This installation is for a HO Scale Ahearn GP38-2 Early Version using a TCS WOW121-Diesel Decoder, RTR-MB1 Motherboard with built in Keep Alive®
and UNIV-SH4-C WOWSpeaker kit.

This was performed by our friends from DCC Xpress installations.
They offer high quality WOWSound installations for a flat rate complete with free return shipping!
You can find them at:

These items are available in the WDK-ATH-10 which was used for this installation.
RTR-MB1 Motherboard with Keep Alive™ WOW121-Diesel Decoder UNIV-SH4-C Speaker Kit
Click here for more information on the WDK-ATH-10 and the rest of the WOWDiesel Kits line.

Important Soldering Tip:
Please do not use any flux either liquid or paste on the mother board. It will damage it. Use only Rosin core solder approved for electronics use.
We recommend to use only Kester "44" rosin core, SN63PB37, .015" diameter, part number 24-6337-0007.
This can be ordered from Techni-Tool under Techni-Tool part number 488SO157

HO-Scale Ahearn GP38-2 Early Version shown prior to installation.

    To start off this install, we must first release the front and rear tabs on the frame bottom as highlighted above in red.
With these released, while gently pulling upwards along each side of the frame, lift the shell off of the frame.
Take care to release the handrails as you lift off the shell so they don't break.

The Ahearn GP38-2 Early Version shown with the shell off. Remove the wires from the original lighting board and remove it from the chassis.

The RTR-MB1 has a motor pick up clip pre-attatched to the bottom, so mounting it onto the locomotive could not be easier.

Clip the RTR-MB1 to the frame and solder the motor and track pickup wires according to the included wiring diagram.
When attaching the wires to the pads, it is not necessary to insert the wires through the holes. We recommend attaching the wires flat on top of the solder pads


In this installation, we replaced the original 1.5v bulbs with LEDs using a small dab of hot melt glue to secure the front and rear LEDs to the shell as shown above.
With the 25mm X 14mm WOWSound speaker inserted into the UNI-SH4-C enclosure, mount this assembly to the shell as shown with double sided foam tape.

If your speaker enclosure installation covers the portholes on the enclosure, we recommend adding new port hole(s) similar to the original porting. Be sure that the new portholes are the same size and amount of the original and are vented freely into the locomotive We have found introducing a port of the correct size greatly increases the volume and sound quality of the installation. Too much or too little porting decreases the sound quality.

We have found that LED light output is brightest when shinning directly into the end of the light tube, but in some circumstances they may be placed along the length
of the tube as well with satisfactory results. In doing so, white light LED output would be least affected, while non white LED output will be more affected by placement.

TCS motherboards include on board current limit resistors for LED use. There is no need to apply external resistors for LED use. 

The RTR-MB1 and GEN-MB1 have on board 1.5volt power supplies to conveniently power all the original 1.5volt bulbs that come with your Athearn locomotive. The front headlight and rear light pads are configured for 1.5volt use. Additional 1.5volt pads are available for other connections for ditch lights etc. If you prefer to use LED lighting as an option, there are LED solder connection pads. Current limit resistors are built into the board so no external resistor are needed for LED use.


To allow for space to ensure the proper clearance for the decoder installation, there is a section of shell and a weight that must be trimmed.
This is located inside the removable top piece of the shell. With this piece removed, trim back the shell top as shown above, along with trimming
the weight approximately 1/2".

Reinstall the weight into this cavity and reattach the piece to the top of the shell.

With the shell top complete, solder the speaker and LED lighting wire leads to the RTR-MB1 according to the included wiring diagram.

You can now plug in your WOW121 decoder.

Lastly, in order to keep the wires neat and prevent possible shorts, lace the wires into a bundle using lacing cord, which is a wax impregnated string 
used for wire bundling and making harnesses. There are many choices of lacing cord available from Digikey
We use part number 802534B BK032-ND

Now you can close up the locomotive and reinstall the coupler assemblies. Be sure to be mindful of wire routing and reassembly of the shell as to not damage 
or foul the installation. Your Ahearn GP38-2 Early Version is now WOWSound equipped and ready to roll!

Other solder tips: When stripping wire, only strip a tiny little bit of the insulation. Strip no more then a 1/64 of an inch. When the wire gets tinned with solder the insulation will shrink back more. Try to not expose any more wire then half the length of the solder pad at most. In no case should solder or exposed wire wire ever be outside the boundary of the the solder pad you are attaching a wire to.
Click here for important information on properly Stripping and Tinning wire

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