StrathpefferJunction

Thanks for the input, folks. I'll have another look at it tomorrow.

My bench power supply is a proper electronics power supply, through which you can adjust voltage and current.

It is probably something a bit sticky in the drive train causing surges of excessive current draw.

 

When on DCC the power to the motor is a much lower impedance source, so if the motor needs more current the decoder just supplies it.

 

On DC if more current is required it has to be supplied by the controller, and if it is a correctly tuned feedback controller it might make a good feast of providing it, but for the most part the power will either be limited (variable resistance controller) or fixed (PWM or variable transformer controller) and the motor will just slow.

Thanks, Suzie. 

I'll definitely have a look at the worm screw and the rest of the drive train to see if there's an issue there. Will see how I get on! :-)

Hi folks. 

I have a Bachmann Class 37 (21 pin) loco that runs poorly with speed (and current) surges on DC, but seems to run OK on DCC (albeit a bit noisy). Normally, it's the other way round that you find running problems, so this one has me a bit stumped. 

I have isolated the motor and is seems to be ok running from DC from my bench power supply. I have also ascertained that the pick ups are OK and power is getting to the PCB ok. I have tried different DC 21 pin blanking plates, so I don't think that's the problem. I can only assume that there's perhaps a fault with the PCB or a component thereon, but I'm electronics knowledge is at its limit on all of this! 

I have also run other Bachmann Class 37 units on the same dc controller, and they run fine, so I don't think it's the dc controller that is at fault. The problem loco also runs reasonably OK on dc in reverse, but the regular but random  power and current surges happen in  forward direction and make running the loco forward all but impossible. 

Has anyone ever come across the before or has an idea what might be going on and how I might be able to fix it? Could it still be a motor issue? 

Many thanks indeed. :-)