yes if your camera has a problem only by exposing it to the cold, it is quite possible that it comes from the lower card which controls all the motors of the mirror and the shutter Partially disassemble the camera, first the rear cover, then the lower cover, and the front cover (Be very careful to unplug the microphone!!!) you will see under the tripod mounting plate the board responsible for your error, there may be a bad contact on the electrical sockets which must move. If it still doesn't work, it may be the shutter mechanism, it may need to be replaced.

Hello, behind the screen, there is a chip management of the screen, in case of indeterminate failure, it is advisable to change the chip, the screen, and the electrical tape, the pieces cost about $ 60. If the failure is still present, the graphics processor of the motherboard is probably defective. The repairer must know the reasons for the breakdown before repairing the unit.

hello, it's a late answer, err 20 corresponds mainly to the mechanism of the defective mirror. but the shutter may be defective, (although err 30 should be displayed), or the motherboard if the device displays err 20 after wetting the device (but this is unlikely). it can also be an electronic problem on the lower board when exposed to water.

Important !

the tutorial is good, but for dismantling the motherboard, I advise you to first remove the top cover (flash shoe and top button) before removing the motherboard, it's easier and less risky .

This is valid for the A7sii and the A7ii which are both almost identical.