Lost VAR1 in TIU

when thumbwheel is depressed channel does not come alive. 

It's not necessary to press the thumbwheel while changing voltage for a variable channel.

Is it possible I've somehow turned off this channel with out being aware of doing it?

No, it's not.

Did the variable channel ever work or are you trying to use it for the first time?

If it's the first time, are you certain that you actually entered the information correctly when you created the TIU Track for Variable #1? If you're not certain, delete the TIU Track and recreate it.

To just check the channel quickly, change it to Fixed Mode as follows:

Menu/System/DCS Setup

Scroll to the TIU, if you have more than one, and press the thumbwheel

Scroll to Variable 1 then press the FXD soft key

Now, do not use the TR screen at all. Just put voltage into Variable 1 input and measure the output.

Variable channel has worked for 7 plus years: used to power catenary for entire layout.  Entire overhead at same potential.  Method used to isolate electric locomotives is to open common return in block where each is stored.

Can't use your trick, my software version does not have FXD options on soft key menu when scroll to Variable 1. Guess channel is gone.

TIU is mounted on panel with all wiring behind same.  Don't care to rewire panel so my fix is to parallel next adjacent constant channel with BLK @ WHT jumpers (Red / Red & BLK / BLK) at input & output side of TIU.  Now must control voltage with MTH-4000 and have lost ability to use Handheld when running older Lionel convential electric locomotives. 

Thanks for suggestions.

Can't use your trick, my software version does not have FXD options on soft key menu when scroll to Variable 1..

Not so fast. Unless you're using a DCS version of 2.x, that soft key is preesent. In fact, if memory serves, it was even present under DCS 2.x.

You're looking in the DCS SETUP menu, correct?