Quantum Magnum Decoder in LGB Mogul Steam Installation
by Paul Turvill
Paul Turvill from Whidbey Island, Washington, documents in detail a Quantum Magnum steam sound decoder installation an LGB Mogul.
Introduction
The release of the Quantum Magnum version of the Aristo G scale decoder by QSI Solutions has facilitated the addition of sound and DCC control to a wide variety of G and other large scale model locomotives. The Magnum is a robust, high-capacity decoder, capable of driving DC motors requiring up to 2.5 amperes of continuous current. It also provides a full range of sound options, and its firmware “personality” is user-upgradeable using the Quantum Programmer and Q2Upgrade software, also from QSI Solutions.
The Magnum decoder is physically identical to the Aristo version, but includes an adapter board with screw terminals to facilitate installation in virtually any large scale locomotive. The adapter board is socketed to emulate the standard Aristo connections, and the ways in which it may be installed in your locomotive is limited only by imagination. This document details the installation of a Magnum decoder in an older “limited edition” LGB Mogul locomotive, which was a part of the Circus Train Subscription made available by Depot G Hobbies during the 1980’s.
Planning the Installation
Since the LGB locomotive itself is mostly filled with cast lead weights, I decided early on to do this project as a tender installation. The included tender had only a single weight located above the aft truck, probably to prevent derailments when pulling a heavy train through those tight minimum radius LGB curves. Otherwise, the tender interior was reasonably clear of obstructions. The tender also included a backup light and electrical pickup for both itself and the loco, and a six-pin socket which mated with a cable intended to convey current to a matching cable at the rear of the loco. Only four of the six pins were used (power pickup from the tender, and the switched backup light) in the original model, but the other two proved to be a bonus, since my decoder installation requires all six: two for power from the loco’s track pickups, two to send the decoder’s motor output back to the loco, and two more for the headlight. The original backup light connection would not be required, since that will be handled all within the tender.
Perhaps the most difficult part of the planning process was analyzing the existing wiring to the motor and headlight, and coming up with a suitable routing to the plug that would eventually mate with the tender. Fortunately, the LGB Mogul was mostly made up of molded plastic components, and the motor brushes were easy to isolate from the original electrical pickup system by simply rearranging a couple of plug-in connections. The original 16-volt incandescent headlight lamp was rather dim, so I decided to convert it (and the tender’s backup light, as well) to a 5 millimeter Yeloglow LED from Miniatronics. This would require re-routing the original headlight leads, disconnecting them from the loco’s built-in circuit board and connecting them to the tender by way of the six-pin plug and socket connection. It would also require a series dropping resistor, which I decided would be easier to install in the tender.
Finally, the wires that originally connected the electrical pickups directly to the motor would have to be unplugged from the original motor terminals and re-routed to the new six-conductor cable, and a new pair of leads installed from the six-wire cable to the motor terminals.
At the tender end, it would be simply a matter of mounting the decoder, speaker, and other components, and making the required connections to the screw terminals on the Magnum adapter board: two DCC input leads from the tender and loco pickup pins of the six-pin socket; two motor power leads to the socket; a pair of leads and a series resistor to the pins for the headlight; and a pair of leads with a series resistor to the backup light.
Some folks who are more adventuresome than I may want to consider adding two more leads and finding a place to mount a speaker in the locomotive rather than the tender, to put the sound closer to the “source.” But simplicity won out in my case, and, as it turned out, tender-mounting the speaker has some definite advantages: lots of room, and the volume of the enclosed tender provides a very competent enclosure which greatly enhances the quality and volume of sound from the 2” diameter speaker.
Wiring the Locomotive
Most “generic” installations of the Quantum Magnum decoder will probably not be in this make and model, so this discussion will spare many of the gory details and focus on the general principals of rearranging the original wiring and providing the necessary new wiring for the motor and headlight.
Removing the boiler and cab reveals the internal wiring. Inner leads at chassis are the rail pickups; outer ones connect to motor brushes. Headlight leads (top) have been rerouted to the new six-wire cable. Smoke generator wiring was not changed.
After removing the boiler housing and cab from the chassis, I unsoldered the original four-wire cable from the loco’s circuit board and disassembled the IDC plug from the other end, being careful not do damage it. I installed the original plug on one end of a length of six-conductor flat ribbon cable, and after slightly enlarging the entry hole at the back of the cab, pushed the other end into the area under the loco’s circuit board. Two of the cable’s leads were connect to each of the following (see photo): the loco’s track pickup pins, the headlight leads (unplugged from their original location on the circuit board), and the motor brush leads. To avoid removing and replacing the original “plug-on” connectors, I simply cut the original wires and spliced them to the business end of the six-wire cable.This LGB model came equipped with a smoke generator and a three-position switch for controlling it and the lights (position “A” = fully off; “B” lights and smoke; “C” all on). The new wiring scheme for motor and lights bypassed the original circuit board, of course, but I left the smoke generator connected so that it is still controlled by the switch.
Replacing the headlight lamp was a bit of a challenge, but well worth the effort. The original incandescent lamp was a two-pin unit and simply plugged into a small socket. The LED I selected to replace it needed to be adapted by “sculpting” and trimming its leads so that it could be plugged into the socket, and at the same time be oriented with its “lens” end facing the business end of the molded plastic headlight housing. While I was at it, I applied the same technique to the backup light as well.
A 5mm LED was modified to replace the original 16v. incandescent lamp. Its leads were bent to approximate the position of the original, but with the “lens” end facing the front of the plastic headlight housing.
With the loco wiring completed and tested for correctness and continuity, I was ready to reinstall the boiler and cab to the chassis. The extra lead lengths were simply tucked into the space at the rear of the boiler above and below the circuit board.
