Question

Does that mean pull the cards out and put them back in or are you saying send them in for repair? If you're saying pull them out and put them back in, should the mixers be on or off?

Answer 1

Just pull them out and fix them again after a visual control of the slot, the card and especially the ports/connectors. The cards might have got loose somehow, which can affect their functionality. The mixers should be off, certainly.