Athearn loco + decoder

[Anonymous]

I have an Athearn GP 50 and I am currently installing a Digitrax DH123D decoder in it. I noticed that the motor has a contact against the bottom of the chassis itself. Is the chassis used as a conductor? Do I need to separate the two sides of the motor from everyone else?

[cacole]

YES, you must isolate the motor from the frame. To do this, you must remove the motor and cut off or bend up the small metal finger that sticks down from the center of the bronze strap that is on the bottom of the motor. This is easier to do if you remove that strap from the motor, but be careful that the motor brush doesn't fall out and get lost. Solder the black decoder wire to the frame and the gray decoder wire to this strap. Put a strip of electrical tape on the frame before you replace the motor, and insure that there is no electrical contact between the motor and frame. Remove the long, silver colored strap that runs from the front to rear truck, and throw it away. Replace it with flexible wire soldered to each truck, leaving enough slack for the trucks to rotate. Remove the top bronze strap from the motor, again being careful that the motor brush doesn't get lost, and solder the orange decoder wire to it and replace. The red decoder wire is soldered to one of the brackers on the trucks. The headlight bulb should be replaced with a 14 volt bulb that has wires connected to it instead of using the bracket that is in the locomotive. I glue the new bulbs in place with Goop, using the bracket that held the old bulb. You could probably leave the existing bulb in the locomotive, but there's no way to control it from the decoder if you do -- it will burn at full intensity all the time, and can't be turned off.

[dave9999]

QUOTE: Originally posted by cacole

YES, you must isolate the motor from the frame. To do this, you must remove the motor and cut off or bend up the small metal finger that sticks down from the center of the bronze strap that is on the bottom of the motor. This is easier to do if you remove that strap from the motor, but be careful that the motor brush doesn't fall out and get lost. Solder the black decoder wire to the frame and the gray decoder wire to this strap. Put a strip of electrical tape on the frame before you replace the motor, and insure that there is no electrical contact between the motor and frame. Remove the long, silver colored strap that runs from the front to rear truck, and throw it away. Replace it with flexible wire soldered to each truck, leaving enough slack for the trucks to rotate. Remove the top bronze strap from the motor, again being careful that the motor brush doesn't get lost, and solder the orange decoder wire to it and replace. The red decoder wire is soldered to one of the brackers on the trucks. The headlight bulb should be replaced with a 14 volt bulb that has wires connected to it instead of using the bracket that is in the locomotive. I glue the new bulbs in place with Goop, using the bracket that held the old bulb. You could probably leave the existing bulb in the locomotive, but there's no way to control it from the decoder if you do -- it will burn at full intensity all the time, and can't be turned off.

Or,buy the Digitrax DHAT no solder easy connector for Athearn.
http://www.digitrax.com/decinstall_files/image003.jpg Dave

[Anonymous]

Since blue is a common wire, can I solder it to the headlight bracket and the yellow or white wire to the other side of the bulb on the thin copper strip? And does it matter whether I solder the black wire to the frame or to the headlight bracket where it is more accessible?

[cacole]

According to the schematic diagram on the Digitrax Web site for their DHAT decoder wiring harness made specifically for older Athearn locomotives, the black wire can be connected to the headlight bracket, and the white wire is connected to the bulb's center contact. The blue wire is apparently not used in this configuration. The headlight bracket is fastened to the left rail pickup, which is the same as the frame. It's hard to tell from their drawing, but it appears that they provide a replacement for the spring contact that touches the back of the bulb, and is connected to the right rail pickup; otherwise, you're not going to have any control over the headlight.

[dave9999]

QUOTE: Originally posted by cacole

No, because the headlight bracket is fastened to the same electrical pickup that you're going to use for the decoder's input, and you will be creating a short circuit within the decoder. You can't solder the black wire to the headlight bracket because that bracket is the electrical pickup for the right rail, and the black wire needs to get power from the left rail. You may need to drill and tap a small hole in the frame and insert a screw to fasten the black wire, since soldering anywhere to the frame would be difficult. The suggestion to use a different (DHAT) plug-and-play decoder is still going to require removal of the motor so it can be insulated from the frame. It's been a while since I have installed a decoder in an older Athearn, but that DHAT probably also requires replacement of the headlight bulb. The newer Athearn Genesis locomotives have a totally isolated motor and don't require as much disassembly.

The DHAT comes with new motor mounts to isolate the motor from the frame.
This is more reliable than using electrical tape. Remember, one good short and
your decoder is toast. Dave

[cacole]

Dave,

That's true, but why spend an additional $8.95 for the DHAT wiring harness when you can achieve the same results by wiring the decoder directly to the necessary places? My impression from Train-Master's original post is that he is already in the midst of installing a decoder, and just isn't sure about some of the connections. For someone who doesn't know how to solder, or doesn't own a soldering iron, the DHAT might be worth the expense, but I haven't found it to be that difficult to solder six wires from a decoder to the required locations. The most difficult part of it all was removing and replacing the motor, which must still be done even with the DHAT. From looking at the Digitrax DHAT instructions, available on their Web site, I learned a simpler way to wire a decoder into an Athearn loco, though, and will keep their instructions in mind the next time I tackle one of them. I'm not so sure that the replacement bottom motor contact provided by Digitrax would still not require electrical tape between it and the frame to insure total isolation. Some Athearn motor mounts I have worked with allow the motor to move slightly from side to side or end to end when torque is applied, and that movement might be enough to allow that bracket to contact the frame. As you said, the least little bit of contact can turn a decoder into a smoke generator. I always use Kapton tape under the motor when adding a decoder. Kapton is so thin you can see through it, yet it is stronger and provides more electrical isolation than black electrical tape.

The newer Athearn Genesis are no easier, even though they proclaim to be "DCC Ready." First of all, you need a special decoder equivalent to the North Coast Engineering DASR, which also fits into Atlas and Kato engines and is a direct replacement for the constant lighting board in these models. The biggest problem with the Genesis locomotives are their headlight, rear light, and ditch light bulbs, which are 1.5 Volt bulbs and require the addition of resistors to operate on DCC.