Hello, I've been getting an intermittent spindle orientation problem on an arrow 1250 w/ 2100 control during tool change for a couple years that four different service guys cant figure out. The spindle searches for home position to do the tool change and cant find it after making several revs and eventually alarms out. It will do an m19 orient every time without fail. We changed spindle drives and it didnt help. The prox switches show to be working on the switch itself and programware. Not a heat problem because it will start messing up first thing in the morning as well as in the afternoon and we have a/c in the cnc shop. Sometimes runs a month without fail, other times every other day. Any advice?

You may have tried this already. Put your M19 on a seperate line just before the M6 (tool chg. call) in your program. Sounds like to me though you have a sticky switch that is not making or an electrical intermitten short.