From time to time, when using the Neon transfection system, I do not see the side electrode "pulsing", which I would expect to see sometime between pressing the "start" command and receiving the "complete!" reply. Whenever there are no clear electrode pulses, my cells are not successfully transfected.

In the set-up, all the connections are as they should be; the tip contains an appropriate concentration of cells in the correct buffer and is free of air bubbles; and the machine has worked in the past with clearly visible pulsing and subsequent successful transfection. The lack of pulsing appears to occur randomly. Has anyone else previously had the same issue with this machine and found a cause?

Thank you in advance.