diff --git a/ams/core/model.py b/ams/core/model.py
index 9053c697..371d3dd3 100644
--- a/ams/core/model.py
+++ b/ams/core/model.py
@@ -6,7 +6,7 @@
 import warnings
 
 from collections import OrderedDict
-from typing import Iterable, Sized
+from typing import Iterable
 
 import numpy as np
 from andes.core.common import Config
@@ -16,6 +16,7 @@
 
 from ams.core.documenter import Documenter
 from ams.core.var import Algeb
+from ams.utils.func import validate_keys_values
 
 logger = logging.getLogger(__name__)
 
@@ -260,7 +261,7 @@ def alter(self, src, idx, value, attr='v'):
         else:
             self.set(src, idx, attr=attr, value=value)
 
-    def find_idx(self, keys, values, allow_none=False, default=False):
+    def find_idx(self, keys, values, allow_none=False, default=False, allow_all=False):
         """
         Find `idx` of devices whose values match the given pattern.
 
@@ -284,40 +285,27 @@ def find_idx(self, keys, values, allow_none=False, default=False):
         list
             indices of devices
         """
-        if isinstance(keys, str):
-            keys = (keys,)
-            if not isinstance(values, (int, float, str, np.floating)) and not isinstance(values, Iterable):
-                raise ValueError(f"value must be a string, scalar or an iterable, got {values}")
 
-            if len(values) > 0 and not isinstance(values[0], (list, tuple, np.ndarray)):
-                values = (values,)
-
-        elif isinstance(keys, Sized):
-            if not isinstance(values, Iterable):
-                raise ValueError(f"value must be an iterable, got {values}")
-
-            if len(values) > 0 and not isinstance(values[0], Iterable):
-                raise ValueError(f"if keys is an iterable, values must be an iterable of iterables. got {values}")
-
-            if len(keys) != len(values):
-                raise ValueError("keys and values must have the same length")
+        keys, values = validate_keys_values(keys, values)
 
         v_attrs = [self.__dict__[key].v for key in keys]
 
         idxes = []
         for v_search in zip(*values):
-            v_idx = None
+            v_idx = []
             for pos, v_attr in enumerate(zip(*v_attrs)):
                 if all([i == j for i, j in zip(v_search, v_attr)]):
-                    v_idx = self.idx.v[pos]
-                    break
-            if v_idx is None:
+                    v_idx.append(self.idx.v[pos])
+            if not v_idx:
                 if allow_none is False:
                     raise IndexError(f'{list(keys)}={v_search} not found in {self.class_name}')
                 else:
-                    v_idx = default
+                    v_idx = [default]
 
-            idxes.append(v_idx)
+            if allow_all:
+                idxes.append(v_idx)
+            else:
+                idxes.append(v_idx[0])
 
         return idxes
 
diff --git a/ams/models/group.py b/ams/models/group.py
index 2a7b5458..f944618c 100644
--- a/ams/models/group.py
+++ b/ams/models/group.py
@@ -241,7 +241,6 @@ def find_idx(self, keys, values, allow_none=False, default=None, allow_all=False
         indices_found = []
         # `indices_found` contains found indices returned from all models of this group
         for model in self.models.values():
-            print(model)
             indices_found.append(model.find_idx(keys, values, allow_none=True, default=default, allow_all=True))
 
         # --- find missing pairs ---