Loco only runs in reverse - issue not with the track

[John-3751791707823374]

Hello Everyone,

I have a Hornby 0-6-0 DC model which is a couple of years old, it has been boxed and not used much since I got it.

It was running fine before, but now it will only run in reverse. Other locos will run in both directions so it isn't the track or power. The layout is DC.

I thought I spotted a very small amount of smoke from the loco, just a small amount for less than a second. But as I said it still runs fine in one direction. Any ideas on what the issue could be ?

[P-Henny]

Probably to do with mechanical physics. When a motor turns it generates torque. This torque is applied to the drive train and wheels and anything connected to them. When the motor reverses the torque applied to the moving parts reverses too.

What may be happening is that in reverse all is well, but when put into forward the reversed torque is moving something due to play created from wear & tear that is critical to the electrical path to the motor, like the wheels connected to the pickups for example or perhaps the motor brushes.

With the body off, apply the wires of your controller directly to both electrical connection sides of the motor. If that allows the the motor to turn in both directions, then inspect the pickups and re-tension them if deemed necessary.

FYI as a first time poster. Note how my paragraphs are closer together than yours with smaller gaps. That is because the forum software automatically adds paragraph gaps to the ones you inserted when writing your post. You can use the 3 dot menu edit function to remove your excess 'carriage returns' and make your post display like mine.

[John-3751791707823374]

Hi P-Henry,

Thanks for your reply. I've edited my post and will remember in future.

Any thoughts on the small amount of smoke and slight burning smell from the loco ? Could something electrical have burnt out to cause such an issue as this ?

[P-Henny]

A burn out would normally be all or nothing. Still working in one direction kinda puts a different perspective on things.

If it was a 'winding coil' cooked issue I would have expected both directions to be affected, but I'm completely open to any alternative views & thoughts of others on here.

[Simon-372339]

What model is it (R number on the box if original).

Remove the body.

Depending upon the model you should see a drive gear on the motor shaft, this will turn the wheels.

Rotate this by hand does it move freely in both directions?

[P-Henny]

Simon's reply has triggered a thought.

In forward direction the loco doesn't move but can you hear any buzzing or other electrical noise as if it is trying to move. It may be a physical problem as per a variation of my intial reply where the torques are locking up the drive train & gears when trying to go forward due to worn parts. This would create the motor to draw what is called the 'stall current'. This current is much higher than the normal running current and will generate heat. If left in the 'stall condition' for more than a few seconds then permanent burn out damage in the motor windings can result.

[ntpntpntp]

I'd suggest have the bodyshell off, look over the mechanism for any obvious faults such as a loose or split gear. Test the mechanism under power with the body off so you can see if there is any slight movement before it locks up?

Is it a sealed can motor? I've come across N gauge sealed can motors where the brushes are "fingers" of precious metal rather than the traditional carbon brush: if these fingers break or wear it can cause jamming of the commutator in one direction and requires a replacement motor. It might be worth removing the motor and testing it, you can even check for this sort of brush problem just try turning the shaft by hand while the motor is out of the motel. You can also check the rest of the loco geartrain moves freely and doesn't lock up.

It's not a model with a decoder fitted is it? They do generally work on DC. If the decoder blows one of its motor drive transistors this can cause one-way operation.

[Rana Temporia]

I had this issue a couple of years ago and in my case it was due to the carbon having fallen off one of the brushes. When going in one direction the brass brush arm was fine as it was dragging across the commutator. In the other direction it dug into the gaps in the commutator and jammed the motor solid. If yours is a sealed motor I’d take it out of the chassis and try it to see if it rotates in both directions, and while the motor is out I would check if the chassis rotates in both directions. It may be a pick-up jamming in the wheel spokes in one direction.

[5Dublo2]

I had a similar issue some time ago, loco worked in one direction and would slightly move in the opposite direction and then stop.

When I took the body off I found out that the position of a wire was fouling the worm gear - in one direction the worm pushed the wire out the way, in the other direction it pulled the wire up the worm to jam against the drive gear causing the loco to stop. Reversing the direction again then freed the wire and the loco moved.

If something similar is happening to you then the loco will move slightly before it stops