When I connect the 66sr to a PC the 66sr shuts down.

[Bertbeer]

The replacement also has firmware 5.50 and chipset firmware 2.00.06.
It does not have the USB connection problem.
I am an electronics engineer and my conclusion for the fault in the previous one was that it was related to the USB power supply electronics in the GPSMAP 66sr. It was definitely not the USB connector of the device.

The replacement 66sr works as advertised apart from some software bugs that are still present in the 5.50 firmware.
I observed for instance the CPE.bin and EPO.bin files for a fast GPS fix not been downloaded when the 66sr is connected to a PC and synchronizing with Garmin express. They were however downloaded when I made a bluetooth connection with a smart phone and running Garmin Connect.