to add to what lumberjack posted i'd like to say in my own experience working on zapi controlled systems i've seen issues in the same areas he spoke of but also you may want to check the connections where the cables connect to the controller and make sure none of them are loose at the standoff. You can grab the cable and wiggle it a little bit and watch the bolt and where the standoff comes out of the cover and if it (the standoff) turns at all or is loose at all then the stand off is broken away from its mounting and the controller will have to be replaced. If the cable is loose and the standoff is still ok then just tighten the cable back up.
These standoffs are cold soldered to the positive and negative plates inside the controller and can break loose if put under any abnormal torque when checking tightness during PM's etc.
I've also encountered some problems with the ribbon cables inside the controller that connects the circuit boards together, they can come loose from vibration. zapi came out with a bulletin at some point in the past informing all service personel about it and had instructions on how to repair this. Basically you remove the cover, put the cables back into their respective ribbon connectors and then apply silicone to the cable and connector so insure they stay in place. Just remember if you go into the controller be extremely careful when taking the cable nuts/bolts loose. Most of the one's i've seen have a hex shaped part of the standoff to put a wrench on so you can hold it in place while loosening or tightening it, by all means use this method and don't risk it otherwise.