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The Randall Museum in San Francisco hosts a large HO-scale model model railroad. Created by the Golden Gate Model Railroad Club starting in 1961, the layout was donated to the Museum in 2015. Since then I have started automatizing trains running on the layout. I am also the model railroad maintainer. This blog describes various updates on the Randall project and I maintain a separate blog for all my electronics not directly related to Randall.

2021-01-02 - Front Yard toggles on Mountain and Valley Panel

Category Randall

The Mountain Turnout Panel has this little mysterious “Front Yard” toggle at the bottom, and for a long while I could not understand what it was connected to nor what is purpose was:

Now I understand that flipping it right or left connect its output to the Mountain 1 or Mountain 2 panels power:

There is a similar looking “Front Yard” toggle on the Valley panel:

And that one I know is also connected to the Stockton Yard panel via a 3-position toggle with a “Valley” position:

I had noticed in the past that tentatively throwing these toggles would mysteriously short parts of the layout. It also means power is drawn from the wrong booster.

However, back in a DC-designed layout, what could have been their purpose?

In DC, power applied to the rails directly dictates the speed and direction of the trains. When crossing power districts, it’s essential to have an interchange track: power it from the incoming power district, move the train into the interchange track, then toggle power to the outcoming power district.

That’s why there’s a power selector on each of the two bottom yellow tracks on the Stockton Yard panel: one can select whether power comes from the valley (to enter the yard), or from the mountain side (to exit the yard), or from a local DC cab throttle specific to the yard (to enter and exit the yard tracks):

  • When the Stockton Yard power selector is on “V”, power is selected from either Valley 1 or Valley 2 using the “Front Yard” toggle on the Valley panel. It’s a 3-position toggle, and the middle one is unused, leaving the wire unconnected.
  • When the Stockton Yard power selector is on “M”, power is selected from either Mountain 1 or Mountain 2 using the “Front Yard” toggle on the Mountain panel. It’s a 3-position toggle, and the middle one is unused, leaving the wire unconnected.
  • When the Stockton Yard power selector is on “Y”, power used to come from the local DC throttle, which is now connected to the yard’s DCC power district.

As part of a DCC only setup, all this can be removed.

The M/Y/V power selectors on the Stockton Yard panel are particularly error prone. For example for a while we had them set to V, and the Front Yard selector on the Valley panel was set to 2. This basically powered the yard using the booster and power district for Valley 2. The consequence was that any short in the yard would also short the mainline served by Valley 2. It took some effort to figure this relation out as it was far from obvious.

Eventually I may remove both Front Yard toggles, the track power selectors, and all the wiring in between.

In the meantime I can unsolder the power selectors inputs to make sure we have only the proper choice available and render the toggles moot and inoffensive.


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