After a crash I cannot establish a connection between the drone through its microUSB port. It will not connect to the DJI GO 4 app for the firmware update, not will it connect to the DJI Assistant 2 from my mac. I have this problem with two different Camera Gimbal units, so I guess deduction tells me that there is a problem with the ability of the drone to transmit, that is to say, something on the other side of the camera gimbal. Love to hear some ideas, and thanks!

I'm not sure what you mean by two different gimbal apps..  But first, have you tried a different cable?  

Tried multiple cables, didn't say gimbal apps, rather camera gimbal units. I have two of them.

I'm afraid that the performance cannot be ensured after the crash. Please kindly start a case and send the unit in for inspection and repair: https://www.dji.com/support