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Very unusual Decoder results after DCC install. Please help.

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Very unusual Decoder results after DCC install. Please help.
Posted by irishRR on Tuesday, July 10, 2018 9:54 PM

I just had a very unusual experience with a Digitrax DCC drop in decoder install. I have successfully installed over 10 decoders in my other locomotives (both drop in and hard wired), but this is weird. After installing the decoder, I was performing a test. Immediately I sensed something was wrong. The loco still buzzed as if it was DC. I had directional lighting on the factory set address of 03, but the loco would not move in either direction. When the address was switched to 00 for a DC loco, it would move in both directions, but there was no directional lighting.... all while still buzzing like DC. After about 3 seconds, the decoder fried and started to smoke. How can I have lighting on on one address and motion on another? Is it possible the decoder was faulty directly from the factory? I did not attempt to program the decoder, I was just performing a test on the factory settings. Any advise here would be very much appreciated. Thank you.

Tags: DCC , trouble
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Posted by tstage on Tuesday, July 10, 2018 10:54 PM

Irish,

Sounds like you may have shorted a wire to the chassis.  Does the Digitrax decoder come insulated in heat shrink?

I'm guessing you also programmed it on the main vs on a programming track?

Tom

http://www.newyorkcentralmodeling.com

Time...It marches on...without ever turning around to see if anyone is even keeping in step.

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Posted by irishRR on Wednesday, July 11, 2018 12:03 AM

This is a drop in decoder with metal pick ups that contact the motor pick ups on both sides of the chassis. There are no wires on the decoder or on the chassis to the motor. I made no attempt at programming, I was simply testing the loco on an isolated programming track (with no other locos) at the factory default address of 03 after I dropped in the new decoder. the decoder was not insulated in heat shrink. I am just wondering why the decoder was functioning on 2 different addresses... 03 for the directional lighting and 00 for the power to the engine. All while buzzing as if it had a DC decoder and not a DCC. Has anyone had faulty decoders brand new out of the packaging? This is very unusual to me. 

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Posted by richg1998 on Wednesday, July 11, 2018 1:27 AM

"This is a drop in decoder with metal pick ups that contact the motor pick ups on both sides of the chassis".

That seems to be the problem if you did not isolate the motor. Buzzing means DCC, AC portion is getting to the motor.

I use to run a DC loco on stretch zero bit with an old DCC system that could do it and the loco motor would buzz.

 

Rich

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Posted by rrinker on Wednesday, July 11, 2018 6:50 AM

 What loco and what decoder? Is this N scale? Usually there is kaptopn tape needed to insulate the motor tabs from the track pickups when the decoder is installed - on DC the two tend to wrap up on to the light board on top of one another and they are supposed to touch, but with DCC that's a no-no. 

 Very definitely what happened here, the motor wires were touching the chassis. That explains the symptoms and the result. That it didn't fry instantly is just a testament to the robustness of the output circuitry on the decoder, usually a condition like this is instantly fatal to the decoder. 

 The buzz is the big clue - a loco with a decoder installed should NEVER buzz just sitting there - even the cheapest old decoders didn't buzz at speed 0. Time to IMMEDIATELY remove the loco and inspect for wiring problems.

                                      --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 irishRR on Wednesday, July 11, 2018 11:41 AM

after further inspection, it appears the pick ups on the decoder were in contact with both the pick ups from the motor AND were in contact with chassis as well. Would that couse the decoder to short? I will pick up another decoder and make sure the pick ups are in contact only with the motor pick ups only and that there is no contact with the chassis. It may take a little bending of the decoder pick ups, or perhaps some insulation tape on the chassis to prevent contact to the decoder. Does this seem like it could resolve the issue? Again, any input is appreciated and I appreciate your assistance. 

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Posted by rrinker on Wednesday, July 11, 2018 1:43 PM

 The output circuit of the decoder is not designed to handle track power, so yes, this damages the decoder - usually quickly.

