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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.

2021-02-06 - Repair for Turnout T320

Category Randall

We’ve been experiencing some engines shorting on turnout T320 “again”. And interestingly, some engines would go past that turnout with no problem, and some would stop and short on the turnout.

A pair of SP SD40s arrive at T320.

It’s worth noting that this turnout is currently spiked. The tortoise is currently missing the spring wire, and there’s a short in the toggle button at the panel; because it offers little valuable operational benefit to us, I had thus disconnected it and spiked it for now.

Once I learned Jim was having issues there, my first reaction was try different trains to replicate the problem and identify some kind of pattern. Our track cleaning engine EMDX 1201 has no trouble going over it, nor do the automated trains. Maybe it’s a load issue… I tried to replicate the issue using two UP SD70s there with a long train, and could not replicate the problem. However once, just once, I got the 1201 engine to do a short stop-and-go hesitation there. Yet, very interestingly, the issue has been consistently reproducible with these SP SD40s, and I finally got to be on the spot to see the problem in action. I was eager to be able to reproduce it… not only is this turnout is really hard to reach making it nearly impossible to get the train out of it, it is also a very important part of the automation so I need trains to run flawlessly over it.

After trying some variations, I found these SP units work fine alone, yet they short when “under load”. And when shorted, here’s an interesting detail:

Clearly the front wheel of the leading truck is lifted just a tiny bit and shorts against the point which has the reverse polarity.

I also noticed the engine and the truck lifting a very itty tiny bit and then falling back down in that case. So clearly there is a geometry issue with the rails. The stock rails felt nice and level through the turnout. That left the inner point as a culprit, for example by not being closed properly, it can be enough to lift the front wheel, or make it bind in some sort. And voilà, that’s the case here.

The annoying thing is that this turnout is really hard to reach. However by taking a picture from the top, I was able to notice the inner point does indeed not close properly against the stock rail. After removing the spike, I moved the points and saw that the bar under the point has a tiny piece of metal that is bent and was preventing it from closing properly. I carefully bent it back and now it closes perfectly, and I respiked it so that it would not move.

This is obviously just a band aid -- that turnout is still missing its tortoise spring, and the toggle button still shorts… to be fixed “later”, right now it’s at the bottom of my long list of fixes needed on the layout. Yet sometimes simple temporary patches and quick fixes are just as satisfactory.

After this, I tried the SP train a few times over that switch and it worked like a charm.

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