I have 2 Atlas GP40s I've had for a long time. I hadn't run them in awhile and when I tried them, one didn't run while the other ran like new. So I disassembled it so the motor and gears sat in one half of the frame. I applied power and it turned with no problem. I put it back inside both frames without the trucks and applied power and nothing. The light comes on so it is getting power. If I spin the motor with my finger, sometimes it will run, but if I stop and try again, nothing. Same in either direction. I put both frame halves together with just the motor and flywheels and same thing. Jim
With what you describe, it sounds like it could have a bad motor pole. Had this occur with a couple units as well.
Power the motor up out of the loco, slowly, and grab the shaft or what ever is on the shaft and try to stop it. If the armature is good, the motor should still try to run as every pole passes. If there's an open or dirty commutator segment, the motor will stop pulling where it's bad. Doug
Hi Jim, You did not specify if you have the older style Atlas GP40 with the split light boards or the one piece light board? The problem I've had with Atlas N scale locomotives involves all models with the long single light board. I've found most of the time when the lights light, but the motor does not run is because of a poor contact between the motor leads and the pads on the bottom of the light board. I like to use a Cratex cleaning pad or Bright Boy to gently clean the brass motor leads. Important, when reassembling the locomotive make sure those motor leads are making a good contact with the pads on the bottom of the light board. Adding suggestion is trying Jim Kelly's method in the March 2019 Model Railroader N Scale Insight column. Jim soldered the motor leads to the bottom of the light board or in his case the bottom of the DCC decoder. A word of caution using this method, get in and out as fast as possible with the soldering iron, you don't want to accidentally un-solder components or damage the light board or DCC decoder by applying too much heat.
A word of caution using this method, get in and out as fast as possible with the soldering iron, you don't want to accidentally un-solder components or damage the light board or DCC decoder by applying too much heat.[/QUOTE] This is where you need to use a higher wattage iron. A low powered one means you have to stay on the joint longer, but a hotter one allows you to get on and off quickly.
It's the older style with the split light boards. The motor runs fine when just sitting in one half of the frame. After putting it back together and trying to test it again, it still did the same thing, I squeezed the motor towards the rear where it is just plastic, and it started. when I let go, it stopped. In doing this, I noticed that the motor moved a bit from side to side so I tilted it a bit and now it runs! Not wanting to tempt fate, I put the shell back on and I'm leaving it go. But if this occurs again, I will pay more attention to the contacts, possibly soldering leads to them (a last resort as my soldering skills are not up to par. I may do test soldering to get better, and buy a higher wattage iron, thanks Bill.) I did clean the motor contacts a bit but maybe it needs extended so it makes better contact with the frame. Thanks everyone for your suggestions. Jim
My Atlas/Katos have little black plastic spacers between the frame halves where the two bolts go. Could be those are squeezing together too tight on one end of the frame, causing the frame to touch the motor or a flywheel. Quick check is to back off the bolts a bit, wedge the frame apart a bit and see if that gets the motor to spin. I fixed this on one of mine by adding a bit of masking tape to the culprit spacer, increasing it's width (and the frame separation) by a couple of masking tape thicknesses.
The screws at each end shohuld be snug enough that the trucks don't fall out, but don't overtighten one or both or you might distort the frame. Maybe you could dissemble it and check frame halves with a straightdege.
Now it sounds more like the motor contacts are possibly making intermittent contact with the frame (assuming this is not a DCC unit). If this is the older type like it sounds like it is, if I recall correctly the motor contacts make contact with the frame halves as opposed to the underside of the light board as in the newer version. If there's not enough spring set in the motor contacts or they're too short or mal-aligned, they might not be making solid contact with the frame.
An update on my problem. As I said, it ran and I started running it. The other day, it stopped again. So today I took it apart and the metal contacts from the motor that touches the frame was my focus. I bent both top and bottom out a bit so it made better contact with the frame. I put it back together and it runs both directions starting at slow speed. I can't guarantee this is the final solution, but if it quits working after all this, it's going to my display area where all non working or poor running locos reside! (Hope it hears this threat and thinks twice about malfunctioning again!)