 What loco and what decoder? We cna help better with this information. Making absolutely sure the motor tabs do not touch the track pickups in any way would indeed solve the issue.

                                    --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 richg1998 on Wednesday, July 11, 2018 1:53 PM

irishRR

after further inspection, it appears the pick ups on the decoder were in contact with both the pick ups from the motor AND were in contact with chassis as well. Would that couse the decoder to short? I will pick up another decoder and make sure the pick ups are in contact only with the motor pick ups only and that there is no contact with the chassis. It may take a little bending of the decoder pick ups, or perhaps some insulation tape on the chassis to prevent contact to the decoder. Does this seem like it could resolve the issue? Again, any input is appreciated and I appreciate your assistance. 

 

No idea the scale or model of the loco.

Kapton tape is tough and thin. It can be punctured. Happened to me in a HO motor install. A ridge where I tapped for a screw puntured the tape. Had to file it smooth. I used an ohm meter to verify no connection.

Do not use electrical tape. Messy.

Rich

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Posted by irishRR on Wednesday, July 11, 2018 2:24 PM

This is N scale. I am using a Digitrax DN163K2 drop in decoder into a Life-Like RS2. This is about as easy of an install as there can be, which is why I am frustrated. It is just slide the old DC decoder out and Slide the new DCC decoder in. Pretty sure if I can prevent the decoder pick ups from contacting the chassis by using some Kapton Tape and just making contact with the motor pick ups, it should work. 

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Posted by rrinker on Wednesday, July 11, 2018 4:54 PM

 The Digitrax instruction sheet for the DN163K2 says and shows to apply Kaptop tape at the frame edges where the motor contacts go. As do the instructiosn for the similar TC K2D4:

http://tcsdcc.com/installation/n-scale/life-rs2/k2d4

This is exactly what fried your decoder, if you didn;t use tape. The stock board contacts the frame and the sides of the motor with those big clips. For the decoder install, that frame contact has to be eliminated. Regular electrical tape is too thick, not to mention messy. It may prevent the motor end of the clips from contacting. Kapton tape is much thinner (and much more resistent to wearing through from any vibration). Apply tape as shown and you shouldn't have any problem with it.

                                        --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 mfm37 on Thursday, July 12, 2018 5:38 AM

http://www.digitrax.com/support/returns/

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Posted by tstage on Thursday, July 12, 2018 7:17 AM

And a short it was.  Yea, Kapton tape is great stuff and a must-have for DCC installs.  It's also good for securing both decoder and wires to the chassis, as well as insulating surfaces on the chassis from the decoder.  Worth every penny...

Tom

http://www.newyorkcentralmodeling.com

Time...It marches on...without ever turning around to see if anyone is even keeping in step.

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Posted by irishRR on Thursday, July 12, 2018 12:24 PM

Thank you for all of your insight. This one was totally on me. I was looking at the instructions for installing into a Kato RS-2 (which does not need frame modifications) and not the Life Like RS-2 (that does need the modification). I will pick up a new decoder on Monday and I will give you all a follow up tolet you know the end result. A lesson learned..... 

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Posted by tstage on Thursday, July 12, 2018 1:40 PM

It's not always fun making mistakes but they do prove - the majority of the time - to be our best teachers.  A least it's a relatively inexpensive lesson, irish.

FWIW, I would look at the TCS decoders.  Even a road switcher looks good running slowly and TCS decoders have great motor-control.  Combine that with the Roco motors in the Kato locomotives and you've got a great combination.

Tom

http://www.newyorkcentralmodeling.com

Time...It marches on...without ever turning around to see if anyone is even keeping in step.

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Posted by irishRR on Tuesday, July 17, 2018 1:05 AM

Just want to follow up on the previous thread. I have now successfully installed the decoder into the RS-2 and it runs perfectly! Thank you to everyone for all of your insight and knowledge. I appreciate it very much. Cheers!Bow

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