I just had this issue, tried cleaning all contacts on console and games as well as re seating the expansion pak. Still the same fault; no signal.
What did fix it was slightly lifting the cartridge up after inserting it down fully, raising it up 3-5mm and it works perfectly!
Maybe all the gunked up dust at the bottom of the console cartridge port prevents a good connection(and is near impossible to access to clean).
Aztec level here we go!
:)