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Atlas RS3 DCC installation short

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Atlas RS3 DCC installation short
Posted by BigDaddy on Thursday, June 14, 2018 4:20 PM

1980's vintage, made in Japan HO loco.  I checked the current draw, it was less than 1 amp.  Installed a basic NCE decoder and it ran a couple minutes and died.  The decoder could not be revived. 

Sent the decoder back to NCE with a check, they sent me a new one.  Installed it and blew another decoder.  Put it on the shelf and went on to do other installations successfully.

Decided to revist this one.  The engine sits in 2 piece of plastic.  The lower motor brass tab does not contact the mounting screw.  Would the brass tab contacting the side of the engine case cause the short.   The brass tab is attached to the wire with the white shrink tube.

Henry

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Posted by tstage on Thursday, June 14, 2018 4:40 PM

Henry,

Did you probe the chassis/motor brushes for shorts with a multimeter before doing the decoder installs?

Tom

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Posted by BigDaddy on Thursday, June 14, 2018 4:53 PM

tstage
Did you probe the chassis/motor brushes for shorts with a multimeter before doing the decoder installs?

I did, especially after the first debacle.   There was nothing.

Henry

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Posted by tstage on Thursday, June 14, 2018 4:59 PM

Did you insulate the bottom side of the decoder so that none of the pads or wires contacted the chassis?

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Posted by BigDaddy on Thursday, June 14, 2018 5:25 PM

No Tom, but the decoder was one of those replacement style decoders and snapped on tabs on the plastic motor mount, without touching anything. 

I should add, I also had a Roco Atlas RS3 and put a loksound into it without any problems.  The Roco used an Athearn style motor mount.

Henry

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Posted by richhotrain on Thursday, June 14, 2018 5:36 PM

Isolating the motor is only part of the task to convert a DC loco to DCC. To avoid frying the decoder, you need to totally isolate the brushes from the frame and any other metal parts. You not only need to directly isolate the brushes but also indirectly by insulating metal tabs and grounding wires. That wire running from the brass tab is suspicious.

Rich

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Posted by BigDaddy on Thursday, June 14, 2018 6:20 PM

richhotrain
You not only need to directly isolate the brushes but also indirectly by insulating metal tabs and grounding wires. That wire running from the brass tab is suspicious.

The wire is the gray wire, it might look like a bare wire in the pic, but it is not.  The motor mount screw does not extend beyond the plastic motor mount so it is not contacting the lower brush and the motor sits in the plastic motor mounts, so the motor is not contacting the frame nor the bottom of the decoder. 

The brass tab doesn't contact the frame either, but can touch the motor case.  Is that the problem?

I believe it is an NCE 106 DA-SR decoder. Peak draw for the engine was .95, the decoder is rated at 1.3 continuous, 2 peak

Henry

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Posted by rrinker on Thursday, June 14, 2018 8:32 PM

 Something would have to be broken for those Atlas/Kato RS3's to short anything out. Neither motor brush is grounded to the chassis, both motor leads come up to the top and are clamped under the two long rods going front to back on that plastic board. Each truck has a pair of leads that clip to the respective ends of those rods. The headlight also has its leads pinched between those rods int he middle of the plastic board, and it shines into a pair of light tubes mounted to the shell for the froont and rear lights. Pretty simple construction. Something has to be broken or altered if the motor brushes are contacting the track pickups - even thr trucks aren;t grounded to the chassis on these.

                              --Randy

 


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Posted by BigDaddy on Thursday, June 14, 2018 10:31 PM

rrinker

 Something would have to be broken for those Atlas/Kato RS3's to short anything out. Neither motor brush is grounded to the chassis, both motor leads come up to the top and are clamped under the two long rods going front to back on that plastic board.

Each truck has a pair of leads that clip to the respective ends of those rods.

The headlight also has its leads pinched between those rods in the middle of the plastic board, and it shines into a pair of light tubes mounted to the shell for the front and rear lights.

The plastic board has been replaced by the decoder.  The headlights are now LED's attached to the appropriate pads on the decoder.  The long rods are gone and the motor leads and truck leads are attached to the decoder. 

In a derail situation the trucks can't hit the frame.  It ran fine on DC before the conversion.  What could be broken?

This pic is from a previous thread before conversion

Henry

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Posted by Anonymous on Sunday, June 17, 2018 4:40 PM

Have you tried placing the chasis on a piece of track and checking continuity between the motor leads and the rail (without a decoder installed).

