Issue with auto button - always enabling channel 3

[miduchp]

Hello everyone,

I'm quite newbie. I've recently bought RIGOL MSO1104Z and I've spotted one issue. I'm not sure if I should request RMA so before I will do this, I wanted to ask about your opinion.

The problem is that whenever I will press Auto button, scope will always detect signal on channel 3. It does not matter if probes are attached on other channels or no probes attached, it always enable channel 3.

I've created 2 short movies which are showing this behavior. I'm not sure if this is an software setting, issue or hardware problem. I'm pretty sure it was not like that from begging.




I would appreciate any help with that.

Regards,
Piotr

[rstofer]

I just tried this experiment with my DS1054Z:
All channels turned off, probes disconnected.  AUTO results in no channels turned on.
All channels turned off, CH4 probe on test signal.  AUTO results in only CH4 being turned on.

How much noise do you have on CH3?  It seems like a lot.  What happens if you short that channel out?

[miduchp]

I've performed test with shorten channel 3, behavior is still the same.

I'm attaching image with noise from CH1 and CH3.



Do you think it's the hardware issue on CH3 ?

Regards,
Piotr

[alsetalokin4017]

That does seem like a lot of noise and a rather large offset for a channel with nothing plugged in to the inputs. Normally you should see a little brief "Auto Detected none!" or "function limited" message flash on the screen.

Please do the following:
Unplug all probes. Select Storage>Default, to reset the scope to a known startup state. This should automatically turn on CH1 only, with 1 us/div horizontal and 1.00V/div vertical. Then let the scope warm up for half an hour. Then run the self-calibration routine. Then repeat the "Auto" test with nothing plugged into the inputs. Problem still there? Then yes, there is probably something wrong with the scope.

[miduchp]

I've completed the steps you described and the issue is gone. Now scope just displays function limited message but channel 3 remains disabled after pressing auto without probes attached.  Many thanks!

P.S. What is the acceptable offset and noise level for this scope ? I would like to make sure it is ok while it is still under warranty.

[DaJMasta]

It doesn't detect the probes, so them being attached or not shouldn't be an issue.  There is probably an auto calibration procedure in the utility menu that can help correct any input offset or something, but I'll be honest, I'm not sure what this means: "Now scope just displays function limited message but channel 3 remains disabled after pressing auto without probes attached."

You're getting an error message after pressing auto?  Is channel 3 disabled when it's not supposed to be?

There doesn't seem to be a posted noise specification, so unless it's really heinous you probably can't RMA it on a noise basis.  I would expect to see noise on the lowest vertical scale, maybe there are some video reviews that show what shows up on other units.  Maybe there are some persistence/math functions that can show you how much noise is really there and if there's anything that's periodic.

[miduchp]

It doesn't detect the probes, so them being attached or not shouldn't be an issue.  There is probably an auto calibration procedure in the utility menu that can help correct any input offset or something, but I'll be honest.

Yes, I've executed this procedure and it helped. Offset has been fixed, Channel 3 does not get enabled when probe is not attached.

I'm not sure what this means: "Now scope just displays function limited message but channel 3 remains disabled after pressing auto without probes attached."
You're getting an error message after pressing auto?  Is channel 3 disabled when it's not supposed to be?

It's an information label after pressing auto. Without any probes attached, none of the channels gets enabled. After competing AUTO scope just displays info with message "function limited" which is fine according to the alsetalokin4017 post.

In general, after performing reset and auto calibration using alsetalokin4017 guide, it seems that everything is working fine.

I've sent the same description to the Rigol dealer in Poland, they asked me to return the scope for main board replacement. 
I think I will wait with that for couple of days, see if auto calibration removed the problem permanently.

[tautech]

There doesn't seem to be a posted noise specification, so unless it's really heinous you probably can't RMA it on a noise basis.  I would expect to see noise on the lowest vertical scale, maybe there are some video reviews that show what shows up on other units.  Maybe there are some persistence/math functions that can show you how much noise is really there and if there's anything that's periodic.

WRT the apparent visible noise:

<snipped>
Rigol have expanded from 5mV/div  to 2 and 1mV/div  reducing vertical resolution. These 1 and 2mV/div are derived from 5mV/div.