Recently I was asked to replace an existing installation of a Digitrax DN121 decoder with a new Lenz Silver Mini. The PC board had been removed from the locomotive. So this post will show a different method to install a decoder in this loco that was not available in a DCC version and that no after market decoder board has ever been offered for.
For that reason I felt there would be an advantage to having the LED's and resistors mounted on a board of some type.
I aligned the board so that the front LED is at an equal distance from the front of the frame as on a stock Athearn F59PHI. The black line across the board and saddle mark this alignment.
Notice in the photo above that the little bars on the motor saddle that go across the motor contact wipers on the stock mechanism are gone on the saddle we are using. This had been removed in the original DN121 installation. If the loco you are working with is a new installation, this should also be cut. Too see this step refer again back to the earlier post on this model.
The polarity of the front LED is reversed so that the anodes of both LED's will be tied together.
The white, yellow, and blue wires are soldered to the board as shown in this photo and the other wires are trimmed to 2 inches in length. Keeping them long will make it easier to put things back together.
Several areas to to watch out for are pointed out.