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Thread: Replacing motor in my N scale Athearn Challenger (2017 release)

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    Default Replacing motor in my N scale Athearn Challenger (2017 release)

    In late August, my Athearn Challenger (purchased new in Oct 2017) started acting up AGAIN...

    This is a loco that spent 8 of its first 12 months back at Athearn for warranty repair, eventually traveling all the way to the factory in China for refurb, and back: (1) nearly all the axles were so far out of gauge (narrow) that they would not traverse ANY turnouts (these days, I would re-gauge them myself... but I was only 6 months back into N gauge, and had never encountered a loco so complicated); (2) the sound channel of the decoder died; (3) the front drive train froze (maybe), and was replaced (requiring the trip to China). I decided to attempt the diagnosis and repair myself, rather than wait 6 months for Athearn.

    Symptoms this time were similar to the last time (that got it sent back to China)... after running OK for anywhere from 1-20 minutes, the loco would start to draw excessive current and slow down. If it was in my reverse loop it would set my AR-1 autoreverse to chattering and the loco would halt. Surprisingly, it did NOT sound like the motor was laboring due to a mechanical bind... nonetheless, my first thought was a problem with either of the gear trains.

    After a couple weeks of teeth gnashing and hair pulling, I finally decided that there was NOT a mechanical bind anywhere in the loco... the clues being that I couldn't find/hear evidence of a bind, and the current draw reported by my NCE Powercab was as much as TWICE the stall current of the motor. I finally concluded it must be an electrical issue, either in the motor or the decoder. I disconnected the decoder and hooked its output to an old surplus motor I found, and it seemed to act normally... I then (with some trepidation) pulled the motor, reconnected it to the decoder, and found it would show the same faults (sporadic periods of excess current draw) even when removed from any mechanical linkages.

    I considered replacing the motor with a coreless motor from the web (and still might some day), but in the interest of getting my Challenger back in operation sooner, opted to get a factory replacement from Athearn. The new replacement motor arrived today, and I installed it this afternoon. When I first made the decision to attempt the repair myself, I did multiple web searches and was not able to find much in the way of useful info re: disassembling an Athearn Challenger or replacing the motor, so had to figure much of the following myself. I thought I would document it here, for anyone else that might need to do a similar repair... as it turns out, it's not really that difficult, because you DON'T have to disassemble the complete drive train (which is good, since I still haven't figured out how to drop the gear towers out of the loco!).

    STEP 1: The first step (the only one where useful info can be found on-line, but requires watching hours of Youtube video for 30 s of useful info) is removing the shell. There are two screws holding the shell: one in the forward stack, and a second under the small dome just in front of the cab. Stick a pin in the hole in the dome, and the dome can easily be wedged out, revealing the screw. Remove both screws, setting them someplace safe.

    01-Screw under dome.jpg

    Next, you need to "unlatch" the handrails from the back of the cab... the rails on either side of the cab are formed from a single piece of wire that extends under the back of the cab. using forceps or a toothpick, you slip the connecting wire out from under the back of the cab.

    02-unlatch handrails.jpg

    You should now be able to gently lift the shell off the mechanism... it might require a little rocking, but mine came off fairly easily... revealing the lighting and motor PCB (You can also see the handrails on the shell in this pic, green arrow)

    03-unsolder 8 wires.jpg

    STEP 2: Moving the PCB out of the way. To move the PCB board and access the motor, you will need to unsolder 8 wires from the PCB board (red arrows in previous pic); 4 from the front (2 power from the front axles and 2 LED); 2 from the middle (motor connections); and two more power connections coming from the rear drive axles. Label all the wires before you unsolder them! Most were black in my loco. I had already unsoldered these wires while diagnosing my problem. You do NOT need to unsolder the five wires from the decoder in the tender.

    The PCB is held by tabs on the front and rear plastic motor "yokes," pointed out by the probe (actually, my fly tying "bodkin") in these two images:

    04A-forward tabs.jpg

    04B-rear tabs.jpg

    If you gently wedge a jewelers screw driver under the PCB near these tabs, you can gently pry the board upward, and move it back out of the way, revealing the motor and drive train:

    05-fold back PC board.jpg

    Continued in next post...
    Last edited by NDave; 10th Dec 2019 at 01:06 AM.

