There is a problem with a metal bracket that provides grounding to all cartridges, which have slipped out of position. That bracket is located under the left side cover.
First picture represent the side view of machine. The 2nd is with the metal bracket circled. What you have to do is to reattached the bracket (eventually with some glue). Make sure to put all the springs back in their positions. It is possible, because of losing grounding, to have all the cartridges to be defective so you may need to replace them all.