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Need help diagnosing a short circuit

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  • Member since
    March 2014
  • 82 posts
Need help diagnosing a short circuit
Posted by tony22 on Friday, February 27, 2009 6:37 PM

I installed a TCS CN in one of my Atlas RS-1s and when I put it on the programming track my NCE PowerCab indicated a Short Detected. While on the P-Track there was a buzzing sound and the rear headlight was on. So I cut the power to the track and pulled out my multimeter. There is no short between the frame halves. The trucks are in the correct orientation. But there is continuity between the gray and orange wires and one side of the frame (but not the other).

This seems to suggest that both of those paths are shorted to the same side somehow, but I checked both of those connections to their respective motor bosses and can find nothing obvious. I have Kapton tape around that part of the motor housing to isolate the motor from the frame.

I've done a couple of other CN installations and they've been fine.

  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 23,330 posts
Posted by selector on Friday, February 27, 2009 8:11 PM

Have you inverted the engine with the shell off and given it a blow or a gentle shake?  Sometimes we inadvertently leave a small clipping of wire-end bridging two electrical paths, or there is a tiny filament of wire touching another wire nearby of opposite polarity.  Is there a light board involved?  No axles were inadvertently swapped end-for-end?  You haven't forgotten a piece of metal, a metal implement, lying across the rails someplace?  Over time and the effects of gravity, some bared wiring hasn't migrated over to make contact with other wiring under the bench?  You don't have a power routing turnout misaligned?

I'm just guessing, of course.  If other engines do fine, then you would know it is within the engine in question.  But it suggests, then, that you have miswired, or misread something.

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Posted by tony22 on Friday, February 27, 2009 9:36 PM

It turned out to be the upper motor boss having poked through the one layer of Kapton I had wrapped around the motor housing. I left a bit of a solder blob on that one. So I wrapped a bit more Kapton around the motor housing and put it all back together. Unfortunately I got past one problem and found another. Now the Programming Track allows me to do all that I should - set the configuration, program the loco number, even do a reset. When I go to the main track I can increase the throttle, hear a sort of pulsed buzzing, but I get no motion from the engine.

I hand rotated the flywheels. There doesn't appear to be any binding (I was worried the extra wrap of tape would maybe be causing some weird kind of pressure). Headlights work in both directions. Just no motion. Even with the throttle all the way up.

I did notice this time that when I acknowledged the manufacturer and version numbers that this engine didn't "jump" as much (y'know, when you do each step the engine moves forward a bit to indicate it received it).

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Posted by mfm37 on Friday, February 27, 2009 9:37 PM

There should be some resistance between the grey and orange wire. They are connected to the motor.

There should be no continuity between the grey and orange wires and the frame halves. If there is, look for a short. RS1 is a tight installation for any decoder.

Since the rear head ligt is on, start at that end. Could be a solder bridge or a hair on one of the soldered connections. Pay particular attention to the blue wire where it was soldered between the front and rear boards.

Martin Myers

  • Member since
    October 2004
  • From: Colorful Colorado
  • 8,639 posts
Posted by Texas Zepher on Friday, February 27, 2009 10:49 PM

tony22
It turned out to be the upper motor boss having poked through the one layer of Kapton I had wrapped around the motor housing. .... When I go to the main track I can increase the throttle, hear a sort of pulsed buzzing, but I get no motion from the engine.

The first problem might be cause of the second problem.  Since there was continuity between the grey/orange wire and one side of the frame, as was indicated in your first post, the portions of the motor output section of the decoder is probably burnt out.   The decoders cannot handle power coming in "backwards".

Put a DC voltage meter between the orange and grey wires and see what it says when the throttle is advanced.  I'm guessing the hum is caused by raw DCC getting all the way through the decoder into the motor.

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Posted by tony22 on Saturday, February 28, 2009 5:36 AM

Texas Zepher

The first problem might be cause of the second problem.  Since there was continuity between the grey/orange wire and one side of the frame, as was indicated in your first post, the portions of the motor output section of the decoder is probably burnt out.   The decoders cannot handle power coming in "backwards".

Put a DC voltage meter between the orange and grey wires and see what it says when the throttle is advanced.  I'm guessing the hum is caused by raw DCC getting all the way through the decoder into the motor.

But TZ, even while I'm on a Programming Track? I did not place the engine on the main track until after fixing the Kapton problem. But I'll check it.

When I use the meter, what should I see if it's working vs. not working?

  • Member since
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  • 82 posts
Posted by tony22 on Saturday, February 28, 2009 7:13 AM

mfm37

There should be some resistance between the grey and orange wire. They are connected to the motor.

Martin, near as I can tell at the moment it is open between the grey and orange wires.

I had a bit of trouble with the motor bushing tab where the solder blob wound up appearing. It's possible I may have had the soldering iron on the tab for a bit too long (~10-15 seconds, but it took that long to get the solder to flow). If that's the case is it possible I blew something in the motor assembly?

I know I'll have to pull the decoder wires off and check the motor, but I won't be able to do that until tomorrow.

  • Member since
    December 2002
  • From: Mo.
  • 227 posts
Posted by armchair on Saturday, February 28, 2009 8:29 AM

 Tony, Texas Zeph. may be right. You're loco shows the same symptons as My atlas s2 .I smoked that nce dec. ! it don't take much either ! I did learn a lesson, to be more careful when installing decoders though. R.......

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Posted by mfm37 on Saturday, February 28, 2009 11:26 AM

tony22

I know I'll have to pull the decoder wires off and check the motor, but I won't be able to do that until tomorrow.

 

 

Not Really., but you will need to reduce the size of that solder blob.  See my reply on the Atlas forum.

Martin Myers

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