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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.

2022-02-06 - Randall Repairs: Turnout T161

Category Randall


Turnout T161 (end of siding between Bridgeport & Sultan).


Intermittent loss of power on frog.

Summary Fix

Deactivate turnout (always straight). Bypass the frog polarity contact/inverted.

Description of Issue

Back in 2018, we had engines stop-and-go on turnout T161 for quite a while, especially steam engines, or short non-MU engines. The turnout was always in the normal position when this happened. Back then, it was determined the frog power routing on the Fulgurex created a resistance. This was solved in 2018-12-12 by replacing the Fulgurex. The issue re-appeared last year, and it was “fixed” by Allen spiking the frog in place. This worked for a while, and now the issue is reappearing again, with trains going dead on the frog.

Frog issue: Issue is frog power via the Fulgurex contacts. Last time, it was solved by swapping the Fulgurex. Eventually the contracts just oxidize or present some kind of resistance, likely to complete lack of use. And we cannot throw that turnout since the throw bar has been spiked.

Description of Fix

Since we have decided to not use the siding, the suggested attempt was to wire the frog directly to the proper polarity rail power, thus bypassing the Fulgurex altogether.

This is how the terminal block was initially wired:

The 3 top wires get power from the track (red and black) and then power the frog (green wire).

The bottom wires connect to the Fulgurex: green/yellow for turnout power/direction, and then black/red/green for the frog contact.

After rewiring the terminal block:

Changes made:

  • Top green wire (frog) is connected directly to red rail power (for straight running).
  • Bottom green/yellow wires are disconnected from the turnout power input and moved on unused terminals. This prevents us from throwing the turnout by accident.

This was done and the test train worked beautifully without a glitch.

This can be easily reversed:

  • Connect the top green wire to the middle position between red & black.
  • Connect the bottom green + yellow to the terminal positions 1 & 2 (left most).
  • Either replace the Fulgurex or clean the switch contacts.

Follow-up needed:

  • Some kind of label or tape on the turnout toggle on the panel to remember it is deactivated.
  • The other turnout to enter the siding is still working, so we could use this siding and back out if needed (unlikely as we see no traffic there).

Edit 2022-01-10: The problem is still not fixed. It worked that day, and a few days later, trains started stopping again on the turnout. At least now we know it’s not a frog issue, so it leads me to the next suspect, which is the power feed pickup. More on this later

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