TMCC/Legacy Track Signal Booster as a diagnostic tool
First, let me say that I hate long forum posts. And I am now going to violate my own rule . . . So if you are short on time, skip down to the Cliff Notes at the bottom.
I finally got around to building my TMCC/Legacy Signal Booster kit. I have always had trouble with some TMCC Steam engines responding on my 15x25 home layout. This was somewhat unexpected although I have a lot of parallel tracks and tracks crossing over others. I just kind of muddled along with it.
Fast forward to York this Spring. Legacy just would not work on our modular layout in Purple Hall. I blamed it on the building wiring, and figured we were going to need to add a ground plane wire, or I could just build the Signal Booster kit.
The kit went together easily with GRJ’s excellent instructions and photos. So I was excited to hook it up to my home layout for a test. Power on. What?? The signal strength LED is red. With adjustment of the Signal Booster gain control it gets brighter, but it is still red. Have I had a bad Legacy base all along? At this point, as I am anticipating getting an RMA from Lionel, I decided to disconnect the Signal Booster from the track. Now I have a beautiful emerald green signal LED.
OK, now I have a layout problem. I pulled out the ohmeter and measured between the earth ground lead on the buffer and the outside rail. I got 7 Ohms. That’s not right! The layout is pretty much shorting out the Legacy signal. I am amazed that I had any control of my engines. (BTW, the Signal Booster worked so well, that by adding it, my engines responded flawlessly even with the signal mostly shorted out!)
Now started the hard work of finding the short. I do not have any ground plane wires. How is earth ground shorting to the outside rails?
I run Legacy and DCS. Track Power is from a Z4000, a Z1000 brick and a PH-180 brick feeding the TIU. My Legacy base is connected to an LCS WiFi module via the DB9 to PDI cable. The LCS wifi has a PDI cable connection to a Ser2 module which is daisy-chained to 6 ASC modules (TMCC) and 1 BPC module (not yet connected to track). The ASCs control Tortoise switch machines which are powered through diodes from the 14VAC Accessory terminals on the Z1000.
I re-connected the Signal Booster to the track (LED is red again) and one at a time starting with the Legacy base, I followed the problem down the daisy chain of connections:
Unplug DB9 cable from Legacy Base (green)
Unplug PDI from LCS to Ser2 (green)
Disconnect data wire to first ASC (still red)
Disconnect comm wire to first ASC (still red)
Disconnect A and U power connection to first ASC (green).
That’s it. The power leads from the 14VAC Accessory output on the Z1000 to the ASC relay contacts are shorting earth ground to the outside rail. To rectiify this, I moved the power leads to my Z4000 14VAC fixed accessory output and got a nice green light.
14VAC power leads circled in green:
I did verify that the ASC's U connection went to the Z1000 Common, and the ASC's A connection went to the Hot on the Z1000. I thought about reversing the connections, but the ASC manual specifically warns against doing this.
BTW, the Z1000 18VAC track output is phased with the other transformers (I did not check phasing with the 14VAC Accessory output). There must be some common connection in the Z1000 and/or the ASCs to cause this. I’ll leave that up to others to figure out, but at least I have a solution.
Here is a big Thank You to GRJ, not only for making the Signal Booster available to us, but also having the insight to add the signal strength LED feature. I would not have even thought of checking for a short from earth ground to my outside rail had it not been for the signal strength LED.
I’ll post Part II of this story in a few weeks when I use the Signal Booster on our modular layout at the York State Fair.
Bob
Cliff Notes:
1. The Signal Strength LED on the TMCC/Legacy Signal Booster is very useful.
2. If your TMCC/Legacy Signal is poor, check for continuity from earth ground to your outside rail. There shouldn't be any.
2. In my case, the power leads from the 14VAC Accessory output on the Z1000 to the ASC relay contacts are shorting earth ground to the outside rail.
