oscilloscope channel 2 not working independently

[Pooyan]

Hello,
oscilloscope channel 2 not working independently.
When I remove channel 1 from the circuit, channel 2 output drops to zero. 2 channels are grounded independently using 2 channel ground pins. 
Can you please let me know what might be the issue here?

[VCSEL]

Hello Pooyan:

If you are measuring a DC voltage can you check with a meter to verify the voltage is still present?

Also check if channel 2 is AC or DC coupled or set to GND.

If you are using a trigger, check it is triggering on channel 2.  If you are using a trigger on channel 2, check if the trigger voltage is within the voltage range of channel 2. 

VCSEL

[attila]

The oscilloscope inputs are differential, but input voltage levels have certain limitations relative to device ground level.
For DC measurements common (or known) ground level is needed between circuit and testing unit.
Alternatively you could use AC input, with BNC adapter board or own capacitor.

For further details see:
https://reference.digilentinc.com/analog_discovery:refmanual
https://reference.digilentinc.com/analog_discovery_2:refmanual