Kind of sounds like you're not powering up the tiu . The TIU need a power supply to turn on, operate /function.
2 ways to turn it on.... power to fixed 1 or an aux power supply
. Nothing works unless the tiu is powered up...Fixed 2 is a straight through connection so even though power flows through it the tiu is still dead and there's no dcs signal. The Var channels are also dead.
Bottom line make sure the tiu is turned on by checking out the led on the top of the tiu.