M.T.H. SD70MAC User manual

R
ELECTRIC TRAINS
MTH SD70MAC DIESEL ENGINE
OPERATING INSTRUCTIONS
Thank you for purchasing the MTH Electric Trains SD70MAC diesel
locomotive. Despite its scale size, the locomotive is capable of operating
on O-31 3-rail track with any compatible AC transformer, (see page 32 for a
complete list of compatible transformers and wiring instructions) and is
completely compatible with most other 3-rail locomotives, rolling stock and
accessories.
The locomotive is equipped with several deluxe features that are simple
and fun to operate. Each feature is described among the following pages
which should be read before the engine is operated. For those of you who
can’t wait to get started, the Quick Start Operating Instructions, found on
page 3, should be read so that you understand the basics of the operating
system. Please note that some features are only found in the Proto-Sound®
equipped engines and are marked as such.

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MTH SD70MAC Operating Instructions
Table Of Contents
QUICK START - BASIC OPERATION(All 3-Rail Models) 3
PROTOSMOKE™ UNIT OPERATION 4
PROTO-SOUND® OPERATINGINSTRUCTIONS 5
Proto-Sound® DCRU® Reverse Unit Operation (All 3-Rail Models) 5
Horn Operation 6
Bell Operation 6
ProtoCoupler™ Operation 7
Cab Chatter Sounds 8
Squeaking Brake Sounds 8
Tips On Using The Squeaking Brake Sounds 9
Freight Yard Sounds (FYS) 10
Quick Overview On Activating and Triggering Freight Yard Sounds 10
Tips On Using FYS Features 15
Self-Charging Battery Backup System 17
Replacing The Proto-Sound® Battery 17
Proto-Sound® Volume Adjustment 18
USING “RESET" TO PROGRAM PROTO-SOUND® 19
Entering RESET Options 19
Setting The Engine Volume 20
Programming For Squeaking Brake Operation 20
Programming For Horn In Neutral Operation 21
Programming For ProtoCoupler™ Operation 21
Programming For FYS Operation 22
Activating Remote Lockout Control 23
ResettingAll Proto-Sound® Options To Factory Default 23
OIL & LUBRICATION INSTRUCTIONS 24
TRACTION TIRE REPLACEMENT INSTRUCTIONS 25
LIGHT BULB REMOVAL & REPLACEMENT 26
TROUBLE SHOOTING PROTO-SOUND® PROBLEMS 27
Proto-Sound® RESET Feature Chart 31
Transformer Wiring Chart 32
O-31 OPERATION 33
SERVICE AND WARRANTY INFORMATION 36
HOW TO GET SERVICE 36
LIMITED ONE YEAR WARRANTY 36

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MTH SD70MAC Operating Instructions
QUICK START - BASIC OPERATION
The MTH SD70MAC contains state-of-the art electronics with several
built-in automatic features for incredibly realistic operation. Despite these
advanced features, the SD70MAC is easy to operate with any compatible
standard AC transformer (see the compatibility chart on page 32). All
models are equipped with an operating smoke system that should be primed
with smoke fluid before operating. Adding 20 - 25 drops of fluid through
the smoke stack should be sufficient. If you choose to not prime the units
with fluid, turn the smoke unit switch located under the trailing truck to
theOFFposition. (See Figure 1) This will prevent any damage from
occurring to the smoke unit when running the engine without a primed
smoke unit. For more information see the section on page 4 on Smoke Unit
operation.
The SD70MAC model is controlled by
aProto-Sound®DCRU® electronic
reverse unit. The reverse unit operates
in the same manner that all reverse units
function by using forward, neutral and
reverse states that are entered each time
the throttle is turned on and off or by
using the transformer direction switch (if
so equipped).
The reverse unit is designed to ignore
dirty track, dead spots on switches or minor short circuits without disrupting
the engine operation, even at slow, prototypical speeds. Once the engine is
placed on the track, the transformer throttle can be advanced. You will see
that only the engine’s lights come on and two dings from the sound system
will chime followed by the air compressor pump sounds. The engine does
not run. This is known as the RESET (see figure 2) state and is explained in
more detail beginning on Page 5. The Proto-Sound® DCRU® will not
power the motor until the throttle is turned OFF and then ON again. At this
point, the engine will now function just like any other electronic or
mechanical E-unit.
SmokeUnitSwitch
Figure 1: Locating the Smoke Unit Switches on
each A Unit
RESET
Neutral
Reverse
Neutral
Forward
Figure 2: ProtoSound® DCRU® Cycle Phases

