Loco motor "dead spot"?

[John_AP&W]

I just got a "vintage" Atlas S4 (DC only, their item #8285), and am having trouble getting it to run.

Followed Atlas shell-removal instructions. No decoder, just the original light "board"...

When DC is applied, the light comes on, but the motor won't turn UNTIL I give the armature a slight nudge with a small wooden toothpick.
Then it runs fine, and smoothly! As long as I don't shut off the power, it's just great!

After power is turned down, I'm back to no movement until the armature is turned a bit.

When powered down, the armature seems to ALWAYS like to come to rest at this "dead spot". I have yet to get it to stop at any other point.

I presume this has something to do with the brushes and commutator plates, but before I attempt to dig deeper, I thought I'd ask for input from the community...

What's the cause? What's the fix?

Thanks in advance for your constructive comments!
-John

 

[bnsf971]

You probably have a bad winding or open at the commutator.
The fix is to replae the motor, or return for exchange or refund if it's still in the return/repair window.

 

[Smudge617]

I just got a "vintage" Atlas S4 (DC only, their item #8285), and am having trouble getting it to run.

Followed Atlas shell-removal instructions. No decoder, just the original light "board"...

When DC is applied, the light comes on, but the motor won't turn UNTIL I give the armature a slight nudge with a small wooden toothpick.
Then it runs fine, and smoothly! As long as I don't shut off the power, it's just great!

After power is turned down, I'm back to no movement until the armature is turned a bit.

When powered down, the armature seems to ALWAYS like to come to rest at this "dead spot". I have yet to get it to stop at any other point.

I presume this has something to do with the brushes and commutator plates, but before I attempt to dig deeper, I thought I'd ask for input from the community...

What's the cause? What's the fix?

Thanks in advance for your constructive comments!
-John

Had the same problem, it's likely to be the winding, check if there's a loose wire (I used a small paintbrush alternating up and down to find it). Thats assuming you have a open case motor, but it is repairable if you know someone who refurbs electric armatures or windings, if not then it's a replacement motor, but I would just return it, unless you can't live without this S4.

 

[D&J RailRoad]

A replacement motor isn't all that expensive or difficult to install.

 

[tootnkumin]

I had an Athearn Genesis motor with the same fault. I eventually opened it up, after replacing it and found a loose wire on the commutator segment of one pole. Solder had a dry joint.

 

[trailrider]

Unless you can find a broken wire or loose connection, I'd search ebay for a duplicate replacement.

 

[D. Soppy]

You could try taking the motor apart and cleaning the brushes and commutator with brake clean or similar degreaser . After doing that check for sparking on the commutator when it is running. If there is excessive sparking , chances are one winding has opened up . A little grease or oil on the commutator will prevent proper brush contact and may cause dead spots. I did this to 2 of my 40 yr old locos and it solved the problem.

 

[Twinboystrains]

Replace the motor. Good for another 40 years.

 

[John_AP&W]

Thanks for all the replies!

Following the various ideas, I checked for loose wires, and any other faults at the magnets and windings...

I then flushed the commutator plates and brush faces with a small amount of isopropyl alcohol (ISA), let it evaporate, and tried running again.

Complete success! The loco now responds at a very low voltage, and runs smooth as silk. I can stop and re-start it with absolutely no hesitations.

Thanks for the suggestions, muchly appreciated!

-John