Rigol Oscilloscope issue

[Centmo]

Hi, I have the Rigol DS1204B scope, which is essentially the same as the all-popular DS1052E except it has four inputs instead of two, and 200MHz bandwidth instead of 50/100MHz.

I purchased a differential probe to measure a differential signal, which looks like a square wave from 0.05V to 60V. What I am trying to do is zoom in on the 0.05V part of the waveform (the troughs) and view it on a 50mV/div scale. The problem is that once I zoom in past 5V/div, to 2V/div, it appears that the scope automatically switches from DC coupling to AC coupling (even though DC coupling is selected), and the part of the waveform I am interested in disappears off the bottom of the screen. So far off the screen, I can't move it up high enough to see it without hitting the limit.

Is this due to the fact that my signal has a high-voltage component, and I am running into a dynamic range issue? Is there anyway around this?

Thanks.

[Mechatrommer]

Is this due to the fact that my signal has a high-voltage component, and I am running into a dynamic range issue? Is there anyway around this?

are you measuring at 1X attenuation setting? if so retry at 10X setting.

[Centmo]

Thanks for the reply. The probe is set to 10X, and the oscilloscope channel also to 10X.

Here is the probe I'm using:
http://www.probemaster.com/product_info.php?products_id=62

[Mechatrommer]

i will be very very very interested looking at signal snapshot (differential signal using the stated probe, and both signal separately in CH1 and CH2 using standard rigol probe) and noise floor of the above mentioned differential probe and performance cant help you much with your problem, rigol scope can always give nasty surprises.

[nixxon]

Thanks for the reply. The probe is set to 10X, and the oscilloscope channel also to 10X.

Here is the probe I'm using:
http://www.probemaster.com/product_info.php?products_id=62

Can you read the low voltage part if you set probe to 10X and Scope to 1X?

[Short Circuit]

Dynamic range is only 10 divisions. Beyond that, you cannot trust the display anymore due to clipping/saturation effects.