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MTH SD70MAC Operating Instructions
PROTOSMOKE™ UNIT OPERATION
The SD70MAC contains a self-powered smoke unit that outputs a steady stream of smoke
through the smoke stack on the roof of the engine. The ON/OFF switch located next to the
power truck must be in the ON position in order for the smoke unit to function. See Fig. 1 on
page 3.
The smoke unit is essentially a small heating element and wick which soaks up and then
“cooks" a mineral oil-based fluid that omits a harmless smoke. The smoke is then forced out
of the stack via a small electric fan which runs at a constant speed. However, the smoke
intensity can be varied by increasing the transformer voltage setting. The higher the setting,
the more intense the smoke output.
For best results, we recommend that you add 20 - 25 drops of ProtoSmoke™, Seuthe, LGB or
LVTS fluid before you run the engine. If you don’t choose to add the fluid, then the smoke
unit switch should be turned off. Failure to either add the fluid or turn the switch off could
lead to damage to the smoke unit heating element and or wicking. Add the fluid through the
smoke stack hole. After adding the fluid, gently blow into the stack to eliminate any air
bubbles. Do not overfill the unit as overfilling can cause the fluid to leak out and coat the
interior engine components. When the smoke output begins to diminish while running the
engine, an additional 20-25 drops of smoke fluid should be added or the smoke unit switch
should be turned off. When storing the engine for long periods of time, you may want to add at
least 20 drops of fluid to keep the wick soaked with fluid and prevent it from drying out. After
removing the engine from storage, it is advisable to add another 25 drops of fluid, letting the
wick soak up the fluid for 15 minutes prior to operation.
SMOKE UNIT MAINTENANCE
CAUTION: Operating the engine without smoke fluid and with the smoke unit switch in the
ON position can damage your smoke unit wick, causing the wick to become hard, blackened
and unabsorbant around the heating element. When this occurs, it may be difficult for the wick
to soak up the smoke fluid resulting in poor or
no smoke output. If that occurs, we
recommend that you inspect and/or replace the
wick taking care to not run the engine without
fluid in the future. You can inspect the wick to
see if it needs replacement by removing the
smoke unit circuit board from the smoke unit
body as seen in Fig.2. After removing the
circuit board screws lift the circuit board away
and inspect the wick. If the wick is darkly
discolored and hard, it should be replaced.
Remove Circuit
Board Screws
Lift Circuit
BoardAwayTo
Reveal Smoke Wick
Figure 2: Inspecting The Smoke Unit

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MTH SD70MAC Operating Instructions
PROTO-SOUND® INSTRUCTIONS
The MTH ProtoSound® digital sound and train control system provides
the operator with unprecedented realistic operation on your model railroad.
In addition to actual diesel engine, CD-equivalent 16-bit digital sounds,
you get the following features:
1. ∗Built-In ProtoSound® DCRU® Reverse Unit * Authentic Diesel Horn Sound*
Authentic Diesel Bell Sound* Squeaking Brake Sound* Freight Yard Sounds*
Operating Remote Controlled ProtoCoupler™* Self-Charging Battery Back-Up
System With Automatic Battery Shut-Off* Remotely Controlled Reverse Unit
Lock-Out* Remotely Adjustable Diesel Engine Volume* Authentic Cab Chatter
Neutral Sounds* Authentic Diesel Engine Startup & Shutdown Sounds *
Each feature is described among the following pages. Though the system
is easy to use, we encourage you to read the instructions thoroughly.
PROTO-SOUND® DCRU® REVERSE UNIT
As mentioned in the Basic Operating section, the engine is controlled by a
DCRU® reverse unit that contains the standard forward-neutral-reverse
states found on most reverse units. However, as described earlier, when
power is first applied to the track, the reverse unit begins in RESET or what
seems like a neutral state. Power must be interrupted again to get the
locomotive to enter the forward state. It is this first RESET state that gives
ProtoSound® its unique, remote controlled functions. The system will enter
RESET whenever power to the track is off for three or more seconds.
NEUTRAL will be referred to as the state between Forward and Reverse.
ProtoSound® is equipped with a microprocessor, that, depending on the
amount of memory it is allotted, allows the user to utilize several remotely
activated functions. In the simplest terms, Proto-Sound® has its own
“Computer" controlling these functions. In fact, the power of this
microprocessor is the same as that of a 286 desktop computer! In order to
access many of these remotely controlled functions, the user must be in the
RESET state to do so. RESET is entered anytime power to the locomotive
has been off for more than 3 to 5 seconds. When the engine first enters
RESET, the microprocessor initiates a system check to determine if the
system, transformer and engine are operating correctly. This takes
approximately 2.2 seconds during which you will hear the engine’s startup
sounds begin. In order for Proto-Sound® to properly initiate the system
check, do not advance the transformer throttle past 10 volts when you first

