Siglent 1104X-U problem with 10x probe setting

[romons]

I bought this siglent oscilloscope, and noticed after some months that at 10x probe settings, the display of the waveform is offset by about 5V upwards when I'm displaying at anything higher than 2V/line. This is true across all the channels. If I'm using the measurement display of max-min values with a waveform, these values actually change upward with the same input as I change the vertical scale from 2V/ to 5V/. There is also a 'click' of a relay during this change.

When I instead use the 1x probe setting, the problem doesn't occur. I'm properly changing the switch on the probes to match the oscilloscope setting, not that that would change the offset.

Any ideas? I don't have a schematic for the scope, so I don't really know where to begin. I already sent it to siglent, but they only tried it on 1x, and so failed to notice the problem, claimed it was fine, and mailed it back to me. $50 postage down the drain, and they seem to have ghosted me. The scope is still under warranty, but they wouldn't send an RMA package before.

Thanks for any help. I hope this is clear. Regards

[srb1954]

I bought this siglent oscilloscope, and noticed after some months that at 10x probe settings, the display of the waveform is offset by about 5V upwards when I'm displaying at anything higher than 2V/line. This is true across all the channels. If I'm using the measurement display of max-min values with a waveform, these values actually change upward with the same input as I change the vertical scale from 2V/ to 5V/. There is also a 'click' of a relay during this change.

When I instead use the 1x probe setting, the problem doesn't occur. I'm properly changing the switch on the probes to match the oscilloscope setting, not that that would change the offset.

Any ideas? I don't have a schematic for the scope, so I don't really know where to begin. I already sent it to siglent, but they only tried it on 1x, and so failed to notice the problem, claimed it was fine, and mailed it back to me. $50 postage down the drain, and they seem to have ghosted me. The scope is still under warranty, but they wouldn't send an RMA package before.

Thanks for any help. I hope this is clear. Regards

It seems unlikely that the probe itself is causing such a shift but the X10 probe might be showing up a problem with the scope preamp malfunctioning.

Switch the scope input to GND and centre the trace. Switch the V/div switch through all its ranges and note whether the trace shifts significantly. Repeat the exercise with the input open and no probe connected. Again, note whether the trace shifts significantly.

If the trace shifts with the input open but not with the input grounded that possibly indicates that the preamp input stage is damaged and excessive bias current is flowing in/out of the input stage. Excessive trace shift with the input shorted may indicate that there is an imbalance in one of the differential stages of the preamp.

By comparing the ranges where the trace shifts with the the ranges where any input attenuator relays operate it may point to which part of the preamp is malfunctioning.



 

[romons]

Thank you for your response! This was a great test. Apparently, the 10x vs 1x thing was a fluke. This happens everywhere, with basically the same offset. When the higher attenuator is switched in by relay, the offset increases 50 times. The probes supplied with the scope don't have a gnd switch position, but I had another probe with a ref input, and the result is basically the same.

This is probably just a calibration issue, right?

Thanks and best regards!

The results of the test you suggested are as follows:

No Probe, scope set to look for 1X probe

Scale    Offset
1mV     6mV
2mV     6mV
5mV     6mV
10mV   6mV
20mV   6mV
50mV   small (probably 6mV)
100mV  small
200mV  small
500mV  ~300mV (relay click, so different attenuators)
1V        about .3V
2V        small
5V        small
10V      small

No Probe, scope set to 10x

Scale    Offset
10mV    60mV
20mV    60mV
50mV    60mV
100mV  60mV
200mV  60mV
500mV  small
1V         small
2V        small
5V        3V  (relay click. this is where I noticed the problem, obviously. Oddly, it was much bigger when I sent it to siglent)
10V       3V
20V      small
50V      small
100V    small

[bdunham7]

Are the results similar for all channels?  Have you run the self-calibration routine? 

[romons]

I just ran the self-calibration, and things seem much better. The scope was still within it's calibration date window, so I didn't think of running the calibration routine.

Great lesson for me.

Thanks

[bdunham7]

things seem much better.

Can you quantify that and then compare it with the specifications?  Also, I don't have that exact model but I think there is a 'Quick Cal' option in the utility menu and that should be set to on.  This will improve accuracy during warmup and over temperature changes. 

[tautech]

I bought this siglent oscilloscope, and noticed after some months that at 10x probe settings.....

Did you also set channel input attenuation to 10x ?

[romons]

I recalibrated it after leaving it running for an hour beforehand, and the self-calibration worked very well. Now, there is basically NO offset, and all I see is expected noise around the 0V level when I try the above test.

So, problem solved. Thanks