Working on another i3v - Identical to my 8" except it's a 10", bought at the same time last summer. We were having problems with the G29 not working. When you run the g28, homes all axes normally. when running g29 directly after g28 using the pronterface terminal:

*x axis moves into position, but y axis stays at home position (Y0, where the probe points are at y50, 100 and 150 for a 9x9 grid in the firmware).
*probes the 3 X coordinates given in the firmware but the y axis never moves. So it probes 9 times moving back and forth in a line at y0.
*at that point the nozzle is still at y0 geographically but thinks it is at y150 per the LCD, where it would normally be at completion of successful ABL

Comments:
*This firmware works correctly on my 8".
* i checked the wiring, everything is identical. endstops are on the same ends, set up to home at the back right corner just like mine. bone stock i3V basically except the servo upgrade.
*the 10" printer works fine and prints with fixed z endstop and stock firmware when flashed.
*everything moves around fine under pronterface control.

We're stumped and appreciate any ideas. Thanks.