Atlas pickup woes

[shark_jj]

Hi gang, I tried searching for the answer to this since it is such a common problem with Atlas locomotives with no success.  I may not be asking the question right in my search.  Anyway, I am working on an Atlas SD35 which has inconsistent pickup.  So far, I have cleaned the brass strip which conveys the power from the wheels.  I have put little dabs of solder on the 4 pads of the decoder so the decoder is a tight fit.  Still getting inconsistent pickup.  If I push down gently on the centre of the decoder, voila, constant pickup.  Since the tabs are tight enough I have to push them in, I am looking at the two contacts on the underside of the decoder, which off course you cannot see once the decoder is in place.  I have bent the two copper strips up slightly to make sure they are reaching the board.  I have looked at the alignment with the board out and placed vertically where it would be located and the alignment seems to be ok.  When I put everything back together, it will run for a few inches, slow down, then speed up, then stop, then start, and so on.  Push down on the centre of the decoder and off she goes running consistently.  Appreciate any thoughts.

[wcfn100]

Whenever I break out my stuff, I pretty much always need to clean the axle point pockets in the side frames and the tab on top of the trucks that contacts the strip.  I just had an IMR FT that I actually had to file the top of the tab because stuff was so caked on.

Jason

[shark_jj]

thanks Jason, good suggestion, I cleaned them when I cleaned the brass strips.  Because I get contact when pressing down on the centre of the decoder, I am pretty certain, this problem is located at the decoder.

[wcfn100]

I guess I should back up one step.  The first thing I do is put the loco on the track and check continuity from the rail to the frame with a volt meter.  That will tell me if it's the pick up or something with the board.

Jason

[randgust]

Try wrapping a rubber band tight around the chassis to hold the decoder tighter on the frame.   That will prove whether it is axle contacts, wipers, wheels...whatever...vs an actual contact issue with the decoder.

[shark_jj]

11.5 volts on the rail.  11.5 volts from one rail to top of frame, both sides.

[wcfn100]

Do the lights go off when the motor stops?


Jason

[shark_jj]

the lights go off when the motor stops.  I ran the loco until it stopped and then checked both sides of the frame.  Zero voltage.  That would point towards the pickup on the wheels.  What is weird, is that while it is sitting their stopped, without any action on my part, the light will go on and it will start running again.

[wcfn100]

Okay, then I'm probably out of ideas.  FWIW, the FT a mentioned before was doing the same thing where it would slow down and stop (lights out) and then start up again after a second.  It ended up being the contacts, but more specifically the tab contact on one of one truck.  Maybe instead of the checking continuity from the rail, do it from each wheel to the frame. 


Jason

[shark_jj]

Jason, you sent me on the right track.  I put a paper between one truck and the rail, and the remaining truck picked up power.  Reversed it and the other truck is not picking  up power at all.  So, this process has identified that one truck is not picking up power, so I will work on solving that problem. 

[wcfn100]

Cool, I hope you find the issue.  On my FT, I cleaned out the pickup cones with a toothpick soaked with alcohol and as I said before actually had to file down the top of the pick up tab on one side it was so dirty.  Hitting it with some sand paper wasn't enough.


Jason

[Big Train]

I had the same problem with an Atlas SD-60. Same symptoms. Press down on the decoder and it works. Ended up hardwiring jumpers from the motor contact strips to the motor pick up pads on the underside of the decoder. Did have to trim the contact strips back a bit and apply kaption tape on the frame as a preventative thing. Works fine now.

As to why this happens, I dunno. I think sometimes it's just quicker to find a work around and get back to running trains.

Hope this helps.

[peteski]

I had the same problem with an Atlas SD-60. Same symptoms. Press down on the decoder and it works. Ended up hardwiring jumpers from the motor contact strips to the motor pick up pads on the underside of the decoder. Did have to trim the contact strips back a bit and apply kaption tape on the frame as a preventative thing. Works fine now.

As to why this happens, I dunno. I think sometimes it's just quicker to find a work around and get back to running trains.

Hope this helps.

The poor contact between the motor contact strips and the metal pads on the decoder is a very common problem in these models.  One possibility is that when the motor contacts get deflected when the decoder is installed, they slip off the contact pad causing open circuit.  But this problem is different than the intermittent contact between the rails and the decoder.  The loco can actually exhibit both problems (motor and rail contact issues), and both have to be addressed for the loco to be reliable.

[Joetrain59]

Ive been surprised at how many times I discover a loco is picking up power from only one truck. Usually when cleaning wheels. A thorough cleaning of truck tab, axle points, and very light polishing of contact strip on frame. Sometimes need to bend contact strip down more.
 Joe D

[Santa Fe Guy]

Many years ago I found that the decoder in an Atlas SD60 would bow and loose contact once the body was fitted.
So long back cannot remember what I did to solve the issue.
Rod.