videos. But that was a long time ago, on one of the old firmware versions.

I checked Dave photos and looks like its (very little) possible only between those LC filters. Of course I cant see below ADC IC, but there is no reason to be any traces there.
Edit: added photo fragment.

Well, these LC filters belong to the same channel, so there certainly can’t be a problem with them
Although in general, excess solder may well end up on the board. This is what I found on the board of my oscilloscope when I recently took it apart.

[Mechatrommer]

previously running old version v1.14 for DHO924S... now running latest version v0.1.2.0.2 digital trigger (D0-D15) was working before, now its not working, it keeps changing back to analog signal (CH1-CH4)