Hi forum.

I have been helping my mom sell some of my late father's large Marklin train collection. I have been helping her test, cleanup, and fix the various engines and cars, but have run out of ideas on one specific model.

So we have 3 identical model 3649 ABA Electro-Motive engines that I cannot get to do anything. What is bizarre is that, well... we have 3 of these units and they all do not work. Super weird?

I am using a 6021 digital controller, and in the manual for it it shows the dip switch address settings, so I can look at the digital chip and can tell what address each is supposed to be... But the units do not respond to anything, not the "function" command (to turn on and off the light) or to any speed settings.

But, when I reset the controller (by holding the GO and STOP buttons at the same time) they sort of "jump" forward an eight of an inch or so. So this tells me they are getting power of some sort, and the motors are still working.

I am struggling to find any troubleshooting guides or information on this model, so any help would be appreciated! I am pretty good with a multi-meter, so any tips/tricks or ideas would be much appreciated!

Many times with these old decoder, the contacts for the individual dip switches get corroded. If you cycle "on an off" all of the dip switches 5-6 times, it usually cleans the contacts.

Rick

Hi,

Just a basic question how are you sure that the motors are "working"?
Just because there is a little "jump" when you reset the power? ?
Or because you have applied power directly to them? Never a good idea in a loco with decoders!

If my memory serves me well 3649 were using a special "booster" board in the B unit , in order to provide enough 'juice' to the power hungry DCM motors.
Let's try to proceed with a diagnostic first , rather than trying "shots in the dark" solutions...

As a starter, could you remove the 3 bodies of the loco and provide us with close up pictures of the top of the chassis , insisting on the wires and connections on the various components? (motors, decoders, booster , light fixtures)

We'll get to the bottom of this one, like always!

Cheers

Jacques

Thanks for all the suggestions and posts all!

I have bodies off all of these. I have taken some pictures and posted them to my good drive. Link is here: https://drive.google.com...nFGkmMV9sMv9V2QNfVHrH1pX

Hopefully you can all view the pictures there.

I tried moving the switches about 10 times each on one of the units, but no difference. I'll try it on the other two to see if they work.

I have not jumped power to any motors. The units just "jump" ( I meant move a tiny bit forward) when I reset the digital controller. The motors spin freely if I just spin the wheels with my hand, I have added more oil as well to help lubricate them.

I believe I am reading the dip switches correctly, the first position has the ON clearly labeled. Just in case I'm not, I did go through all 80 addresses and none of them worked!

The default address for this loco is 07 (2, 5 and 7 on) (because it is an F7 loco, the default address for many locos originally is their class number).

Hi
Chances for all 3 units to fail simultaneously are very small
Likely motor are jammed by old oil as Jacques already mentioned. So remove the brushes and try to rotate gently the driving wheels. Do this on all motor engines. If they all rotate then problem is elsewhere. Don't forget to install back the brushes.
One sad possibility though: if you have left the motor with power on and the order to rotate when it is seized then burning of the motor(s) or of the power transistor is likely after a few seconds (10? 20?)
Cheers
Jean

Ah, great to hear there is success. The clue to me was that all three identical locos wouldn't respond.

Later decoders are designed to deal with either polarity so that they could be used in G1 where the polarity cannot be set (this is why very early G1 decoders use an early form of DCC) because the signal is transmitted through the two rails only without a centre stud.