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Athearn Genesis 2.0 HO scale EMD SD90MAC-H

Read this review from the September 2020 issue of Model Railroader
Athearn Genesis 2.0 HO scale EMD SD90MAC-H

Although the SD90MAC has been produced in HO before, previous releases modeled the early 4,300 hp version. This new model from Athearn Trains marks the first time HO scale modelers can get an accurate model of the later 6,000 hp version, the SD90MAC-H Phase II.

Part of the new Athearn Genesis 2.0 series, this high-horsepower heavy hauler is decked out with prototype-specific details. It’s also available factory-equipped with a SoundTraxx Tsunami2 dual-mode decoder and twin cube-style speaker sound system that operates on both Digital Command Control (DCC) and direct-current (DC) layouts.

The prototype. The six-axle SD90MAC was developed by General Motors’ Electro-Motive Division during the 1990s. In the locomotive’s designation, the “M” stood for its wide-nose, North American-style “comfort cab” and “AC” stood for alternating-current traction motors. The SD90MAC was designed around the 16-cylinder, 6,000 hp 265H diesel engine. However, technical problems with the brand-new engine led to most SD90MACs being delivered with a 4,300 hp 16-710 G3B engine.

More than 400 SD90MACs were built with the 4,300 hp engine, and none of the buyers took advantage of an upgrade program to retrofit the locomotives with the 6,000 hp engine when it became available. After 1996, all new SD90MACs included the 265H engine. These locomotives were designated SD90MAC-H. Railfans refer to later versions with a newly designed, high visibility cab as SD90MAC-H Phase II units.

Fewer than 70 SD90MAC-H locomotives were built. By 2010, original Class 1 owners Canadian Pacific and Union Pacific had retired their SD90MAC-H fleets. Some units found secondary service with the EMD Lease fleet and the Fortescue Metals Group in Australia.

The model. The Athearn model’s basic dimensions match builder’s drawings of an SD90MAC in the Car and Locomotive Cyclopedia of American Practice (Simmons-Boardman, 1997).

The model is accurately detailed as an SD90MAC-H, including a beveled long hood above the engine compartment. It also has the unique nose contours of the phase II cab. Molded details, including grills and panel lines, are well-defined and match prototype photos. The cab door also doesn’t have a window, correct for its UP prototype.

Other roadname-specific details include the antenna dome on the cab roof and long sunshades. The handrails and stanchions are made of flexible plastic to resist breaking. All grab irons, rubber m.u. hoses, see-through etched-metal steps, and other detail parts are separately applied.

On our DCC-sound-equipped sample, the Tsunami2 decoder is mounted above the motor. Twin cube-style speakers are in the enclosure above the rear truck.
Back end of an Athearn Genesis 2.0 HO scale EMD SD90MAC-H showing see-through screens and steps
The model features LED lighting and separate detail parts, including see-through screens and steps.

The mechanism. After removing the coupler boxes and two additional screws on the frame, I could lift off the plastic body shell. The flywheel-equipped motor is mounted in the center of the die-cast metal frame. Drive shafts and worm gears transfer power from the motor to the truck-mounted gear boxes.

Instead of the lighting board with a DCC socket featured on the DC version, our DCC-sound-equipped review sample featured a SoundTraxx Tsunami2 decoder mounted above the motor. Plastic clips connect the lighting, power pickup, motor, and speaker leads to the decoder board. The cube-style speakers are housed in a rectangular enclosure above the rear truck. This decoder doesn’t include a CurrentKeeper stay-alive circuit.

Performance. As shown in the charts above, the model accelerated smoothly from 4 scale mph to a prototypical top speed of 80 scale mph. Force meter tests showed the SD90MAC produced 3.7 ounces of drawbar pull, which is equivalent to 52 free-rolling HO freight cars on straight and level track. This pulling power was also confirmed during a hill climb test on our Milwaukee, Racine & Troy layout where the SD90MAC pulled 15 freight cars up a winding 1.5 percent grade followed by a 3 percent grade without slipping or stalling.

Even with its long wheelbase the model easily negotiated the no. 5 and no. 6 turnouts of various yard tracks. All wheels pick up track power, so the lights and sounds remained steady.

A free user manual is available for download at SoundTraxx.com. All the sound, lighting, and performance features of the decoder can be programmed using configuration variables (CVs).

I set the decoder address to the locomotive number, added acceleration and deceleration momentum, and enabled the three programmable braking rates.

To simulate the locomotive running light, I set the independent brake for a quicker response. To simulate air brakes stopping an entire train, I set the train brake for a longer response. I also set the dynamic brake to slow the train when that feature was enabled by pressing function 4.

Other user-triggered features include the bell, long and short horn blasts, and coupler sounds. Ground lights come on when the locomotive is powered up, but separate buttons control the ditch lights and directional headlights.

Function buttons can be used to manually notch the engine sounds up or down, but I enjoyed the realism of the Tsunami2’s Dynamic Digital Exhaust feature, which I calibrated according the instruction manual. The sounds of the EMD 265 then became even more prototypical as the engine notched up or down automatically according to the load placed on the locomotive or whether it traveled up- or downgrade.

Motor performance can be further fine-tuned with a custom speed table or one of 16 preset speed curves. There’s a special preset speed curve designed to optimize the SD90MAC’s performance when consisted with first-generation Tsunami-equipped Genesis locomotives. The Tsunami2 supports advance consisting and includes CVs 21 and 22 so that function control can be set to operate under the advance consist address.

DC operation. Like most dual-mode models, the SD90MAC-H requires a lot of power to get rolling. On our DC test track, the model’s lights and sounds came on after I applied 7V to the rails. After I advanced the throttle to 9.5V, the locomotive rolled smoothly at 1 scale mph. At our power pack’s 14V maximum, the engine reached 50 scale mph, below that of the prototype, but fast enough for most HO railroads.

The only sound effects in DC were the engine RPM. Under 10V, sounds cut out momentarily when I flipped the direction switch. Automatic sound effects for DC operation can be added, but this requires a DCC system or a Model Rectifier Corp. Tech 6 sound controller.

An impressive locomotive. Modern-era HO scale modelers looking to add a distinctive brute to their rosters will definitely want to check out the Athearn Genesis 2.0 SD90MAC-H.

Facts & features
Price: $339.98 (DCC sound), $249.98 (DC no sound)
Manufacturer
Athearn Trains
1600 Forbes Way, Suite 120
Long Beach, CA 90810
athearn.com
Era: 1999 to present (to 2006 as detailed for UP 8522)
Road names (multiple road numbers, except as noted): Union Pacific, Canadian Pacific, EMDX (no. 90 only, demonstrator scheme), and Fortescue Metals Group
Features
• All-wheel drive and electrical pickup
• 21-pin DCC socket (DC version)
• Die-cast metal frame
• Five-pole skew-wound motor with dual brass flywheels
• Light-emitting diode (LED) headlights, ditch lights, and ground lights
• McHenry plastic scale knuckle couplers mounted at correct height
• Minimum radius: 22" or greater recommended
• RP-25 contour metal wheels in gauge
• SoundTraxx Tsunami2 dual-mode decoder (DCC version)
• Weight: 1 pound, 7.5 ounces

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