Atlas GP-35 with TMCC Locomotive all of a sudden just up and hauls A_ _ for some reason

I had a Lionel TMCC that did the same thing. Turned out the magnetic ring on the motor cracked and came off.

I had two options; replace the motor or add ERR cruise. The motor looked like a total pain so I opted for ERR cruise on mine.

Good Luck!!

Depends what specific system you have in the Atlas, but does sound like the cruise control section failed, in some manner.   Or if this was non cruise DCDR, a triac may have shorted for full voltage to motor.  G

For what it’s worth, I recently had a similar issue with an Lionel TMCC F7 I purchased and finally put on the tracks this week using a CAB1.  Given your unit is Atlas with Lionell TMCC not sure if this will help.  I had to disable the Odyssey speed control, reset the “steps” to low and the engine is working fine now.  Are you able to do the equivalent with your engine?

I have had the rocket syndrome happen a few times on my layout. The first was with an AC Commander, the train was running fine and all of a sudden it took off, that happened twice and I removed the board and put that one back to conventional. I have had it happen in a second locomotive with the AC Commander, and just of late with a Cruise Commander. Not sure of what is the cause but with the Cruise Commander I shut down the power on the layout and rebooted, than tried starting the Railsounds, if the sounds come on the locomotive us fine, if not when I start the locomotive, rocket time. I don't know the cause, it's intermittent.

Ray

For Atlas with the TAS EOB, this is very common.  Many times a wire to the tach reader breaks right at the motor.  If it takes off when you first crack the throttle, then that's my top suspect.  If it takes off when you apply power, then I'd lean to GGG's reasoning that a triac/FET has failed.

If it has EOB (box label should say TMCC by Train America on it somewhere) you could disable cruise with the following keys:

ENG + ## + DIR + AUX1 + AUX1 + AUX1 (whistle/horn blast will sound) + 3 (whistle/horn blast will sound again)

If it runs with cruise off, you could investigate the encoder for a thrown tape or a slipped sensor, broken wire, etc. Atlas may or may not have used a striped tape, my old NYC F2s had a machined grooves in flywheel that were painted black.   

Good Morning,  I want to thank all of you, JeffT, GGG, VJandP, Rayin "S", GRJ and Norm Charbonneau, for your great answers.  After reading thru your answers and after Christmas, too many Honey Do's to do trying to get ready for having all of the family here for Christmas is keeping me very busy.  As soon as things settle down, I will get the unit back out of my storage and pull the shell off and see what I can come up with, I'll also take pictures (I probably should have done that in the first place), then maybe someone can tell me exactly what I'm looking at and I can go from that point.  I really want to get it fixed as I run it quite often.  My problem right now is its been many many years since I've done trouble shooting and I don't know enough about the components in this part of the hobby to be able to fix my own trains but I really want to learn how.  Thanks again, see you all soon.