My first Athearn rehab diesel project seems on track (no puns) so far, then I came across the 5-wire rewriting scheme from Roger(?) Furman. The images I am seeing come from more-modern versions of Athearn BBs. So: I get the part about throwing away the top contact strip and running wires from the motor top brass retainer strip to each wheel tower top inverted L contact piece. Why is there a need to switch the top and bottom motor retainer strips? The model I have has integrated one piece metal wheel covers, not the type that can be pried off leaving another smooth metal face. Given that, can’t I run the other wires from the motor (wires 3&4) to the lower metal contact on each wheel tower- the one that sits right on top of the gear assembly instead? Doesn’t that pick up rail current also? Those older wheel housings ( into which the axle ends go) seem to make it difficult to run wires soldered directly to them, without interfering with the wheel+tower movement when rolling. Any experts, please chime in, as this is my first in-depth Athearn effort. Thanks, Cedarwoodron
The reason for reversing the bronze motor brush contact strips is because the lower strip has tabs that stick out and touch the frame for electrical pickup to the lower motor brush. When installing a decoder, those tabs must not touch the frame. The upper motor brush contact strip does not have the tabs.
It’s also good practice to put a strip of electrical tape under the motor when it is re-installed.
The lower one has a prong that makes contact with the frame. Personally, I just bend the prong back up flush, but some folks like to swap the upper and lower to eliminate any possibility of breaking through the isolating tape that is used to isolate the motor from the frame.
Looks like two of us were answering at the same time. BTW it is not just good practice to isolate the motor with tape, it is essential. Just bending the prong or swapping the contacts won’t assure isolation of the motor. BTW, my preference is to use Kapton tape rather than regular electrical tape as I hate the sticky mess that regular tape can make.
From your description, it sounds like you’re NOT doing a DCC conversion. If that’s the case, and assuming you’re getting rid of the famous bonfire-in-the-cab lightbulb, I recommend removing said lightbulb and its supporting arm, snipping off the parts of the top strip that overhangs from the motor, and soldering wires between that top strip and the top metal tabs on each truck (pretty much what you’ve described). As far as ALSO running wires from the bottom tab to the “lower metal contact”, it is theoretically an equally good idea. But you’ve got to deal with space for the wires underneath the motor and also soldering the other ends of the wires to a much more difficult soldering area. But if you can pull it off, it sure seems better.
All the above is based on the original Blue Box Athearn drive system, as I remember it. It’s been awhile.
I’ll remind you that with the drive I’m describing (and the one I think you have), the frame is “live”, and if you couple it to another similar drive with metal couplers and that loco is “turned around” compared to the first one, you’ll get a short between the two.
Ed
Correct Ed, it is a dc rehab right now. I am ditching the front bulb assembly may keep the vertical metal tang as a support for a resistor- wired 3mm LED ( and am able to wire that item properly). I polished the original iron wheels and the protruding axle ends, free of any corrosion-they shine now. There seems to be enough space to run wires 3&4 to that lower metal contact on each wheel assembly- if I am generous with the wire length, then wheel assembly movement will not be an issue. If I’m not mistaken, the concept of the 5-wire rewiring is to do away with the frame as an electrical conductor, relying on the wheels (and their connection to the motor via those new wires) themselves. Is this correct? Also, I think liquid electrical tape painted generously in that space below the motor then regular electrical tape on top of that would be a longer lasting isolation technique than regular electrical tape alone, as the regular tape might dry out with the heat from the original motor over time. I am tapping a small screw into the side frame, for future dcc use, as per the Athearn rehab article instructions I am following. Further remarks invited. Cedarwoodron
While the photos show the more recent (compared to yours) version with inboard axle bearings, the wiring is similar. The loco shown originally had trucks with outboard bearings in after-market sideframes, and I added the plug-in feature to facilitate truck and gear maintenance. It consists of a small piece of copper-clad circuit board cemented to the loco’s frame. With the cladding split into two sections, shortened rail joiners were soldered to it, and short lengths of rail soldered to each of the wires leading from the trucks and to the motor. This allows easy removal of trucks or motor, although the latter is held in place with silicone sealant and is probably isolated from the frame. I’m running DC also, and don’t use operating lights. I body-mounted the couplers, so there’s no chance of shorting through the frames, as Ed described.
Wayne