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Upgrade MTH SP AC-6 Cab Forward Page 1 of 2

This 20-3025-1 Southern Pacific AC-6 Cab Forward was listed in the MTH 1998 Volume 1 Catalog.  When it died it was an excellent candidate for a PS2 Upgrade.  It's a little confusing to run.

Cab Forward Title

The upgrade was done in April 2012 using a MTH PS2 Upgrade Kit with the included Steam Locomotive Upgrade Kit Installation Manual - 4th Edition.  The page numbers refer to the pages in that manual.  When following the Installation Manual the color illustrations in the website manual are helpful.

 Step by Step Conversion Process

Tips - For a better grip, a big handled screwdriver is essential for loosening and tightening screws.  Wire management is critical. Keep in mind from start to finish. This PS1 Cab Forward was toast because factory had cut power wire insulation with a metal hold down strap.
  Be sure all retained components and wiring is sound.

Tender - Mount Circuit Board

Charge the 3V battery and use it to test lights, smoke fan, smoke heater, etc. before installation.
Plan the installation and do all drilling and grinding before installing the PS2 board. Remove the old battery stickum.

P. 10-13 Mounting the PS2 Board - The tender is too narrow for angle mounting or side mounting. The metal heat sink bracket must be mounted on the end of the circuit board.

Cut off the mounting bracket tab.  Trim the heat sink bracket with the MotoTool cutoff wheel so it clears rectifier prongs when it slips on the end.
Tender Heat Sink 1 Tender Heat Sink 2
To fit heat sink bracket to the bridge rectifier, enlarge the rectifier hole with a Dremel cutting tool (a drill bit grabs and shatters rectifier). While grinding, protect PS2 board with a mask.  Hold rectifier top gently with vise grips. For mounting the heat sink bracket use a flat head machine screw for clearance.  The photo shows a 8/32 FHMS because I stripped the 6/32 threads in the heat sink bracket.
Tender Heat Sink 3 Tender Heat Sink 4
Chassis Mounting Holes
The heat sink bracket will be mounted on the original heat sink to clear speaker.  Cut a stand-off for mounting the other end of the PS2 board bracket. (I used scrap black plastic pipe.) The speaker top is 11/16" off the tender chassis.  One hole is added to tender front for mounting bracket.

Tender Chassis Layout

Tender Holes Drawings

P. 20 Installing the Battery and Volume Pot - Charger Socket - Cut the rectangular hole for the charger by drilling two holes and shaping with grinding wheel and file.  This is easier with sharp files and new grinding wheels.

Tender Chassis Holes Drilled

Move the original smoke on/off switch from the Boiler to the Tender for the switch plate.

P. 20 Installing the Battery and Volume Pot - Charger Socket - Test charger plug in the installed socket for fit. The socket is easily squished if hole is too small. Tender Charger Socket

P. 19 Wire and install speaker before the PS2 Board is installed.

Tender Speaker


Tender Board Mounted

Tender - Install Wiring Harness

After the PS2 Board and speaker are installed, the tender harness must be threaded through the shell entry hole from the outside (never to be parted from the shell again).

Tender Harness Inserted Tender Harness Left
Wire the volume pot before reinstalling in the original position.  The chassis front bracket opening for the wire harness strain relief must be enlarged for the PS2 larger harness. (Use MotoTool)  The bracket enhances wire management.

Tender Wiring Right

P. 14 The plastic insulator EE (for coupler) isn't needed for this installation.  P. 17 The 8 PIN socket is unused.

Tender Wired Left Side

The kit battery is installed in the original battery location.

Tender Wired Right

Continue to Page 2 and Boiler

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