This one is a bit oddball but it’s the only thing I can come up with. Has anyone ever heard of an Athearn BB underframe shorting out? I have a BB F7A that I got from my uncle. It has plastic sideframes, flywheels and a gold side motor as to the era question. It doesn’t want to run on track and has shorted out the pack a couple times.
In attempts to debug the short, I have tried a different gold side Athearn motor and replaced a truck (with the other one removed completely) with a truck from a working F7. The only components that weren’t changed out for testing were the underframe, the flywheels, the rest of the driveline components, and the connector strip. (Yes I still use those.) The couplers are Kadee 140 series with 252 boxes (30 series equivilents for the 140 series couplers) so the couplers aren’t the problem either.
I have run this problem through the Athearn FB page and everything that was suggested there has been checked and ruled out (except for installing a Kato motor instead of the Athearn one which I don’t think is the issue). I am totally stumped as to what the problem could be other than the frame. Any other ideas would be most welcomed.
Make sure it has not had two front or two rear truck installed by mistake. This will cause a dead short.
The vertical parts of the inverted “L” shaped electrical brackets on the trucks should both be on the same side. If they are on different sides you either have two front of two rear power trucks.
I have a number of BB engines, even a couple of “neutered” rubber band drive ones. It’s critical to examine the trucks, as has been suggested, to make sure they are installed correctly. Also, remember that the chassis is actually part of the power circuit.
The tool you need is a multimeter. That will let you quickly isolate the short. Get a few alligator clip leads while you’re at it.
Another easily overlooked problem could be the couplers. My old Athearns had the coupler boxes cast as part of the chassis, so they were also part of the electrical circuit. If someone replaced the original plastic couplers with metal ones like Kadees, that could leave the engine with hot couplers, and coupling two such engines together would result in a short.
You need to get your detective hat on. First thing I would do is lift one truck, leave the other one on the track, and see what happens. Do the same with the other truck. If the short stops in one of these cases, then the truck or wheels are at fault. I suspect that some non-original parts have been used, a misassembly, or a warped piece of equipment.
As someone else mentioned, check if the short happens on the curves, straight track, switches, etc. You might want to try this with the body removed. A short on a curve suggests that a truck is shorting on the frame, or something under the body.
Haven’t tried removing the connector clip. I’m pretty sure the truck bracket isn’t touching the frame as this occurs on a straight section.
The trucks are on the same side so it’s not that. (I crossed the trucks on a pair of GP9s before however.)
I removed the bracket to check it on another working F7 and found the light bulb itself was burned out. The unit still shorted without the bracket.
[quote user=“MisterBeasley”]
I have a number of BB engines, even a couple of “neutered” rubber band drive ones. It’s critical to examine the trucks, as has been suggested, to make sure they are installed correctly. Also, remember that the chassis is actually part of the power circuit.
The tool you need is a multimeter. That will let you quickly isolate the short. Get a few alligator clip leads while you’re at it.
Another easily overlooked problem could be the couplers.&nbs
Since every component has been swapped out and tested with known working ones, that leads me to the frame itself. Either a spot where paint has worn off around the trucks or motor allowing a short, or a pesky small burr in tose areas going unnoticed. The last thing I would to do other than closely examine the frame is to assemble all the parts on a working frame and see if the issue moves over with the parts. If that proved no issue. And the frame and insolpaint checked out. Time for a new frame. Or becomes a shelf or back shop parts piece. Outside of that, I am stumped to. That athearn has such a simple electrical circuit.
Question about the nature of the short itself. Is this an instant short as soon as you put it on the track or can you get some running distance before it shorts?
Athearn motor mounts I have dealt with are not cast into the frame.
They are rubber or plastic pads that slide onto the bottom of the motor and are press fit or held in place by screws.
If the motor mounts are cast into the frame you might be dealing with a Bachmann unit.
The diagram shows the motor mount pad(s); part(s) #80426 and the screws that hold them in place; Motor Mount Screw #84027.
If the motor is not isolated with these motor mount pads then it will short out to the frame.
Also, the bottom brush clip on the motor has two (2) progs that provide an electrical path from the frame to the motor.
When isolating the frame these prongs need to be pressed back into the clip, filed off or the top clip can be cut where it clips onto the motor and swapped for the bottom clip with the progs.
I don’t see how the frame can be shorting. It’s a hunk of metal, so certainly if checked for continuity there won’t be much resistance found.
To have a short requires at least two components and continuity between them, so there has to be something else involved. The fact that the “something else” has not yet been identified should not lead to a conclusion that the frame is the issue.
After reading through this entire thread a couple of times, I come to the same conclusion as Mr. B. You need a multimeter to isolate the short and eliminate the guess work.
Only time I have seen something like this was on a second hand item where they changed out a screw and put in one way too long that it shorted out the item.
Sit the engine on the track with the shell off, turn off the room lights so you are in the dark, wait a little while for your eyes to adjust, turn up the throttle and see if you can see the arc/spark at the point of the short while you are waiting for that mutimeter to arrive from Amazon. Don’t ware out your overload protector.
I finally got my multimeter and started doing some continuity testing on the engine with one truck attached (no motor inserted) as well as the individual parts themselves.
What I have found is this:
The motor separately itself shows no continuity from top clip to bottom clip. (which I expected.)
The frame shows continuity from the metal strip the bottom motor clip sits on to the posts where the trucks sit. (I didn’t expect that so I checked the frame on one of my “working” units and it did that same thing. Given the way the motor works, I always thought that was separate.)
The tower on the truck shows no continuity to the frame. However, when the light bracket is connected, it does show continuity.
The other side of the truck shows continuity when I check it on the light bracket. With the bracket off, it still shows continuity to the light bracket mount.
The light bracket didn’t do anything to the unit that works.
