fields empy when change product in purchase

purchase.py

@@ -101,7 +101,10 @@ class Line(metaclass=PoolMeta):
             self.product_equipment = False
             self.address_equipment = None
             self.serial_equipment = None
+            self.software_version = None
+            self.health_register = None
             self.refurbish = None
+
             return
 
         party = None

sale.py

@@ -6,7 +6,6 @@ from decimal import Decimal
 from trytond.modules.product import price_digits
 from trytond.transaction import Transaction
 from trytond.exceptions import UserError
-#from collections import setdefault
 
 from trytond.wizard import (
     Button, StateAction, StateTransition, StateView, Wizard)
@@ -117,7 +116,8 @@ class SaleLine(metaclass=PoolMeta):
 
     product_equipment = fields.Boolean("Product Equipment")
     equipment = fields.Many2One('optical_equipment.equipment', "Equipment",
-                                domain=[('state', '=', 'registred')],
+                                domain=[('state', '=', 'registred'),
+                                        (Eval('product'), '=', Eval('_parent_sale.line.product'))],
                                 states={'invisible': If(~Eval('product_equipment'), True)},)
     address_equipment = fields.Many2One('party.address', "Direccion")
     unit_digits = fields.Function(fields.Integer('Unit Digits'),