my unit is not the same as this photo you had. i have removed the back but the circuit board is mated to the display and i can not see any means to remove the circuit board from the display. if there is are screws holding it to the display i can not find these and i see no way to remove it. it might not be a ribbon cable it might be contacts. that would be one reason for the contact problems. both units are doing the same. i kept the units on the dash board of the truck for several years and i suspect that the sun has warped the case. and with the case flexed from warp-age then the contacts and or ribbon cable is not making the correct connection.
i feel this is the only problem with the units. aside from short battery life.