Trying to upgrade an engine to DCC

Model Railroader Layouts and layout building
1

I have been having no luck in converting an early model proto 2000 GP20 to DCC. The engine originally had a printed circuit board that controlled the power and directional lighing. I am trying to use a digitrax DH163D decoder to
be able to run the engine on my newly rewired DCC layout. I am having little luck. When I put the engine on the program tack and try to program it, I get nothing, only when I move the front truck left wheels to the right rail, then I can program the decoder. I haved asked digitrax about this and they told me I incorrectly wired the decoder. I wired the decoder red and black power wires to the wheels to the same points that the original wires where on. I even tried reversing the wires with no luck. It seems that both the connections coming from the trucks are on the left rail side and that the original PCB controlled the power. Is there anyone out there that has successfully wired an engine like this to run under DCC or can anyone give me some advise on what I am doing wrong.

2

It almost sounds to me as though the motor in the loco is not isolated and you’ve set up some sort of short or ground loop in the decoder. I don’t know what the GP 20 looks like inside but try popping the motor off of the frame and see what happens. If it needs to be isolated (suprised you didin’t fry the decoder if this is the case), a simple piece of electrical tape usually does the job (like on older athearn locos)… Digitrax is correct, something isn’t wired right…

Good luck,
Jeff

3

When you’re isolating the motor, you must make sure that no part of the motor remains in contact with the frame. Electrical tape usually does the job, but remember to replace the metal screw with a nylon screw. (These are 2-56 screws, almost universally.) If this is a frame-ground motor, then you may have only 2 wires, 1 from each truck, on the same side. These should go to the same point on the decoder (red or black wire). Then, you need to make a connection from the frame to the other decoder “rail power in” lead.

To start, don’t connect any of the lights. They may also be frame-ground, so that could cause problems.

Can you post a picture?

4

The frame should be the left-hand rail connection, and the wires from the trucks are the right hand rail only, if memory serves me correctly, because early Proto engines were exact copies of Athearn drives.

If you have a VOM with a continuity check function, disconnect the wires from the decoder. Touch one probe to the right rail and then to each wire from the trucks. If they both sound off, then both trucks are connected to the right hand rail and the frame itself is going to be the other rail’s pickup point. If you get no sound from either truck, then try the left hand rail. Either way, I think the wires from both trucks are connected to the same side. If this isn’t the case, then go to the next paragraph.

The lower motor brush may be connected directly to the frame for electrical pickup. The only way to know for sure is with a VOM. Touch one probe to the lower motor brush contact, which should be a bronze strip that can be seen at either end of the motor. Touch one probe to it and one to the frame. If you get a tone, the motor is in direct contact with the frame, and must be insulated. This will require removal of the motor and modification of the bronze contact to eliminate the prongs that touch the frame, and then insulating the motor from the frame with electrical tape as it is put back in place.

5

Thanks for the great response. I think the motor is isolated because it is held to the fram by two rubber mounts that go into the bottom of the frame and the bottom of the engine where the lower contact strip is attached to the engine has a resin cover on it. I will try your suggestion to see if I can get it working Thanks

6

Thanks for the great response. I think the motor is isolated because it is held to the frame by two rubber mounts that go into the bottom of the frame and the bottom of the engine where the lower contact strip is attached to the engine has a resin cover on it. I will try your suggestion to see if I can get it working Thanks
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7

Thanks for the great response. I think the motor is isolated because it is held to the frame by two rubber mounts that go into the bottom of the frame and the bottom of the engine where the lower contact strip is attached to the engine has a resin cover on it. I will try your suggestion to see if I can get it working Thanks

8

Ok, I didn’t see an answer to your question, or a response that you got it figured out.
SO…
I am looking at a Proto 2000 GP 20. You are dealing with a hot frame.

  1. I presume you have already removed the original circuit board and discarded it?
    If not do so. Once you do this the motor is isolated.

  2. Under the circuit board in between the two sides of the frame is a brass bar. That brass bar is the other motor brush contact. Solder the negative motor output from the decoder (grey) to this bar. Make certain the newly soldered lead cannot touch the frame.

  3. Solder the positive motor output (orange) to the red wire coming from the bottom of the motor (you have probably already done this).

  4. As another poster mentioned the two black wires from the trucks should be connected together and to the black power-in lead of the decoder. This is the left rail power.

  5. The power from the right rail is in the frame. Solder a small brass eye to the end of the red decoder power-in lead. Or I guess you could make an eye by soldering a loop into the wire. Connect it to the frame using one of the screws that was originally used to hold the circuit board.

Unfortunately I do not know for certain which lead of the motor is p