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Posted by bandmjim on Sunday, June 17, 2018 6:48 PM

When doing this install I solder wires to the motor leads, cut the motor leads short enough so they cannot contact anything, esp. the lower lead so it will not touch the upper motor brush area and then using kapton tape I tape both leads tight to the motor which should insulate those leads from any possible contact with the decoder.

Also check with multi meter as others have suggested as something is causing a short.

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Posted by wjstix on Monday, June 18, 2018 4:20 PM

Not sure about NCE, but many light-board replacement decoders have the motor connections on the same side, rather than one on each side as appears to be the case for the lightboard in your picture. This means you have to solder a short section of wire to one of the brass leads and run it over or under the decoder. Be sure this is totally insulated so that it isn't touching the decoder except where the wire is soldered to the decoder. Also, maybe put down a piece of tape on top of the motor to be sure the uninsulated bottom of the decoder isn't touching something there.

A good test is to (sorry) open the engine back up, and un-snap the decoder so it's sitting up a 1/4" or so, but the wires are all still connected. If it works then, it means there's a short caused when the decoder is snapped down in place.

Stix
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Posted by rrinker on Monday, June 18, 2018 5:19 PM

 What I do with them is similar to what bandajim mentioned. I cut the brass strips coming from the motor short, and solder on some spare lengths of orange and grey wire, So what crosses the top of the motor under the decoder is an insulated piece of wire. I keep all cut-offs from installing decoders for such purposes.

                                      --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by BigDaddy on Monday, June 18, 2018 5:20 PM

 I can see no connection between the trucks and the metal chasis. In a derail, a wheel might touch the chassis but I can't see how an opposite wheel would touch the chasis too.

The motor is mounted in plastic.  No part of the motor, or the copper tabs to the brushes can contact the chassis. 

The old decoders where removed.  I was a aware that a bare part of the motor lead touching the decoder would be bad.  I don't think I would have missed that.

I've installed a new TCS decoder, and frankly I'm still building courage to put it on a live track as none of the suggestion so far have given me a "doh" moment.

 

Henry

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Posted by rrinker on Monday, June 18, 2018 10:04 PM

 Try the program track first. The low current SHOULD keep it from frying. If you can't read or write it, there's a wiring fault somewhere.

 TCS motor decoders need no special program track booosters or any of that stuff to work, so it SHOULD work. If it can program and read back, only then try it on the main.

                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by richhotrain on Tuesday, June 19, 2018 4:12 AM

BigDaddy

I've installed a new TCS decoder, and frankly I'm still building courage to put it on a live track as none of the suggestion so far have given me a "doh" moment. 

If I fried two decoders in quick succession on the same loco, I would not try a third one until I was sure that I had resolved the problem. You need to find the source of the excess current that is frying decoders.

Rich

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Posted by BigDaddy on Sunday, August 12, 2018 5:08 PM

Time to stick a fork in this thread and let you know  :stupid:

(There should be a little gif there, that I can see, but if you cannot, it says I'm with stupid.) 

Nothing happened with the new decoder, as in no movement, no decoder detected, nothing.  Ashamed, embarrased and hacked off, I almost threw it in the trash, but that would violate my pack rat gene.

There was a thread about testing/programming a decoder, without hooking it up to a loco.  Randy said the decoder needs to detect the motor to work.  Eventually that percolated in my brain and I bought an Atlas motor off ebay.  When I took the old motor off, the brush spring was half hanging out of the little clip that retains the spring.

This clip kept coming off when I was installing the first decoder.  This was the same time I was having trouble with a secondary cataract in one eye and a primary cataract in the other, so I never saw the spring.  Probably I never fried a decoder, the loco, worked for a short while with an inadequate spring then quit.

Henry

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Posted by jjdamnit on Sunday, August 12, 2018 5:31 PM

Hello all,

First, my condolences of the loss of the previous decoders.

Personally I have never liked or trusted the snap-in PCB type decoders. 

Realizing that you have done a meter-trace of all the possible circuits I would suggest switching, if possible, to a decoder with a harness. 

This will allow you to solder and meter-trace as you go.

Good luck and...

I hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by BigDaddy on Sunday, August 12, 2018 5:33 PM

I did return one to NCE, but it was all in the motor.  No decoders were harmed in the process.

Henry

COB Potomac & Northern

Shenandoah Valley

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