KB882: Installation of Digitrax Wired Decoders in Bachman Plus HO ABA F7s

This article was last updated on Oct. 28, 2010, 6:37 p.m. | Print Article | Leave Feedback

This note addresses the installation of an H0-Scale wired decoder into Bachmann Plus ABA F-7s; it calls for using a DH140, which has been retired.  Current decoders such as the DH123 or DH163 or similar wired decoders can be used.

Just finished up doing a few HO Bachmann Plus F7's, ABA's to be exact. Thought maybe some of you might be interested in how the DCC conversion went on these.

They are an easy conversion!

1.  The full stall current for these ranged from 500-700 ma for each loco . I selected Digitrax DH140 for the A units and a DH120 for the B unit, the B has no need for any other functions. Both the DH140 and DH120 are rated at 1.5 amps and are small enough to fit on the shelf in the rear of the frames. So you have a solid frame to heat sink the decoder and there is no plastic in the rear doors windows so there is good air flow across the decoder. But I really doubt it is needed.

2.  To remove the shell remove the 2 phillips head screws located in the holes on the bottom of the frame just behind the trucks, these are staggered off center of the frame, one left and right of center. Once the shell is off, unsolder the pickup wires and the lamp wire of the top motor brush tab.

3.  Now on the bottom again are two screws in the center of the fuel tank. Remove these and the fuel tank, these screws also hold the motor in place. You can now lift the motor out of the frame. Once the motor is out, you can remove the motor cradle off the motor. And you will see the long tab from the lower brush. Clip this long tab off close to the lower brush leaving just enough to fold over the brush holder and solder a wire on to bring up around the motor.

4.  But a drop of Areo-Car motor bearing lube on each end of the motor bearing, and a drop of Conduct-a-Lube on the commutator, now slip the motor cradle back on. The arrow on the motor points up.. Put the motor back in the frame with the brush end towards the rear of the loco. Put the fuel tank back on and put the two screws back in. Check the motor with an Ohm Meter and make sure the brushes are isolated from the frame. Once you are sure the motor is isolated all you have to do is wire in the decoder. But test the decoder first.

5.  The wire coming from each of the trucks are the right rail pickup and the frame is the left rail pickup. Solder the two wires from the trucks to the Red wire of the decoder. Just behind the head light you will see a solder lug screwed into the frame. One of the head light wires is soldered here, leave the lug screwed down and just unsolder the head light wire. Now solder the Black wire from the decoder here. Solder the Orange wire to the top motor brush tab, and the Gray wire to the wire you soldered to the bottom brush tab. I used the stock head light, so all you need to do is solder the White wire to one headlight wire and the Blue wire to the other headlight wire. You are now ready to put in on the program track or the PR1, if you can read the factory defaults, everything should be ok and you can program it up and put it on the layout. If not find out what is wrong before you put it on the layout.

6.  The headlight does a decent job of lighting the number boards, but if you are like me you may want to light these separate. Especially if you use on of the FX's on the headlight. The Mars light works fine with the stock headlight. I set mine to an off voltage of 10 and a rate of 2. It looks great to me.  But this would look strange if you did not light the number boards separately, as they will flash like a Mars light, too.

7.  To light the number boards is not really very hard. I just pushed the headlight lamp as far forward as I could, it already has a tube around it, slide the tube up also. This will keep the light from reaching the number boards. Also I painted the tube around the light flat black on the outside and made sure it stuck out a little from the end of the light.. The idea is to make sure the tube is up against the plastic for the headlight. I used 2 1.5 volt 15ma GOR lamps, wired in parallel. When you look at the front of the frame, you will see the shelf that the headlight sits on, you will also notice the corners of the front below the shelf are beveled on each side, this is for clearance for the number boards. I glued one light horizontal on each of the bevels just below the headlight shelf. I then took a 2 small pieces of black styrene and made a small hood over each of the lights, by gluing them flat on the headlight shelf over top of each light and let them stick out just a little more then the width of the lamp. Now they will not light up the headlight.. To wire up the number board lights you have a few choices. Using a dropping resistor you can wire them right across the track via the frame and the wires from the trucks. This way as long as there is power on the rails they will be light. Or you can wire one side of them to the Blue wire on the decoder and the side to one of the function wires. I used the Green wire, function 1 via a 510 ohm resistor. You could also use a 1.5 volt voltage regulator. This way I can turn the number boards on and off as I wish.  The value of the resistor will very depending on what lamps you use, how you wire them serial/parallel, ect. And also what voltage you use on your rails.

7.  KaDee also makes a coupler conversion kit for these, #452. These are a lot more work then putting in a decoder, but the 3ft spacing looks nice.

I know this looks like an awful lot, but in all honesty, it takes longer to write it, then do it.

This page is courtesy of Don Crano and is Copyright, 1997.

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