DCC On Board GP40 problems

[scrimjimmy]

Hello,

I have a Bachmann GP40 with the DCC on board decoder that has a odd problem lately. It runs fine under DCC except going down grade with a train behind it. Then is seems to surge, speeding up and slowing down real jerky. Going up hill no problems. just down hill. Any clues what I should look for to get this running smoothly?

Jim

[Frisco]

It is being pusted by the train. Many older(and some newer) locomotives have this problem.I am not sure if there is anything you can do to fix it. Some-one else may know more.

[Running Bear]

I have the same problem with all my locos that are equipped with Bachmann decoders. The only ones that don't do it are those that have decoders with BEMF.

[Yampa Bob]

Negative loading is a real world problem in physics.  Consider a semi holding back a load downhill on a 7% grade.  Every time the brakes are pumped, the truck slows, then surges ahead when the brakes are released.

I don't know if this applies, but the new Digitrax DZ125 has "cruise control".  Perhaps that is their version of back EMF.

[pdlethbridge]

usually when I have a problem with back EMF, people leave the room holding their noses.

[Yampa Bob]

The scientific name for that is "Emitting Major Flatulence", very popular in crowded elevators or in the meat aisle.

[pdlethbridge]

  I'm banned from using elevators!

[Jim Banner]

Now that the air has had time to clear, lets get back to Jim's surging problem. 

I think the key word is "lately."  It implies something has changed.  While this could mean that the motor has worn itself a little more end play, the most likely thing is that the locomotive needs lubrication.  A tiny drop of light oil at each end of the motor would be the first thing to try.  Use a light weight, plastics compatible oil such as Labelle 108.  Also use light oil on the shaft bearings in the gear towers and on the axles in the trucks.  For the gears themselves, use either a plastic compatible gear oil or gear grease.

Now back to the boys who are dueling it out in the reading room of the local library.
Oh my!
Somebody just offered them pages torn from an old catalogue.

[grumpy]

An Eaton's catalogue I am sure.
Don

[pdlethbridge]

Jim, if I use oil, I get bubbles, lots ans lots of bubbles I really hate it when there is liquid in my gas, solids aren't as bad, but liquids,,,, watch out!

[Yampa Bob]

Eeeeeeewwwww!   

[Running Bear]

Eeeeeeewwwww!  

I agree.

[pdlethbridge]

Bob?  Eeeeeeewwwww!     Like you've never had that problem.

[scrimjimmy]

Hello All,

After further looking into this problem I have it fixed. I took the loco apart and found there was enough lube on all the gears. What I did notice when looking at the motor was that there was wires going under the motor and they are connected to some resistors. This had me puzzled. So out came the motor and underneath I found 3 little yellow caps on the motor. 1 across the brushes and 1 from each brush to the motor case. Well a light bulb went on in my head and I remembered how you have to cut the yellow caps off the boards on the Spectrum steamers for DCC operation. Well I cut all 3 caps off and now the loco runs very smooth with no chugging going down hill. Problem solved. I have a feeling this is a fix for all DCC onboard locos.

Jim

[steve turner]

Glad you got it running! Many DCC sites tell you to remove those capacitors, they are for electrical noise interfence prevention requirements in many countries especially Europe.Im assuming because Bachmann sells world wide they include them as per regulations on all their product lines!Removal of the yellow buttons some locos having one or two or as you state 3 improves slow speed operation of the loco with a DCC decoder. As mentioned by others steep grades with gear lash certainly is the major cause of lurching on a down hill grade .Some guys have far to steep grades that does not help the situation.The othe factor is the weight and number of cars behind the loco.