The larger SG passenger cars such as the 418 series, Blue Comet, and state cars employ a contact roller assembly which consists of a fiberboard insulator, a tensionor spring, and a metal bracket with bent tabs that actually holds the roller itself. Occasionally, and without warning, the metal bracket assembly will come loose from the fiberboard mount, thus releasing the tensionor spring which falls between the tinplate rails, while the aforementioned bracket with its attached "hot" wire grounds out and creates a short. Since I employ Z-4000's on both layouts (along with QSI Powerguards), the nanosecond breaker kicks in before any damage is done. The spring is usually undamaged and can easily be found between the rails, and is reusable.
The key to the repair is to slightly crimp the metal bracket assembly so that it fits more securely on the fiberboard mount. The tensionor spring must also be properly centered as the metal bracket tabs are secured to the fiberboard. Pushing down on the contact roller to test the spring tension/alignment completes the repair. Once this repair is successfully accomplished, there should be no further problems.
Checking EACH contact roller assembly to see if the mounting bracket is properly attached to the fiberboard WITHOUT too much lateral play will insure no further problems.
