My dcs system comprises a Z 4000, 1 TIU and 3 AIUs. The relays in the AIUs power Z1000 switch motors. The switch motors are powered independently by a ZW. All AIU ports contain 1/4 watt resistors to provide constant lighting to the Z1000s. Last week the switches in the first AIU stopped working although I could here the relays opening and closing within the AIU. Also the switches powered by the second and third AIU continued to operate normally with the handheld. Strangely, those turnouts wired for non-derailing continue to function properly. None of the turnouts from AIU 1 light up , but all in AIUs 2 and 3 do. All wiring,both hot and common, appear intact and tight. Do AIUs have fuses? Do they wear out? Can anyone shed some light on this problem and perhaps a plan to get AIU 1 back up and running. Thanks for any help.