homing: y-works ok, x-movement very slow.

I have identical x and y axis (same type of motor, same type of switches) ,same config. With
G28.2 Y0
the Y homing works ok, and takes few seconds.
with
G28.2 X0
the X homing works, but the motor runs at very slow speed (1 % of what it should). The homing swithh signal Xmin works ok, I cerified it with multimeter (3.3v when in home-position).
The configuration of homing is:

$xsx 0
$xsv 500
$xlv 100
$xlb 50
$xzb 10
$ysx 0
$ysv 500
$ylv 100
$ylb 50
$yzb 10