Problem of Analog output

[Enhorse]

Hi,

I have a problem with analog outputs. I am using two USB-6366 for my projects.

Recently, analog output of one of my unit does not work properly.

For example, it does not correctly make output voltage. If I set 4 cycles of tone bust with the maximum amplitude of 2 V, the actual output is less than 0.5 V and the shape is also not correct. Please see the below screen shot.

If I make same signal with low amplitude, such as 0.3 V, then the output is correct.

(For this text, I directly connect AO to AI on the same DAQ.)

This problem shows only one of my DAQ and the other one works properly.

One of the possible cause is a electrostatic discharge. When I test with this unit, I usually connect my analog output (AO) to piezoelectric disc (PZT). One day, I connect the positive line of AO to the positive line of my PZT. Then, I connect the negative line of AO to the negative line of my PZT. At that moment, I saw small spark.

Can it be a cause of the problem?