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.