Digital Signal

Try tethering your remote to the TIU. Sounds as if the board is not seated.

Do they run okay conventionally? Have you run a signal test? Are your loops wired in blocks? Are you using the tiu to actively pass power to your loops or only passively to inject dcs into your powered loops?

18X24 is a decent sized layout. But certainly manageable with 2 TIU’s. 14 gauge should be up to the task. Your previous layouts you said worked fine. But did this new one ever work ?  Your running 4 loops using buss wiring. Nothing wrong with buss wiring. My own layout uses it.
Do any of the 4 loops work as far as finding an engine ?  Do the loops connect in any way with the use of turnouts ?   To not have any signal strength at all to find an engine. It almost seems like something somewhere is connecting your tracks and you have multiple channels feeding the same tracks.
Are your loops blocked ? Or does one channel feed the entire loop ? Your 8 available channels should be able to cover a layout this size. Seeing you have multiple loops. I would focus on getting one working properly. Even if it means disconnecting the others to troubleshoot. Remove any cars on the loop your testing and pick out an engine with squeaky clean wheels and rollers and hopefully it will fire up and you can do a signal test.

Thank you, thank you all your comments and advice. It all helped. You helped me get my head on right. I started to think more systematically with troubleshooting techniques. It appeared to be isolated to one of the TIUs because all the problems on two loops were served by the one TIU. Thinking I had a TIU problem, I swapped the TIUs…Nope same problem. Whew, didn’t want to buy another TIU. In swapping the TIUs, I inspected the wire connections at the output terminals. Both were wired the same way. But, I had forgotten that I had inserted a bare wire the hole in both terminals vice using a fastener. The connection appeared good enough, but perhaps only for an electron flow. So, on both channels and on both positive and ground terminals, I pinched clips that I use everywhere else to make a good connection. It worked! On both affected loops, engine response was immediate and I now have fine control of the engines as the DCS was designed. The connection was not quite good enough for a digital signal to pass through. How dumb could I be? Live and learn, but what a relief. My buss wiring was effective after all. Whew.

Thank you all for your time. Your thoughts were really helpful and were particularly helpful in allowing me to step back and think it through. This forum is simply awesome. It sure pays to query the experts out there. It’s the intangible which makes this hobby AWESOME!