I load the plugin configuration, click on the y axis, then under index homing is encoder pulses/Rev, I've changed this figure but it makes no difference. Am I in the correct place?

Yes, that is correct.

Have you also changed Mach's Counts per unit to match the new encoder, and is the Y axis working except for index homing?

Allan

No, I haven’t . Where is that setting?

Sorry yes, y axis looks to be ok apart from scale being wrong

I have changed the steps per on the motor tuning and setup page, oddly this made no difference

This is making no sense to me: how can your servo operate correctly if the steps per unit has no effect? Is the same encoder used by both your servo amplifier and your CSMIO, or do you have separate encoders for each? Is the CSMIO encoder input fed directly from the encoder or via an encoder output of your servo drive?

I think you need to go back to the CSMIO plugin and check that your Y axis is configured to use the proper encoder channel.

Allan

The encoder doesn't connect to the servo amplifier, it only connects to the CSMIO, unless there is another encoder built into the old bridgeport servo's?? I'll go an check the cables in the workshop

ok I've doubled checked the wiring, there is only 6 cables going to the servo, so no built in encoder there. I've also double checked the encoder is connected to the right input on the CSMIO.

I also tried disconnecting the encoder, which resulted in the machine not able to detect move moment of the Y axis so I get a PID error as expected. So I'm sure the machine is looking at the correct encoder, but can't understand why the changes I'm making to the config are not having any affect?

I've had a quick look through the XML config, and I can see the values I'm chaning in MACH3 are updating in the conifg

EncPPR1 and Steps1 are of the value

From your description it sounds as if you have wired and set everything correctly. I assume that you have powered your encoder with 0V and +5V from the CSMIO.

Can you verify with your DMM that the CSMIO is actually getting the differential index pulse (both +ve and -ve) from the new encoder?  Assuming you are using plugin 2.910, as you said the system was several years old, I think the CSMIO diagnostic contains a page that indicates how many counts from the limit switch opening occur before the index pulse is received. These values should be nominally half a motor turn (approximately 4096 pulses).

If CSMIO is getting the index signal but is not responding to it, I think it is time to check the CSMIO itself. To do this you would need to connect the encoder to a spare channel on the CSMIO and then program this channel as the encoder input in the plugin config.

Allan