LW transformer has me stumped

I've overhauled about a dozen or more LW transformers including a whistle diode upgrade but this one has me stumped. I have fixed voltage from the C and B posts, variable voltage to about twenty volts from the U post, the fixed posts will move a locomotive but the variable post won't move a locomotive. Can't find anything loose or a poor solder point. 

Original Post

That is a good one... Have you measured the voltage WITH the locomotive connected up? If you were reading the voltage with no load, it would be possible to get the ~20VAC, but then with a load, that voltage could plummet through a high resistance link.

You are connecting A-U correct?  I would carefully check the internal wiring. If you have to remove the top from the base, wires have to be disconnected. It would be possible for someone in the past who may have worked on it to cross two wires reassembling.

Does the light on the handle change when you move the handle?

ADCX Rob posted:

Circuit breaker is open. It will read full voltages w/o a load.

The bulb filament would be a high resistance link as previously mentioned. A test for this particular condition would be to test the voltage between A and U with the bulb removed.

Take a look at the direction control tab and contact on the fiber board. The tab had lost its spring tension and was making poor contact on the fiber board contact. The contact on the board was also burnt. Bent the tab up, bent the contact on the board down and cleaned up the contacts with a file. Working good now.IMG_7614


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