On the 10, you can disable the soft limits on power-up by holding - and . at the same time, then press power-on. You should see an IPL menu. Key in 4, then INPUT. You should see something to the effect of "Check soft OT at power on?" Press N (for no), then INPUT. Press 6 to end the IPL. The control should boot up, and if you look at the position page, the MACHINE positions should now read 0. Try your zero return routine.