diff --git a/xos/synchronizer/models/convenience/hippieossservice.py b/xos/synchronizer/models/convenience/hippieossservice.py
index 0959303..33ab09a 100644
--- a/xos/synchronizer/models/convenience/hippieossservice.py
+++ b/xos/synchronizer/models/convenience/hippieossservice.py
@@ -18,11 +18,10 @@
 # {
 #     'status': 'activate',
 #     'serial_number': 'BRCM1234',
-#     'uni_port_id': 'of:00100101',
 #     'of_dpid': 'of:109299321'
 # }
 
-from xosapi.orm import ORMWrapper, register_convenience_wrapper
+from xosapi.orm import register_convenience_wrapper
 from xosapi.convenience.serviceinstance import ORMWrapperServiceInstance
 
 import logging as log
@@ -30,18 +29,21 @@
 class ORMWrapperHippieOSSService(ORMWrapperServiceInstance):
 
     def validate_onu(self, event):
-        log.info("validating ONU %s" % event["serial_number"])
 
-        # TODO check if a service instance for this serial_number already exists
+        log.info("validating ONU %s" % event["serial_number"], event=event)
 
-        # create an HippieOSSServiceInstance, the validation will be triggered in the corresponding sync step
-        oss_si = self.stub.HippieOSSServiceInstance(
-            serial_number=event["serial_number"],
-            of_dpid=event["of_dpid"]
-        )
-        oss_si.save()
-
-
-
+        try:
+            oss_si = self.stub.HippieOSSServiceInstance.objects.get(serial_number=event["serial_number"])
+            oss_si.no_sync = False;
+            log.debug("Found existing HippieOSSServiceInstance", si=oss_si)
+        except IndexError:
+            # create an HippieOSSServiceInstance, the validation will be triggered in the corresponding sync step
+            oss_si = self.stub.HippieOSSServiceInstance(
+                serial_number=event["serial_number"],
+                of_dpid=event["of_dpid"]
+            )
+            log.debug("Created new HippieOSSServiceInstance", si=oss_si)
+        
+        oss_si.save(always_update_timestamp=True)
 
 register_convenience_wrapper("HippieOSSService", ORMWrapperHippieOSSService)