I may have repaired a similar encoder (at least I recognise the name of the turret) before now for another forum guest. Anyway, the first thing I'd look at is if there's a pull-up on the inputs to the PLC. Gimme a sec, let's see if I have some old photos...

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If your encoder looks like one of these - essentially, unless there's a common-mode failure (e.g. supply line to the PCB) then each of the 6 signals is independent from the other - and it's highly improbable that the entire encoder has failed. I'd have to really dig around for any notes I may have but believe the encoder outputs are open-collector. If the PLC doesn't provide a pull-up, or cannot be configured to switch-in a pull-up then try with a 1k-10k resistor between DC+ and the output.

For information - the failure mode experienced by this encoder - twice over two years - was the failure of the photo-diode on the encoder board. Last pass I replaced all diodes.