Problem with tender drive change to DCC

[RobinofLoxley]

I'm in the process of changing all my old locos to DCC or selling them. 

 

I've got a problem that has resulted now in 2 blown decoders. I have a suspect but would appreciate some feedback.

 

There are many variations of appearance of the Ringfield tender drives in terms for example of the motor brush retainers but as far as I know only 2 electrical variants; one where the power is carried on 2 cables (one from the tender wheels and the other from the loco via the post and collar connection), and the other where the power from the tender wheels is direct through the motor block, so only one cable. It's the second one where I have had trouble.

 

I followed advice to isolate the power feeds to the brushes by using plastic separators, clearly visible on the photo. I did this as the plastic screws I obtained didn't seem to fit correctly in the block. Power to the decoder was direct black from the post and collar, red from a soldered connection to the gear retaining clip in lieu of the engine block, again from advice here. 

 

After installation both times some short runs were done at low to intermediate speed on my test track about 1.2m long. No problems. The next time I tried it the loco was dead, and could not be revived.

 

I am guessing that I'm getting a short through the fixing screws but if anyone has a better idea please say! 

[Garside]

I think you have a short where the screws are fixed to the motor unless you have put tophat bushes through the brushes as I had the same problem converting a friends loco and used nylon screws to hold the brushes, had no problems afterwards.

 

regards Mike 

[newbryford]

Some ringfield chassis have a "hidden" lug from the main casting that presses on the rear of one of the brush tabs.

 

Look behind the tabs in the attached image.

 

[Brian]

As suggested check for a metal "Pip" behind the left-hand brush strips wiring tag.  Also ensure that tag cannot touch the metal of the Ringfield motor. Add sleeving over the wire and the tab as necessary.  

While you have insulated the screw head with the plastic, is the screw thread able to touch the left-hand brush strip still?  If so, this will cause a short and probably kill the decoder if not removed.  

Use a small piece of insulation or Heat shrink tubing over the top portion of the screw so as it isolates the screw from the metal brush strip. 

ALWAYs test the left-hand brush strip to all wheels and the metal of the motor BEFORE connecting a decoder.   Any connection noted while the testing MUST BE REMOVED before connecting the decoder.   Use a Multimeter set onto its Ohms range or its Buzzer function. Alternatively, use a battery powered buzzer and two test leads so as when the two leads are touched together the buzzer sounds, or use a lamp and battery and two test leads. The lamp lights when a conenction is present.  In all cases the Meter should read almost zero the Buzzer not sound or the lamp should not light. Testing one lead on the left strip and the other lead to all wheels and metal of the motor.

[melvin]

I no longer have tender drives. But when i did this is how i did it. 

I removed the brush holder completely and replaced it with an older type that did not have the screw type brush & spring retainer.Work fine.