Hello Jack,
How did you check the connections?
I have an old Nexstar GPS 11″ and the No Responce 16 and No responce 17 were a common occurance.
As Nick mentions the connectors are rubbish and really not fit for purpose.
I found that you have to remove and replace each connector 2 or 3 times. This wipes the surface of the connector and as mentioned there is no harm using a good contact cleaner to help.
Afterwards I used a contact grease (sparingly) before final re-connection. I have not seen a no responce message since, (touch wood).
I do not know if the CGEM uses the same or similar connectors but on the Nexstar 11″ GPS it is possible to put them back wrong so befoe doing anything take a photo so you know exactly how they are connected.
Cheers
Rob