1990 Denford TRIAC VMC running Fanuc OM-C control.

All was working fine until one afternoon getting her to home on the Y axis was temperamental but after a few attempts she did home after which she functioned normally.

That was last weekend. Now however she will not home on Y at all. X & Z home normally. The machine hasn't been moved or messed with so I have no idea what has caused this to happen.

When homing Y the axis sets off at rapids speed until it gets close to home and then slows as you would expect. However it continues straight through zero and out the other side until the axis drive cut off switch is triggered. I don't get an over travel alarm, the servo drive relay (I presume) cuts out and I get the "Not Ready" until I use the axis override button and jog back within limits.

I have taken the front bellows off and manually triggered the two switches and diagnostic 0017 reacts changing bit 6 from 1 to zero when the proximity switch is depressed. Similarly, diagnostic parameter 0000 changes bit 6 to zero when the limit switch is triggered.

Out of curiosity / desperation I flicked through the pages of diagnostic parameters and happened to notice that 51 58, 315, 317, 320, 322, 520 & 540 are all constantly changing value with some or all bits rapidly and apparently randomly changing. No idea if this is relevant or not.

I have tried turning the control on with P and CAN depressed but it has made no difference.

Any clues what to check / test / swear at next?

Thanks!

Charlie.