Wangrow SM-104 Stationary Decoder Set
Not in production

General: The Wangrow SM-104 is a four-address decoder.  Each of the four outputs can be programmed to a pulse of programmable length or a constant output.  The pulsed outputs can be set to drive a dual coil switch machine, while the constant outputs can operate signal lights, a stall motor switch machine, or an accessory motor.

To operate a dual coil machine, the two ends of the coil are wired to the outputs, while the coil center tap (or coil common wire) is connected to a separate common terminal.  For signal lights, the switch coils are replaced by lamps or LED’s.  For stall motor switch machines, the motor is wired between the two outputs without using the common terminal.

An LED on the circuit card illuminates when DCC packets are received, and a separate LED illuminates for each phase of each output when active.  This lets you easily see what the decoder is doing and if it is responding to your DCC data.

There is a provision for powering the unit from the track DCC or from an auxiliary DC power supply.  A jumper must be in place for powering from DCC, while it must be removed to operate from an auxiliary DC supply.  Not that this is the only unit that requires DC as an auxiliary power source.

A nice feature of the SM-104 is that the components that actually carry the load current are in sockets.  If you destroy an output by overloading it, you can replace the switch transistor chip and be up and running again.

Connections: Track and output connections to the SM-104 are by screw clamp terminal strips except for the manual switch control inputs.  These inputs are simply pins mounted into the printed wiring board.  It is unclear how to connect to them other than soldering wires, which is inconvenient if you need to remove the unit for repair or reprogramming.  There may be a mating connector, but it is not mentioned in the manual.

Feedback: The SM-104 has no provision for feedback to the cab bus.  If you need switch position feed back, then you must wire the switch position data into an auxiliary cab bus input such as the NCE/Wangrow AIU-01.

Programming: The SM-104 must be programmed on the programming track before you install it.  It is relatively easy to set up.  You write a value to two CV’s to set the base decoder address.  You write a value to each of four CV’s to set the function of the four outputs.  Basically, program 6 CV values and you are ready to install and operate.  The PR1 could not read the SM-104, but could program it in the CV programmer mode.  The NCE Powerhouse could read and write CV values with no problem.

Manual: I found the manual poorly written and difficult to follow.  The drawing in the manual did not match my unit, and the lines indicating connection points ended between terminals.  I had to spend quite some time tracing wires on the printed wiring board to make sure that I was connecting things properly. Starting from E1, the terminal order on my unit was: +DC, Blank, -DC, Blank, DCC, DCC.

Performance: I was disappointed to find that one side of the number 3 output of my test sample did not operate at all.  The other outputs appeared to operate correctly.

The SM-104 was able to operate the Tortoise™ switch machine with no problem.  I measured 9.8 volts run and 8.6 volts stall using 10.6 volts external DC.  I measured 10.7 volts run and 10.5 volts stall when operating from DCC.  Performance was solid with good torque.

The SM-104 was not able to operate the Nick & Jack International switch machine on either DCC or external DC.  The Peco dual coil unit functioned fine with good force on both DCC and external DC.

The grain-of-wheat lamps performed fine on both DCC and external DC.  I measured 11.9 volts from DCC and 10.0 volts when using a 10.6 volt external source.  This is good since there was little variation from DCC to external power.

The SM-104 really scored on the accessory motor. I measured 10.7 volts at 430 ma.  It had no trouble with this load at all.

Recommendation: The SM-104 is a BEST CHOICE for driving auxiliary motors such as found in accessories or turntables. This is the only unit that was able to operate my accessory motor, and it was able to operate it with authority.  It is a next best choice for stall motor switch machines.  It operates well with these units without external components and provides the convenience of four outputs in one location.  It is, however, more expensive per output than the Switch-It and must be moved to the programming track to change the decoder address.  If you are using dual coil switch machines such as the Peco, the SM-104 will work well with them.