Installation of Loksound decoder in Athearn SD70M

Loksound Installation – Precision Craft Big Boy
Kit Revised 02-4-2009
Introduction
This kit installs LokSound 3.5 into the Precision Craft Models Big Boy. The kit upgrades the
non-sound Big Boy to be identical to the released factory sound model.|
The PCM Big Boy sound file loaded into the decoder has been edited to improve the bell and
change the whistle to the low base whistle of the large articulated Big Boy.
Figure 1 – PCM Big Boy
The Upgrade Kit
Figure 2 – The Upgrade Kit
The upgrade kit consists of:
• One LokSound MTC-21 pin decoder
• Two 100 Ohm speakers
• 2 Pin JST connector for speakers (Plugs into the PCM circuit board in the tender)
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Installation
Figure 3 - Installed Kit
1. Remove the tender shell by removing the 4 screws located at the four corners of the
tender floor. Remove the rear coupler and lift the tender shell off the frame.
2. Uninstall the smoke unit jumper located on the circuit board. Removing the jumper
will disable the manual DC smoke switch and enable decoder control of the smoke
unit. The jumper can be left attached to one pin or totally removed.
3. Remove the circuit board from the mount by unscrewing the mounting screw located
at lower left corner of the board. It also holds the smoke switch panel. Move the
board aside, it will still be connected to the harness and backup light.
4. Remove the speaker retaining frame, located under the circuit board, by unscrewing
the two screws located in the center of the frame.
5. Place the two speakers from the kit in their mounts as shown in Figure 4. Run the
wires connecting the two speakers as shown to avoid pinching them between the
speaker and the frame.
Figure 4 – Speaker Placement
6. Reinstall the frame. Run the speaker wire with the connector up through the slot in
the middle of the speaker retaining frame.
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Figure 5 – Speaker and Retaining Frame Installation
7. Reinstall the circuit board and connect the JST 2 pin connector to the open header
on the board. See figure 3.
8. Install the 21 pin MTC Loksound decoder. When you install the decoder, you may
need to reposition the large capacitor and flatten the leads. Be sure any bare
capacitor leads do not touch each or the decoder. Install the decoder with the black
connector up. It is keyed to prevent improper installation. Figure 3 shows the
correct installation
9. Reinstall the tender shell and test the locomotive.
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