A long time customer and a professional decoder installer Latham S. explains how to fix chronic pickup problems with Athearn Genesis series HO locomotives. Thank you Latham for taking the time to document your solution.
Athearn Genesis F7 Intermittent Power Loss Repair
A problem existed with my Athearn Genesis F7 units and after some analysis effort I have found a way to correct it.
Due to the commonality of design many Athearn Genesis diesels may reflect the same symptoms. This problem exists with DCC decoder installations since DCC is more discriminating about power interruptions.
The problem is in the truck design itself and is caused in part by lateral travel of the wheel axle which has a a large chamfer on the ournal bearing end which loses contact when moving out of range of the contact plate. Another component exists because the side frame containing the contact plate is precisely molded in place and centered in the wheel journal which is 0.060 in inside diameter to a mating wheel shaft outside diameter of 0.057 leaving a deficit of 0.003 between diameters. Simply put precise allignment of axes means no contact is possible.
The system works because the gear box clearances are lose enough to allow gravity to slightly misalign the axis between wheel axle and journal bearing making contact with the contact plate albeit intermittent. Note the side frame is mechanically and rigidly attached to the gearbox which prevents the contact plate from floating on the axle to make contact.
Solution: Reduce lateral side travel and ensure electrical circuit with contact plate:
This was accomplished by increasing the journal wheel shaft length by 0.030 that limits and reduces lateral travel and adding a very small amount of Aristo-Electrolub to the journal bearing cavity to ensure electrical continuity with the wheel. The Northwest Shortline Wheel #37291-4 has the correct length shaft and replaces the Athearn wheel.
The attached drawing offers the proceedure used to correct the problem I experienced after installing a QSI Titan Sound Decoder.
The engine has been tested and is running as it should with great sound!