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    STEP 3: Disconnect the fore and aft universal joints. The motor is connected to the fore and aft worm gears by 2 universal joints, with hex heads that fit into the front and rear flywheels and cup and sockets that engage the corresponding heads on the front and rear worms. These need to be disconnected before the motor can be removed. I found that you can use very fine forceps to reach in and slide piece connecting the worm to the flywheel TOWARDS the flywheel (in the direction of the arrow in each pic; it slides back into the recess in the flywheel).

    07A-disconnect universal joint.jpg

    07B-disconnect universal joint.jpg

    On my loco, there was an audible and tactile "CLICK" as the U-joint disengaged.

    STEP 4: Remove the motor... slip a screw driver into the small slot on each side near the front of the motor, and gently pry upward. I had to work from one side to the other, until the motor finally started to slide out. It's a tight friction fit. (NOTE: I forgot to disconnect the U-joints before I took this picture... but did disconnect them before I actually pried the motor out))

    08-Gently pry out motor.jpg

    Here are the OLD (top) and NEW (bottom) motors. The original factory motor was a five pole, the replacement is a 3 pole. Note the notch in the front right corner of the old motor (arrow)... this is for the wire to pass up alongside the motor (there's also channel for the wire in the front/ride side of the motor recess in the chassis). The new motor lacked the notched corner... don't know if it was necessary, but I used a razor to cut the corner (not shown).

    09-Old (top) vs new (bottom_.jpg

    The new motor came with leads already soldered to the solder tabs for the brushes.... BUT the red lead was too short. It will be down in the frame when the motor is installed, and the lead needed to be long enough to run up along the motor to be soldered to the PCB. I replaced the factory lead with a length of red wire that was long enough to reach...

    Continued in next post...
    Last edited by NDave; 10th Dec 2019 at 01:12 AM.

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    please accept that I am making sure I followed your post.

    you hooked-up or soldered in a different motor to the decoder and current draw went back to normal.

    this does seem a good conclusion. and Nice photos!

    If you have an volt-ohm-meter you should see a short across the motor leads or brush caps.
    ... I am assuming you have it out of the DCC circuit.
    the test is done to confirm the motor failure. it will give you confidence.

    on to my curiosity.
    the motors I have met mostly fail open and conduct no electricity.
    your motor is pretty consistent with one that has 'gapped' the commutator plates.

    once you are done the swap and satisfied,
    can we spend some time in another thread sharing how to inspect and if indicated
    clean and test the motor?
    I think you are looking at an event caused by the manufacturer...
    the problem is that they are going to give you the same 'fix' they did your last go 'round.
    to state my last guess more clearly, they do not know or care that the motor brushes are
    too soft for the service the motor is in.

    victor

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    STEP 4: Install the new motor. This step is just a little tricky. First, insert the hex heads of the front and rear U-joint pieces (as far as I could tell, these pieces are identical) into the corresponding recesses in the flywheel. I decided (with no evidence) that it would be best of the slots in each U-joint were aligned with each other, with the slots in the cups in a vertical orientation. Turn each of the worm gear joint ends so the tabs are oriented vertically, corresponding to the orientation of their sockets (no picture, but it will be obvious, when you look at it all).

    Set the motor into the recess in the frame, being careful not to turn the shaft (keeping the U-joints aligned). Route the wire coming from below (in mine, it was the red wire, which will connect to the "motor #1 tab) into the channel along the front right of the motor

    10-wire in channel alongside end of motor.jpg

    Sorry there are no pictures of this next operation... At this point, I nudged the motors rotor/axle as far BACK as it would go while gently rocking the forward worm gear head the opposite way, allowing me to engage the forward U-joint. I pushed the front of the motor part way in engaging the FORWARD U-joint, then rocked the REAR worm gear head back (making sure the joint was aligned) and pushed the REAR of the motor in, engaging the REAR U-joint as the motor slid into place.

    I then replaced the PCB by aligning the cut outs with the flywheels, and gently pressing down to engage the plastic tabs that hold it in place. I decided to replace all of the factory wires connecting the gear towers, motor, and PCB board (but NOT those for the LED... I haven't yet figured out how to access the LED, though I would like to replace the orange LED for a warm white LED).

    Before I put the shell back on (even before connecting the LED leads), I took the mechanism to my layout for a test drive. IT WORKED! SO I attached the LED leads, and "closed" the patient up...

    11-Re-wired and ready for shell.jpg

    To replace the shell, simply reverse the procedure used to remove it: Place the shell, install the two screws, replace the dome, and "re-latch" the handrails under the cab. Glad to have it running again... I plan to replace it's factory decoder with a Soundtraxx Tsunami 2 sometime early next year.

