Problem Installing a Sound Unit in Boxcar

Discussion in 'HO Scale Model Trains' started by petey, Aug 18, 2006.

  1. petey

    petey Member

    Hello Folks,
    Have a problem. I have installed a simple sound unit in this car, using Mantua tender trucks. The screw running up through the bolster provides a connection point for the needed track power.
    These are the simple connections: a wire to each truck; two wires to speaker; 9 volt battery plug. As you know, Mantua's trucks have two brass wheels on one side; two plastic on other. These wheels of course, are on opposite sides of the car when mounted.
    When I placed the car on the track and applied power, nothing.
    Then I accidentally derailed the trucks, so that only one brass wheel on each truck was touching their respective track. Got sound!
    My question is, now what orientation of the wheels is the correct one. Obviously, the standard Mantua arrangement does not work.
    Do I rotate an axle on each truck, so that each truck has a brass wheel on each rail? If so, is there a particluar orientation for the 'opposite' brass wheels, i.e. should the two end axles have brass on the 'inner' track (track farthest from viewer). It seems to me that orientation shouldn't what's going on?
  2. Russ Bellinis

    Russ Bellinis Active Member

    You need to put one truck on the car in the same polarity as a stock Mantua tender. The other should be reversed. You need one set of brass wheels on one track; the other set on the other track.
  3. pgandw

    pgandw Active Member

    Does the car have a metal underframe? If so, at least one truck has to be insulated from the frame or weight or any other metallic link between the two truck mountings.

    On a Mantua tender, all brass tender wheels pick up from the same rail, and the locomotive picks up from the other. The tender has an insulated drawbar connection to the locomotive, and a wire directly from the non-grounded motor brush to the tender frame. The tender trucks are not normally insulated from the tender frame.

    Since all the pickup is contained within the 2 trucks, 1 truck must pick up from one rail, and the other truck from the other rail. Both brass wheels on one truck are set for one rail, and both brass wheels on the other are set to the other. There must no electrical bridge across the trucks except the sound unit. The speaker and battery should connect to the sound unit, but be totally insulated from any metal frame and/or the trucks.

    Hope this makes sense and helps
  4. petey

    petey Member

    I am not setting up a tender--and not connecting to a locomotive---so the circuit must be completed using only the tender trucks. The sound unit is installed in an all plastic box car. Anticipating the circuitry, I had, as Russ indicated, put the brass wheels on opposite rails. Rather surprised that it didn't operate. Then, in spite of suspecting it would not work, I put both brass wheels on one side. 0 sound.
    Began some power pack lead touching; when leads are connected to the tender mounting screws, good SOUND; when leads are touched to the truck frames; good SOUND; when leads are placed on truck axles, not as consistent SOUND(this may signify nothing); when car is off track and a lead is placed on each set of brass wheels, good SOUND. Orientation of wheels, when off track makes no difference.
    Is it possible that the sound board is creating an 'in-out-path' electronically, so that orientation of circuit carrying wheels is not necessary, and, if fact, this orientation defeats the board circuitry? Would the change to pickup wheels on ALL axles cause this to emit sound?
  5. doctorwayne

    doctorwayne Active Member

    These two statements are seemingly contradictory: the brass wheels pick up power from the rails, transmit it through the axles, to the truck sideframe, and then to the bolster screw. I would check to ensure that the brass wheels haven't, at some time, been secured to the axles with CA: even a thin coating will not be conductive. While you have the wheelsets out of the sideframes, check the bearing holes for any build-up of crud, which might cause intermittent electrical contact with the axle ends. If you really think about it, the electrical path that I've described is pretty tenuous at best, even though this system was an industry-wide standard for steam locomotives at one time. Perhaps wheel or axle wipers, or track pick-up shoes, wired directly to your sound unit would prove more reliable.

  6. Russ Bellinis

    Russ Bellinis Active Member

    I think Dr Wayne is right. It sounds more like a bad electrical connection between the wheels and side frames of the truck, than an electrical problem with the way it is wired.
  7. petey

    petey Member

    It is a bad/intermittent electrical connection. It appears to be the connection between the positive battery wire and the sound board. I played with it and it seemed to work more consistently when I pushed the red wire toward the board. It's now been chuffing for 10 minutes, all though, on occassion with movement, the wire makes a micro movement, so that it doesn't work. At this point, I believe that with movement on the layout, it is appears more likely to keep working.------WRONG-------- when on the move, while it keeps on sounding, the movement causes a connect/disconnect, resulting in a syncopated chuff, rather than the even chuff of a loco running at a constant speed.
    This is frustrating; after buying a new car, new appropriate trucks, new sound unit, to be confronted with a mystifying problem having nothing to do with wiring, truck conductivty, or the new car. Now I must consider diagnosing the sound unit and probably having to repair my 'new' electronic sounder.
    Thanks for the responses, fellas.
  8. Russ Bellinis

    Russ Bellinis Active Member

    Ddid you buy the sound unit locally? It should be replaced under warranty.
  9. petey

    petey Member

    Boxcar Sound nit

    Hello Russ,
    This is a CMI unit. They marketed these in diesel and steam sounds. The diesel isn't much to listen too, but the steam provides a pleasant chuff, particlularly for the money.
    Just to find out, I searched for CMI on the web. They came up; they do other things besides modeling, which I believe was a minor sideline. They produced two different power packs, called, 'Sounders', and---these sound units. Sent an email to the model railroad division. Email returned as a failure.
    This is the kind of thing that puts a moderately involved modeler out of the hobby.
    You know of a good electronics guy?
  10. Russ Bellinis

    Russ Bellinis Active Member

    Do you have a local hobby shop. Often, you will have folks working at a hobby shop who can solder bad connections for you.

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