S-Helper Service F3

Operator's Manual

We don't have a digital copy of the F3 operator's manual available, but the F7's manual, available here, covers most of it. Don Thompson says the main difference is in the layout of the main printed-circuit board for the F7. The F7 has LED classification lights, so the pin assignment is different. So, use that manual, but be sure to look at the photos and diagrams further down this page for the actual F3 circuit boards, if that is of interest to you.


This model won the "S Scale Locomotive of the Year" in 2001, as voted on by the readers of Model Railroader magazine.

Product Review

Bob Hogan did a product review of these engines in the November/December, 2001 issue of the S Gaugian magazine.

MU Cables

MU cables between these engines only synchronize the motor current; they have no effect on the sound of the engines.


Don Thompson warns to not plug DCC decoders into this engine without dealing with the headlights first. The headlights are 5-volt bulbs, and they will blow as soon as the decoder receives power (usually around 12 volts). One option is to consider replacing them with LEDs and a matching resistor. The same applies to class lights, numberboards, and Mars lights, as applicable.

For the dual-headlight models, Rich Gajnak provides the following information. These engines have bracketing to both lights on the cab interior casting. Note that both the SHS and MTH models are the same, except that the SHS models use lightbulbs (see note above) and MTH's have LEDs. These models have the active headlight in the upper opening regardless of whether it is a single- or double-light version. Real-world F units have the MARS light (when so equipped) in the upper opening and the headlight in the door. For the SHS F units the lights are wired to different pins on the 8-pin DCC plug. Rich swapped the lights at the cab interior casting on his models.

SHS F3; photo copyright © Rich Gajnak; used by permission


Don Thompson says that to remove the shell, remove the four corner screws, and then wiggle the shell. Put a small screwdriver through the back door on the top of the floor to release the rear of the shell first.

Follow the link to see how to disassemble the engine's trucks. The F3 is done the same way as the NW2; see this web site: How to disassemble SHS trucks.

LocoMatic Sound

This board is for the F3 A-unit, with LocoMatic, either AC or DC power, with sound (part #01200).

LocoMatic to DC Conversion

Converting one or more engines with LocoMatic factory-installed to a plain DC version requires the removal of the LocoMatic unit and adding a DC-shorting plug to each of the engines. The MU cables are then no longer needed. Test each unit individually for proper starting direction (if running in a multiple-unit consist).

LocoMatic to DCC Conversion

Converting these engines with LocoMatic factory-installed to DCC, S-Helper Service used the QSI Revolution U F3A decoder. It provides the slightly higher power that the engine needed, and it also supported the 5-volt supply for the lights.

DCC to LocoMatic Conversion

To do this conversion, you must use the LocoMatic board specific to the F3. Do not use the LocoMatic board of an F7, as they are not the same.

For multiple-units (MU) hook-ups, you will need two sets of MU cables to connect between the engines. An alternative to the MU cables is to find an F3 LocoMatic board for each engine in the consist. Don Thompson recommends only using the Dallee 10-button Controller, because otherwise operation of the engines is not ideal. His advice is that, since these parts were created around the year 2000, it might be cheaper and easier to buy a DCC system than to try to find the LocoMatic boards, unless you already have them.

Printed-circuit Boards

This circuit board is for the F3 A- and B-unit, with DC power, non-sound version (part #661-X004R1).

This photo shows the above-mentioned circuit board installed:

The next photo is of the F3 A- and B-unit DC shorting plug. These should only ever be used for S-Helper Service F3 engines, otherwise an engine can be damaged.

(photo © Roger Nulton)

Soundtraxx Tsunami Sound Decoders

The original sound decoders were manufactured by Soundtraxx. Don notes that these boards had two tiny circuit-breakers that would be triggered any time more than 12 volts was applied to them, and they would require a reset by Soundtraxx.

This document, provided by Don Thompson, lists the Soundtraxx Tsunami CV settings with which the models were configured.

This is an external link about how to use the sound decoder.

The next diagram shows the circuit board layout of the board that S-Helper Service installed in their F3 (only) models that were using the Soundtraxx Tsunami DCC decoder. This diagram shows how the various wires are to be connected. This version is for the models that have Mars lights.

The next diagram is the same as above, except that this version is for the models that did not have Mars lights.

QSI Revolution Sound Decoders

Later, S-Helper Service started using the QSI Revolution sound decoders, due to the current-draw that maxed out what the Tsunami could handle. The diagram below is from the QSI document.

QSI DCC Installation Document

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