From HELP:

**Setting the value of a control by using a macro or Visual Basic doesn't
trigger this event for the control. You must type the data directly into the
control, or set the control's Text property.

So using code to set/change the value of [TestInSystem] won't work.... the
change event won't fire.

BTW, this:

If Me.TestInSystem = -1 Then           ' "Yes" condition
    Me.Text1169.Visible = True
    FrameStatusWAVE.Visible = True
    Else
    Me.Text1169.Visible = False         ' "No" condition
    FrameStatusWAVE.Visible = False
End If

can be shortened to two lines:

    Me.Text1169.Visible = Me.TestInSystem
    FrameStatusWAVE.Visible = Me.TestInSystem

This is how I might do it (one way...):

Private Sub Check0_AfterUpdate()
  Set_Visible
End Sub

Private Sub Check2_AfterUpdate()
  Set_Visible
End Sub

Private Sub Check4_AfterUpdate()
  Set_Visible
End Sub

Private Sub Check6_AfterUpdate()
  Set_Visible
End Sub

Private Sub Check8_AfterUpdate()
  Set_Visible
End Sub

Private Sub Check10_AfterUpdate()
  Set_Visible
End Sub

Sub Set_Visible()

 'TestInSystem is set to TRUE if the sum is < zero
 'TestInSystem is set to FALSE if the sum is = zero

  'this should be one line
  Me.TestInSystem = (Nz(Me.Check0, 0) + Nz(Me.Check2, 0) + Nz(Me.Check4, 0)
+ Nz(Me.Check6, 0) + Nz(Me.Check8, 0) + Nz(Me.Check10, 0)) < 0
 
 ' hide or show controls
  Me.Text1169.Visible = Me.TestInSystem
  FrameStatusWAVE.Visible = Me.TestInSystem

End Sub

Instead of hiding the controls, you might set the Enabled property:

  Me.Text1169.Enabled = Me.TestInSystem
  Me.FrameStatusWAVE.Enabled = Me.TestInSystem

That way, the field is still there but data cannot be entered. Sometimes it
is less confusing to have controls disabled and not appearing and disappearing

HTH