I have recently purchased a Bridgeport interact 520 VMC with Heidenhain 155 control. I had a few issues with sticky limit switches, missing parameters, tool changer not out etc which I have seemed to have overcome. Yesterday I came in and turned the machine on on it says "Z measuring device defective". This happens as soon as it tries to zero the z axis. It doesn't even move just fires off the error message as soon as the orange and green buttons are pressed.
I have traced the cable form the back of the control to near the fanuc drive on top of the machine and it seems ok. The cable then disappears down into the machine after another connector. I have removed one of the slide plates?? from the z-axis and can see the cable which then disappears down under another plate surrounding the drive screw. I cannot get the lower slide plate off as the spindle is slightly too low for me to remove the upper screws. having read various posts and threads I figured I would try and locate and clean encoder.
Am I on the correct track to solve the issue?
Is this where the encoder is located?
Is there a way to manually raise or lower the z-axis with the power to the machine off?

Any help would be very much appreciated.