[codyst]

If you look at the parameters you are telling the control to look at optical scales and switching off the encoders. A quick check on scale machines for disconnect alarms is to switch the encoders back on. Often the machine will then run fine, albeit with less accuracy than before. I've often had to do this for customers with OKK machines whilst waiting for a production stop to get on the machine to sort it out.
Alan B

I've never seen any machine set up so that when the OPT bit is set to a 1 that it "shuts off" the encoders and looks at the scales only. Every machine I've ever set up with scales has parameters for resolution of the scale (read), and the amount of allowable Synch error between the encoder and the read of the scale.

[mif73]

when using scale, the encoder is still used to monitor motor speed as a tacho.
The cnc compares movement from the encoder to the scale, if the motor is moving, but no feedback signal comes back from the scale within a preset distance, you get a disconnect alarm, this can be caused by excessive backlash and the alarm detection level can be compensated somewhat by parameter.(or the scale may be faulty).

As for the 434 detect error alarm , check dianostics 720-727 and see which bit is a 1 when the alarm occurs.
If you can't clear the alarm by pressing reset or just power off /on the cnc while leaving the main machine power on, then the alarm will be displayed on the servo drive pcb for the Z axis and can be cleared by main power off/on.

Hope this may be of help.

[h_butter]

I have several amchines that utilize both glass scales and absolute motor encoders and they perfoem exactly as stated above. This is a safety feature that if the motor is running and scale signal doesn't you get the error another type of error is a disconnect and this may refer to a popped clutch on the spindle/ball screw.