Athearn Genesis GP-40L is surging at low speed

Model Railroader Electronics and DCC
1

Where do I need to start looking for the fix for my problem?

It is new, right out of the box, DCC, non sound.

Everything on the unit seems to work, and this is not my first DCC loco, but it is the first one I have bought that has this low speed surge.

It does get slightly better as the speed increases, but I really like to operate in the low speed range for realism.

I have not taken anything apart at this point, but I have done my fair share of work on HO locos in the past.

Could it be mechanical (ei, lack of lube in the trucks?) Or electrical, as in needing an adjustment to the CVs?

I’m an open book, so I bet a nudge in the right direction from the more veteran modellers here will lead me to a solution.

Thanks for your help.

2

Do you know who’s decoder is in the unit?

3

No I don’t, without looking it up. It’s whatever Athearn installed from the factory.

4

I think I’d start with a decoder re-set. Sometimes that clears up lots of little glitches.

Mike.

5

I’ll say both. It’s brand new, you might need to run it in a while. But check the lube, it could be completely dry OR as is often the case, there’s way too much grease in the gears - too much can be just as bad as none.

At the same time, motor surge can also be because of badly adjusted back EMF settings. As the decoder tries to speed the motor up, it goes too far, and then tries to slow it down - and goes too far, makike a surge back and forth. Not sure what decodrs they are using in those, and what adjustments are available to help adjust this, but definitely give it some run time first.

–Randy

6

I agree with Randy my last new Walthers GP30 had so much white grease stuffed in the bottom of the trucks it varied the speed as much 11 scale miles per hour per lap.

The plastic cover on the bottom of the Genesis locos are very easy to remove. Just make sure it is upside down and be carefull of all the detail parts. I use an old Bowser cradle.

SB

7

Try loosening the four motor mount screws. I’ve seen a couple cases where what you describe has happened when the motor cradle was screwed down tight causing the cradle to put a slight bind on the motor.

Maybe … maybe not … but worth a shot.

Mark.