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someone "let the smoke out" Track and electrical/DCC
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Super User 1,071 posts Kirk W kirkifer Super User 1,071 posts
Kirk W kirkifer

I bought an almost brand new Broadway Limited SD40-2 that would not run and would short the DCC. Hey, it was like $29... So, I think that was worth the risk?  After taking the engine apart, here is the fried circut board I found. The smell is horrible...  i can't tell if it is just the circuit board that is smoked or if the motor has issues too.

I took the motor out and it turns freely by hand. When power is applied, it seems to run quiet and smoothly. There is the same burned electrical smell, but I can not see anyplace on the motor that looks melted or scorched or has any damage.

THE BIGGEST QUESTION: What do you suppose caused this damage? It looks like the plug for the motor power was melted along with the corresponding part on the circuit board. My guess initially was that someone switched their layout to the G scale setting or something, but that should have ruined other portions of the board, correct?

%20board.jpg 

Although I did not know Broadway limited sold these DC versions, I think I am kinda glad that it did not have a fried sound decoder in it, because it would probably have made me nauseated.

Does anyone have any recommendations? should I try and save the remaining plugs by desoldering them from the board? My best guess is that I will just put a TCS WOW in this thing and be up and rolling... OR should I try to get a new circuit board from BLI or what?

 
Kirk Wakefield
Avon, Indiana
 

 
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Big Zeke -On30 Active Member 77 posts
Big Zeke -On30

Wire it as a DC motor and run

Wire it as a DC motor and run it for an extended period before replacing the PC board, that is what I would do, this would check motor and mechanics of the trucks.  Zeke
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joef MRH Founder 17,575 posts
joef

Could have been a derailment

Could have been a derailment where the locomotive was in a shorted condition on the track and left to just sit that way for a minute or more. With 5 amps or more going through the electronics something has to give and often it's the loco circuit board / decoder. The other possible damage point could be the wheelsets / trucks. Check close for dark electrical arc spots on the loco trucks.

Joe Fugate​
Publisher, Model Railroad Hobbyist magazine

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Kirk W kirkifer Super User 1,071 posts
Kirk W kirkifer

run as DC

Yep. That is an excellent idea. I want to put a WOW sound in it, but I would be afraid of a dragging motor and stall current. Weird things can happen that are not caught on a QC check.

Joe, might have an excellent point. When I pull it back apart, I will check it for those spots. I did not disassemble the trucks initially. I actually lost a decoder this way due to a shorted old blue box with metal sideframe trucks.
Kirk Wakefield
Avon, Indiana
 

 
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Virginian and Lake Erie Super User 9,250 posts
Virginian and Lake Erie

I would consider the motor as

I would consider the motor as needing a replacement and use a new decoder. It is possible something inside that motor is toasted and may present a problem later. I would also look very closely for anything that could be causing a short in the drive train. I would start at the wheels and work upwards checking to make sure there is nothing conducting power that should not be doing so.

Rob in Texas

MRH Blog / Prep for an Operating Session / Delving Into the Past / The Club Blog / Youtube / etmrc.org
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Mark R. Regular poster 293 posts
Mark R.

Current Draw

The motor might not be harmed. Check the current draw on DC. If it is drawing unusually high current, then the windings are probably shot. If the current draw is still normal, you can still use it safely.

 

Mark.
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lexon Prolific poster 1,211 posts
lexon

Current draw

In case you have not done it before. Just put the amp meter in series and run at 12 vdc. lock the rotor.

Rich
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mran8 Regular poster 136 posts
mran8

It appears that the board

It appears that the board probably saved the motor!  At least that's where all the power went.  The board connectors look standard and are probably not worth messing with.
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Les Staff WEUSANDCORR Regular poster 220 posts
Les Staff WEUSANDCORR

That would of been buzzing if

That would of been buzzing if on dcc track and would have caused the burnt plug. Looks like you'll be hard wiring decoder in or you could after checking motor etc plug it back up without motor connected and put it on dc track and check light function , If ok then you could remove the dc jumpers and plug an eight pin decoder in and remove the motor wires off the plug and hard wire to motor.  At least most of it would be plug up

Les

WEUSANDCORR est 1976     The C&NW is alive in Oz  the land Down under
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dsnyder44 Active Member 34 posts
dsnyder44

Check for voodoo

Worked with a lot of electronics in the past and sometimes there is voodoo in those wires. But, I would look very carefully at the motor and everything else in the electrical path. When nothing is obvious sometimes it is a loose connection, or foreign object or as weird as shavings that move around in the system. 

The other recommendations are great: 1. Measure current draw - loaded and unloaded,

2. run it on DC for an extended period. Leave the shell off so you can feel the warmth of the motor. 

3. check everything with your magnifiers on. Amazing how many electronics problems can be solved visually. 

Personally, I wouldn't worry about the connectors. I would just hard wire it in place. 

Dennis

Dennis Snyder
Colorado Springs, CO

https://www.facebook.com/CentralRockies
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Kirk W kirkifer Super User 1,071 posts
Kirk W kirkifer

I threw the board away

Before chunking the board, I took it to a local ops. session. Someone pointed out the solder job on the back of the board, right where the burnt plug was looked chunky and not factory. I would have no way of knowing if it was a poor home mechanic job or not.

It did look a little sloppy, for sure. If that was causing a short, I guess it would have burnt that area very fast, especially putting it on a 16-20 volt AC circuit, right?

So, as Dennis pointed out, perhaps this was easier to diagnose than it seems?
Kirk Wakefield
Avon, Indiana
 

 
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Prof_Klyzlr Moderator 7,962 posts
Prof_Klyzlr

Analog Loco on DCC

Dear Kirk,

Quote:

Does a buzzing DC engine sitting on a DCC track for an extended period really burn things up? 

Short answer, Yes.

Slightly longer answer:

For a loco which is "pure analog" (motor literally wired direct to the wheel pickups),
being subjected to the AC-esque alternating voltage causes

- motor heating
(volts directly accross motor coils)

- motor heating
(collapsing magnetic field as the polarity swaps)

- commutator and brush heating/burning
(high current passing thru a single stationary point on the commutator, rather than always moving around the commutator)

- Bearing and mechanism/gearing damage
(high speed violent Back/forth rocking of the motor transmitted thru the drive)

Believe the deep details have been discussed here onlist previously...

http://model-railroad-hobbyist.com/node/25414

Hope this helps...

Happy Modelling,
Aim to Improve,
Prof Klyzlr
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