    I hope this helps anyone else needing to replace the motor in their Challenger!

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    Victor... I do think the motor brushes were too soft. When I first opened the loco up, there was red-brown powder (there must be something besides graphite in the brushes) spread all thru the motor recess in the chassis and all over the motor. I pulled the brushes out, and they seemed much too short for a motor that had probably only seem 50-100 hours of use. I though cleaning all the graphite powder MIGHT solve my problem... and it seemed to for 30 minutes or so, but then it all started again.

    I actually was able to scavange some brushes that are ALMOST the right size from another old motor, and installed them in the original motor from my challenger. RIght now, the old motor seems to be running OK, so I'll keep it in my parts box just in case. Tho', if the new Athearn motor fails, I might opt to try fitting a small coreless motor (tho' I worry about it having sufficient torque). This one comes with a 3D printed adaptor that looked to be about the right size to fit into the challenger chassis (and could be easily sanded to size): https://tramfabriek.nl/kato.html

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    Victor,
    Yes, I connected a different motor to the decoder, and the different motor seemd to run OK (for as long as I tested). So, the decoder seemed to be OK.

    What I forgot to mention, at one point when the factory motor was in its "shorted out" mode, I disconnected it from the decoder and clipped it to an old MRC DC power pack I have from 40+ years ago... the motor would not start, but if I gave it a twist, it would run until I turned the power off. When I re-applied power, it would not start until I helped it. After a few (helped) starts and stops, it might start on its own a few times, but then the issue would recur. Interestingly, I was holding it in my fingers during these tests, and seemed to feel some "roughness" to the motor when it was running after a helped start. When it was in a "remission," it seemed to run smoother.

    I did consider that the commutator might be getting bridged by the brushes, or powder worn off the brushes.

    I am embarrassed to say that my multimeter is also 40+ years old, and was a cheapie even way back then. So, I never really did look to see if the motor actually was shorted with my multimeter.

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    Hi NDave,
    k. that sounds like you have a good handle on the situation.
    the red/brown stuff is likely copper.... clean well to avoid electrical shorts... gah.
    yeah, those brushes have to be removed.... baaaad brushes!

    the coreless motor is interesting. the main reason I have not tested
    them is because I do not like the brushes and the lack of double ended motor shafts.
    the locos I am most interested in testing have a power truck on both ends.
    (I have an Atlas MP15 that could use a new motor...)

    victor

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    Yeah, most of the coreless motors I saw on eBay were single shaft. But, the one I linked was a double shaft, and the kit came with adaptors for 1.5mm shafts (pretty sure that is what the Athearn motor has), and the adaptor that looked like it could be adapted to the challenger. It did seem the motor speed was OK (for the record, I estimated the gear ratio for the challenger to be between 45:1 and 50:1, based on the # of turns of the motor to give one rotation of the drivers; based on the driver dia, I think I calculated a top speed between 60-80 smph, which is OK since I don't run over 40 smph)). I did worry about torque, tho'... In the end , I went for the quicker (aside from the 3 weeks for Athearn to ship the motor) solution requiring less engineering (engineering is not my strongest suit). We'll see how long it lasts this time... Just happy to have it running for now!

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    Reviewing this today... and want to mention an important step: after the new motor is finally in place, use fine forceps to push each of the intermediate U-joint pieces towards its worm gear, until you feel/hear them "click" into place. NOW you are ready to replace the PCB, connect wires, and test run!

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    Ya know, I think this forum is pretty blessed to have you, @randgust and @victor miranda. A wealth of knowledge about wee internal workings of N scale locomotives. ...
    Paul Schmidt

    Shasta (2008-2020) -- All good dogs should live forever

    Southern Railway's Slate Fork Branch

    Check out Appalachian Railroad Modeling!

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    Thanks. I feel like I am just a beginner, compared to Victor and Randgust... but want to do what I can to help others that might find themselves in the same situation I might be, whether it be swapping a decoder or a motor.

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    you are both very kind.

    it is a quiet determination to have a model ... well... simply run that got me involved in tinkering.
    ndave you are doing that on your own path.
    as long as a few are doing, taking photos, and sharing the surprisingly personal explorations
    our scale will grow.

    there is another skill aside from that and I think Paul has this skill.
    the ability to write and explain what was done and perhaps why the task was attempted.

    model trains require a broad range of skills.
    Many here have more abilities to create a layout
    and the scenery that is a full and complete model railroad.
    skills I have yet to set upon.

    victor

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