Preparing the Tender
The major modifications to the tender were mounting the decoder itself (actually the “adapter board” that makes the Aristo decoder into a Magnum); locating and mounting the speaker; and adding the necessary wires to the six-pin connector.
Prepping the tender included locating the various components and creating a “speaker grille” with a 3/16” drill. The Magnum board was mounted on “posts” of ½” 2-56 machine screws.
After trial fitting everything in the tender, I got out the electric drill and went to work. I decided to mount the speaker facing down against the tender floor, and to use the relatively air-tight tender shell as its enclosure. This required creating a “speaker grille” by drilling an array of 3/16” diameter holes in a pattern that would be completely covered by the disk of the 2” speaker. Next, I drilled three #50 mounting holes in the Magnum adapter board, and using the drilled board as a template, duplicated the pattern in the tender floor.
I mounted the speaker over the “grille” with a couple of drops of CA adhesive, and created three mounting “posts” for the adapter board using ½” long 2-56 screws and nuts in the previously drilled holes in the floor. I then ran extra 2-56 hex nuts about 1/8” onto the “posts,” followed by the adapter board and three more nuts. This provides a solid mounting with clearance all around. See photos.
Next I removed the forward truck from the tender chassis to reveal the circuit board there. After unplugging all of the wires and removing the board from the chassis, I did enough drilling, cutting and “jumpering” of traces to achieve the connections I needed between the six-pin header and the “plug-on” pins of the board, where I made most of my connections to and from the adapter board. I installed a 470-ohm resistor on the bottom side of the board in one of the headlight traces. Both wheels on each tender axle have pickups, so it was a simple matter to connect the right- and left-rail tender connections in parallel with the corresponding leads from the locomotive.
Top: modified tender circuit board with jumpers added by the author. The 470-ohm resistor is in series with a headlight lead. Bottom: magnets mounted to tender truck axle are used to trigger magnetic reed “chuff switch.”
With the modified tender circuit board reinstalled, I proceeded to make the necessary connections between the pins on the circuit board and the screw terminals on the Magnum adapter board. I added a series resistor to the end of one of the backup light leads and insulated it with a length of heat-shrink tubing before connecting them to the board. All of the other connections were made exactly per the Quantum Magnum documentation.
The Quantum Magnum decoder permits the use of a magnetic reed switch for adjusting volume and resetting the decoder, and an optional “chuff cam” switch. Since this was a tender installation and the LGB has no cam, I decided on an alternative solution. I mounted a pair of small magnets diametrically opposed on one of the axles of the tender’s lead truck, and added a miniature reed switch. The arrangement causes the “chuff switch” to close twice per axle revolution; and since the tender wheels are just a little over half the diameter of the loco’s drivers, the result is close enough to four chuffs per revolution to please all but the most discriminating observers.
Finally, I used a piece of tape to secure the magnetic reed switch used for volume control and decoder reset functions inside an upper rear corner of the tender shell. Its use is optional, but it’s there if I should ever decide I need it.
Installing the Magnum Decoder
Since all of the pre-wiring was done in the above two sections, all that remains is plugging the decoder into the adapter board, plugging in the speaker, magnetic reed switch, and cam switch connector (if used).
Left: magnetic reed switch used for volume control and reset functions is taped to inside of tender shell. Right: the finished installation, with speaker, chuff switch and magnetic reed switch all plugged into their respective sockets.
It’s a good idea to test everything before fully reassembling. If everything is correctly connected, the engine runs at the default address of 03, the lights work, and some sort of sound comes out of the speaker, it’s time to do a little programming. The Quantum Magnum can, of course, be programmed by most DCC systems, but by far the best programming solution is to use a Quantum Programmer and Quantum CV Manager software. This combination provides a comprehensive graphical interface that encompasses all of the new features available in the Magnum decoder. Additionally, the Q2Upgrade software package provides the ability to upgrade the decoder’s firmware whenever a new or updated version is made available by QSI Solutions.
There’s no specific firmware for an LGB Mogul, so I selected a Magnum preprogrammed for the next best thing: the Aristo Mikado. I plugged in the “chuff cam” switch described above and spun the magnet-equipped axle to ensure that it was producing the expected two closures per revolution. Then, using the supplied “magic wand” magnet, I activated the reed switch from outside of the tender shell to confirm that it was functioning as expected.
Finally, I placed the tender shell on the chassis, put the loco and tender on my test track, dialed up address 03, and confirmed that everything was working. Even with all of its CVs set to their default values, performance was immediately impressive. And after tweaking some of the Quantum Magnum’s many, many available “performance” settings with Quantum CV Manager, the performance is as good as just about any DCC locomotive and decoder combination I’ve seen, and better than most.
Conclusion
My Quantum Magnum decoder-equipped Mogul is an impressive performer. With the help of my Quantum Programmer and Quantum CV Manager software, I was able to set up and calibrate a full range of features, including such niceties as the built-in Odometer function and BEMF-based speed calibration, as well as all of the other features common to the QSI line of sound decoders.
Sound quality is impressive, and the output volume is more than adequate for just about any indoor or outdoor situation. On my test track, I had to reduce the master volume (CV51.0) to a mere 32 (in a range of 0-255), to avoid hurting my ears. The unit performs well throughout its speed range from well under 1 smph to about 45 smph, and after some tweaking, the verbal speed readout gives results that are within a few percentage points of my calculated values throughout the range. Errors in the verbal odometer readings (a feature of Quantum CV Manager) are virtually nil.
LGB’s “Circus Train” 2-6-0 Mogul equipped with the Quantum Magnum decoder from QSI Solutions ready for testing on the author’s dual gauge test track .
