Greetings Blog Followers... While I am awaiting the arrival of my track I took the opportunity to run some of my older locomotives and discovered that an old favorite seemed to have lost some power. The locomotive in question is an Athearn SDP40 painted in the New Haven McGuinness livery. For the purists I know that the New Haven never had an SDP40. For the record the EMD SDP40 is similar to the EMD SD45 and the model sits on an SD45 frame. The easy to spot difference between the two is at the rear of the locomotive where the SDP40 has an extended long hood to accommodate a boiler. This particular Athearn model is at least 15 years old. It has the "newer" plastic side frames and gold colored motor with flywheels. Follow along as I inspect, locate and then repair the problem.
This is the unit with it's shell removed. Note the Kadee under set shank couplers (#47) with the plastic coupler box and screws. This is done to safe guard against any electrical shorts when connecting this locomotive back to back with another similar locomotive as the Athearn metal frame is grounded to the motor. Both couplers are exact fits with the Kadee coupler height gauge. If you are running consists of Athearn units with this type of electrical system this is the preferred coupler set up.
This view shows that the "Power Strap" has significantly rusted. The sliding electrical connection at the rear truck and head light strap are compromised This is/was a common problem for Athearn Blue Box fleet and is an easy fix.
A close up of the power strap and rear truck power contact. Not an ideal electrical connection.
A Close up pf the power strap and headlight connection.
Here is the motor with the power strap removed. The brass contact strip on type of the motor is clean and so are the truck contacts. This will make the job even easier. If you find on your locomotive(s) that the motor brass contact strip is extremely dirty and you need to remove it to clean it up use extreme caution as the motor brushes and springs are held in place by this power strip. If you have to wire brush or sandpaper the truck contacts uses extreme caution that you do not get any grit into the truck gears which are open at the top.
A pretty clean truck power strip
A clean front truck power strip and headlight power strip.
The parts required for an easy repair. Flexible wire and a shortened and cleaned power strap.
The power strap is cleaned and shortened. A copper flexible wire is cut to a approximate length and we are ready to prepare for soldering. Note that I am using 60/40 rosin core solder and rosin core flux. In soldering remember that flux is your friend and the flux capacitor makes time travel possible. All kidding aside the flux cleans the work surface and allows the solder to melt and flow at a lower temperature. The first step is to add some flux to the shortened power strap and the truck contact strips.The second step is to solder the flexible wire to the shortened power strap while it is off the motor. Leave enough wire at both ends to make contact with the truck power strips.Step three is to solder the wire to the truck power strips. Step four (see below) is to solder the headlight power strip to a separate wire that is attached to the shortened power strap.
Here is the completed job. Note the small separate wire that is attached to the headlight power strip. This is an important addition as it allows the wire to the front truck to remain flexible so the truck will easily negotiate curves and uneven track surfaces. Since the copper wire is bare you must make certain that is does not contact the flywheels which will cause a short. 
A top view of the finished job. Upon completion I cleaned the excess flux off with an alcohol pad. Since I had the alcohol pads out I used a another one to clean the motor armature.
A close up of the front truck and headlight wires. I used to just attach the headlight strap to the wire going to the front truck but learned the hard way that this causes the front truck to lose a lot of it's flexibility and leads to derailments. Going to this application has worked extremely well
The unit has been tested and then retested with it's shell on. The unit is now running extremely well and the head light is bright with no flickering. Remember these are old school units. They simple in design and construction and they are pretty easy to troubleshoot and repair. After a light lube this locomotive is ready for another 15 years of service.
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