# Athearn F7A Decoder Install



## Stumpy (Mar 19, 2013)

Athearn F7A. _Not_ DCC ready.










Diagram from HO Seeker.


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## Stumpy (Mar 19, 2013)

Above the fuel tank pry the sides of the shell out a bit and lift the shell off of the tabs on the chassis.











Remove this screw on each side to the lift the weight straight up and off.











These parts will be removed next.











Remove the small clip (green arrow) that connects the wiper clip for the light to the connector clip (red arrow/lines). Remove the connector clip.











Remove wiper clip for the light (red arrow), plastic bulb retainer clip (green arrow) and the light bulb. Leave the light bracket in place.











With all of the above removed..


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## Stumpy (Mar 19, 2013)

Remove the four motor mount screws from the bottom of the fuel tank. Then remove the motor.


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## Stumpy (Mar 19, 2013)

These clips from the top and bottom of the motor serve as the power pickup and retain the motor brushes and brush springs. Remove them being careful to keep the brush springs from launching into the stratosphere.



















Clips, motor brushes and brush springs removed.


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## Stumpy (Mar 19, 2013)

These tabs on the clip from the bottom of the motor contact the bare metal channel in the chassis below the motor to pick up power. The motor gets (-) power from the chassis.




















Since the motor will be getting power (+/-) from the decoder, we need to isolate the motor from the chassis. The tabs on the clip can either be removed or hammered back flush with the rest of the clip. I removed and filed flush.











Then cover the bare channel in the chassis with electrical tape.


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## Stumpy (Mar 19, 2013)

Solder two 6” wires to the risers coming from the right side of each truck. This is where the decoder will get (+) power from. These wires will be connected to the black wire on the decoder.

Note: Everything that gets soldered gets a generous application of paste flux.


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## Stumpy (Mar 19, 2013)

The decoder and wiring diagram. I've had good luck so far with these "Z" decoders. The tiny size is a big plus in non-DCC ready applications.

Note: Since I wasn’t paying attention  I reversed the black & red wires supplying power to the decoder, so I also reversed the orange and gray wires supplying power to the motor.


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## Stumpy (Mar 19, 2013)

The LED lamp to be installed.

Wire stripper tool that will actually work on the tiny decoder wires.

Tape used to secure wires.


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## Stumpy (Mar 19, 2013)

Solder the orange wire from the decoder to the bottom motor clip and the gray wire to the top motor clip. 

A “helping hands” tool comes in very handy here.




















Reinstall the motor brushes, brush springs and clips on the motor.


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## Stumpy (Mar 19, 2013)

Thread the light bulb wires through the hole in the light bracket, secure with high temp tape, then reinstall the bulb retainer clip.











Reinstall the motor.











Thread the decoder & wires through one of the holes at the rear of the weight and reinstall the weight.











We still need to get power from the chassis to the decoder. So, wrap the red wire around one of the screws that secures the weight.


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## Stumpy (Mar 19, 2013)

Trim the leads from the light appropriately and attach to the white & blue wires on the decoder. For this installation the black light wire must be attached to the white decoder wire and the red light wire must be attached to the blue decoder wire. If not the light will not work.

Shrink tube all soldered wire connections.

Using the tape, secure the wires along the side of the weight so they won’t interfere with reinstalling the shell.




















Then secure the decoder to the “nose” on the back of the weight.

Although that ultra-thin, high temp tape can be a bear to work with, the tape job isn't really as bad as it looks in the pics.


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## Stumpy (Mar 19, 2013)

On track.

Above I mentioned I reversed the power leads to and from the decoder. So, with the throttle set forward the loco runs backwards. Setting CV29 to reverse direction of travel will be much easier than a do-over.


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## flyboy2610 (Jan 20, 2010)

Nice install! Nice tutorial, too!


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## kilowatt62 (Aug 18, 2019)

Nice job man. Great tutorial as well. Answered a few questions in back of my mind for future projects. 
I have tooling questions! Lol. 
From where did you get the wire strippers, tape, and LED’s from please. You happen to know the diameter of the LED’s?


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## Dennis461 (Jan 5, 2018)

That looks like a newer Athearn.
I put the LED in the top shell glued into the bulb spot, to prevent lighting up the cab. A micro 2-pin connector allows disconnecting the LED when removing the shell.


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## Stumpy (Mar 19, 2013)

kilowatt62 said:


> From where did you get the wire strippers, tape, and LED’s from please. You happen to know the diameter of the LED’s?


Wire strippers.









Eclipse Tools CP-301G Pro'sKit Precision Wire Stripper, 30-20 AWG: Amazon.com: Tools & Home Improvement


Eclipse Tools CP-301G Pro'sKit Precision Wire Stripper, 30-20 AWG: Amazon.com: Tools & Home Improvement



smile.amazon.com





Tape.









High Temp Tape, ELEGOO 4 Pack Polyimide High Temperature Resistant Tape Multi-Sized Value Bundle 1/8’’, 1/4’’, 1/2’’, 1’’ with Silicone Adhesive for Masking, Soldering etc.: Amazon.com: Industrial & Scientific


High Temp Tape, ELEGOO 4 Pack Polyimide High Temperature Resistant Tape Multi-Sized Value Bundle 1/8’’, 1/4’’, 1/2’’, 1’’ with Silicone Adhesive for Masking, Soldering etc.: Amazon.com: Industrial & Scientific



smile.amazon.com





LEDs









20 x Pre-Wired 5mm warm white lighting LEDs prewired resistor for 12V/16V DC | eBay


Price for 20 prewired 5mm LEDs warm white light. prewired 1K resistors for 9V to 16V DC use. 20 Complete prewired LEDs. Emitting color: warm white. Add to Favourites. for easy wiring, you may buy a distribution board and light them up easily.



www.ebay.com


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## kilowatt62 (Aug 18, 2019)

Stumpy, 
You're awesome man. Thanks for taking the time to post the links. Mucho grassyass! 😉


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