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MTH SD70MAC Operating Instructions
enter RESET, wait for the diesel startup sounds to begin and then slowly
turn the transformer throttle to the off position and then back on again to
enter the forward phase. Interrupting the power too quickly may cause the
system to re-enter RESET (signaled by two dings of the bell). Should this
happen, wait longer before interrupting the power to enter the Forward
phase.
Proto-Sound® comes with several programmable functions, including
remote Diesel Engine Volume Adjustment, Separate Bell Button Operation
(pre-programmed at the factory), Horn In Neutral Operation,
ProtoCoupler™ On/Off Control, Squeaking Brakes and Passenger Station
or Freight Yard Proto-Effects. Each of these features are described in more
detail later. You will notice that when in RESET, your engine will not
respond to the whistle button with a horn blast or continuous bell ringing.
In fact, when in RESET and the whistle button is depressed, only one single
bell chime will be heard each time the whistle button is pressed. If you
don’t want to configure or change your locomotive using any of these
programmable features, simply leave RESET and wait 2.2 seconds before
interrupting the power to put the engine in forward. After you leave
RESET, your engine will operate normally in all the direction states of
forward, neutral and reverse. Remember though, once power is turned off
for more than 3 seconds, the next time power is applied to the track, your
engine will be back in RESET.
HORN OPERATION
Your Proto-Sound® equipped engine features a digital recording of a
diesel horn. The horn sound can be activated anytime the engine is in
forward or reverse by pressing the horn/whistle button on your transformer.
The horn will continue to blow as long as the horn/whistle button is
depressed. The horn will not function in RESET and must be configured
through a RESET option to allow the horn to work when the engine is in
neutral. See page 21 for information on horn programming in the Using
RESET To Program Proto-Sound®section of this manual
BELL OPERATION
Your Proto-Sound® equipped engine also features a digital recording of an
actual steam engine bell. The bell can be turned on or off by simply
pressing the Bell button on your transformer anytime the engine is in
forward, neutral or reverse. The bell will continue to ring until the bell

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MTH SD70MAC Operating Instructions
button is depressed a second time. Note: The bell will not function in
RESET. .
In fact, because of Proto-Sound® state-of-the-art design, the
microprocessor remembers its last command. Therefore, unless you turn
the bell off before you quit running your train, the next time you run the
engine, the bell will come on. No matter whether you come back an hour
later or a year later, the bell will begin chiming once the engine enters one
of the three directional states.
To turn the bell on using the transformer’s whistle button, turn on power to
the track and cycle the engine into NEUTRAL. Turn the throttle to 8 volts
or less (any higher voltage will arm the ProtoCoupler™) and press the
whistle button. The bell should begin chiming. To turn the bell off, press
the whistle button again. If you want to keep the bell on while running the
engine, simply interrupt the power with the transformer throttle or the
transformer directional switch and enter forward or reverse.
PROTO-COUPLER™ OPERATION
Your SD70MAC ProtoSound®-equipped locomotive is equipped with two
coil-wound ProtoCouplers™ for remote uncoupling action. Because the
ProtoCoupler™ is controlled through Proto-Sound® microprocessor, it
doesn’t require an uncoupling track section or modification to your layout
to function. The three simple steps below are required to operate the
coupler.
1. Put your engine in NEUTRAL and turn the throttle all the way up.
2. Press the transformer whistle button to “Arm" the coupler. (You
will hear a “Clank").
3. After arming the coupler, press the whistle button again to open
the coupler.
When the knuckle fires open you will hear the buzzing of the coil
energizing and the sound of the air lines coming apart. It can best be
described as a CHA-CHUSHHH sound. The coupler doesn’t have to be
fired in NEUTRAL. Once the
coupler is armed it can be fired
in Forward, Neutral or Reverse.
However, you may find that the
coupler doesn’t open when H H
Put Engine In Neutral
At Full Power
Press & Release
The Whistle Button Press & Release
The Whistle Button
Listen For The
Ca-Clunk Sound
See The Coupler Open
And Listen For The
Cha-Chusshh Sound

