if you can get the M15 serial number on the tag on the back support at centroid can tell you what upgrades have been made they know of, and what you upgrade options would be.
I have an opportunity to purchase a knee mill with a Centroid M 15 control. By the serial number it appears to be at least 12 years old. Has anyone updated one of these controls or at least have some information on their reliability? As a worst (expensive) case, it appears I could use one of the Ajax mill kits.
If it's the one across the river and up the hill, which was recently listed on eBay, then I have a little history for it. Software will be DOS-based, CNC7 v5.24 or similar. For about $395 it could be updated to CNC7 v7.17 without changing the motherboard.
With a new motherboard it could run the latest Linux-based CNC10 software. Cost for that upgrade path is about $2,400 installed.
The main reliability challenge is keeping the console clean and cool. The PC motherboard, CPU7 controller board and the servo drive are all located in the console on the arm. You need to keep the cooling fans running and the filters clean.
If you don't mind making a project out of it you could dismantle the M15 console and use the original 3-axis DC servo drive as the basis for an MPU11-based Ajax control.
However, if you wanted to go that route you would probably be better off just buying a DC3IOB or the new DC All-in-one so you would have a PLC too. The PLC in that M15 is a 1-in/2-out "PLC Lite", which is not supported with MPU11.