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MTH SD70MAC Operating Instructions
firing the coupler at high speeds. Reduce the voltage setting on your
transformer if this occurs and run your engine at a slower speed before
firing the coupler. If the coupler continues to open erratically, try
lubricating the knuckle with
light oil as indicated in Fig. 3.
For multiple heading purposes,
only one of the two
ProtoCouplers™ will function at
any one time. Use the coupler
direction switch as shown in
Figure 4 on page 18 to select
either the front or rear coupler.
Simply slide the switch toward
the direction of the coupler you want to make active.
DIESEL CAB CHATTER SOUNDS
Whenever your diesel locomotive is parked in Neutral, randomly played
“Cab Chatter” sound effects will occur every 2 to 30 seconds. There are a
total of four of these Cab Chatter sequences that capture authentic radio
transmissions between dispatcher and engineer. They are designed to play
at random intervals to eliminate repetitive and boring sequences though
there is no guarantee that you won’t hear the same message repeated two or
more times.
SQUEAKING BRAKE SOUNDS
Proto-Sound® equipped engines feature the ability to play the sound of
squeaking brakes whenever your engine slows in speed. There are two
settings for activating the squeaking brake sounds. The default setting
allows the brake sounds to play while the engine is in forward or reverse
and the transformer throttle is lowered from a high setting to a low setting
(14 volts to 8 volts or less). The sound itself is a stored recording on the
Proto-Sound® software chip and will always play the same brake sound for
the same three second length
each time the voltage is reduced
from high to low. Some practice
may be required to synchronize
the playing of the brake sounds
with the movement of the
Lubricate
Proto-Coupler®
Knuckle
Figure 3: Lubricating The ProtoCouplers
Throttle Down From
High Voltage To Low Listen For The
Squeaking Brake Sounds

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MTH Centipede Operating Instructions
engine. It is not uncommon for the engine to stop before the brake sound is
completed. Operators will find that coordinating the movement of the
throttle setting from 8 volts to off will allow the engine to maintain its
movement while the brake sounds play. Note: The brake sounds will not
be heard if the transformer throttle is not set above 14 volts and/or not
reduced below 8 volts.
TIPS ON USING THE SQUEAKING BRAKE FEATURE
Users will find the squeaking brake feature to be a very
realistic way to simulate the sound of an engine slowing down
for curves, crossings or coming to a stop at a station, side track
or switch yard. However, you may find that your engine
continues to play the brake sounds once your engine comes to a
stop, or that the sounds stop before the engine comes to a
complete halt. For example, if you simply run the engine and
turn the throttle off quickly, the brake sounds will likely
continue playing even though the engine has come to a
complete stop.
This effect can be eliminated by simply practicing with the
brake feature. In no time, you will quickly learn how to
“feather" the throttle to keep the engine moving while the brake
sounds play and then turning the throttle off just as the sounds
stop.

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MTH SD70MAC Operating Instructions
Operating Proto-Sound Freight Yard
Sound Effects Freight Yard Sounds (FYS)
Proto-Sound® is equipped with operator controlled Freight Yard Sounds,
referred to as FYS. The FYS sequence is designed to simulate the arrival,
unloading, loading and departure of a freight train in a freight yard. This
easy-to-use feature allows you to play digitally recorded sounds of
freight yard operations while your engine is parked in the Neutral State.
No additional wires or modifications are needed to enjoy these amazing
sound effects. The sounds themselves are randomly “shuffled” by the
Proto-Sound® computer. This gives the system the ability to play the
various sounds in a different order each time FYS is enabled.
Quick Overview- FYS Sounds
The following is a quick over view on how you can operate FYS.
The train on track moving Forward or Reverse direction.
BPress and Hold Bell Button For 3+
Seconds, Listen For a Horn Blast or
Air Release, then Remove your Finger
fromtheButton.
BPress Bell Button Again Quickly to
Stop Bell Chime.
Your train is now ready for you to play the FYS.