# DCC Loco short circuit repair advice



## cnestor

I have a 2 years old Bachmann GE 70 DCC loco that used to work and that now causes a short cirtcuit on the E-Z Controller. I removed the shell and all the connections are like new.
It does not run either on a DC controller. Other train works fine.
What are my options? 
Is there a way to reset the decoder?
Should I send it back to Bachmann and pay the $35 fees to get it repaired?

Thanks for any advice.


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## CTValleyRR

If all your other locos work, then everything isn't "like new", no matter what your first look might suggest. See if there isn't a piece of something up in the trucks that is shorting across the power pickups.


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## DonR

A DCC loco shorting likely has a loose wire or
wiper in the trucks that is somehow touching
something it shouldn't. Unless you had a major
voltage surge to the track I'm doubting there
is something wrong with your decoder tho
that can't be ruled out.

I have two of these Bachmann DCC switchers.
The red wire came loose in the truck of one.
It did not short but I lost power from that truck.
However, if that red wire touched a wheel on
the 'other' rail there would be a short since the
red wires are tied together at the input to the
decoder. So are the black wires.

Do some tests.

Take the shell off your 70 tonner. If it has the
type of decoder that uses the little tabs to hold
on the wires from the trucks, remove them and
disconnect the red and black wires from the
decoder. (put the tabs in a safe place, you'll
need them later).

Then try the loco on the track. If you still get
a short, Make certain the two red wires are
separated, and also the two black wires. Try
again. 

If you still see a short: There is a problem in
one or both trucks. 

Use your multimeter set on OHMs. One probe
on right front wheel of front truck, other probe
on left front wheel. If you get a reading there
is a short in that truck. Inspect it closely to
determine what is causing it. There are metal
wipers against the rear of each wheel on both
trucks, a red wire to those on the right side,
and a black wire to the left side wipers.

If you get no reading on the front truck try the
rear truck the same way. If still no reading,
there is a likely a short on the decoder board
or one of the red and black wires may be
touching something.

One other thought: Have you taken the wheels
off prior to discovering the short? If so you may
have installed one or more wheel sets backward.
That would cause a short. Look closely at the
wheels. The insulated wheels should be on
the same side in both trucks. 

Let us know what you find.

Don


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## cnestor

Thanks for the answers. 
I validated that there was not a short circuit in the trucks. It looks like that the dcc board is fried .

Could I just buy a new decoder and replace the existing one. 
There is the NCE524-139bach-dsl that I could get but I am wonder if the size of the board would fit in the short size Bbachmann GE70 loco, or should I just go with a digitrax DZ123?
Do any of these decoders require some special setup after installation since I don't have anything to program them.

Thanks!

Cyril


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## DonR

Cyril

Are you certain that the Red and black wires
are not in any way contacting each other
in the area of the decoder?

You can also do another test; disconnect 
red AND the black wires from the decoder.
Then use a pair of wires from the track 
directly to the input to the decoder. If
you get a dead short then the decoder
is fried. If not then the loco should run
on the bench when you use the controller.
That would indicate there is a short in
the Red and Black wires from the trucks.

If space is a problem you can remove the
Bachmann decoder and wire in an NCE or
Digitrax. I know that Digitrax has a small
decoder intended for N scale locos that
may fit easily.

Usually, there is no need to reprogram
a new DCC decoder. You should, however,
change it's address from the default 3 to
whatever works for you. All DCC controllers
can do that easily. Check your manual.

Don


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## cnestor

Thanks Don for the info.

I took the dcc out and tested the engine only and it worked. So I decided to buy a Digitrax DZ123 decoder on ebay to play with it since it's half the price of a dcc bachmann replacement.
I wired it in place of the old decoder and the train is now working on track 3.

The only issue that I have right now is that I cannot control the light. The lights are off ( I tripled checked the wiring). I think it's due to the fact that I am using an EZ commander and the light function is not F10 per default and might need to be reprogrammed or else? 

Anybody can shade some light on that one ?

Thanks

Cyril


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## mopac

Go through all your F buttons. The lights might just be turned off.


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## cnestor

I should have mentioned that none of the F1-f10 button works.
Thanks.


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## DonR

I don't understand; the 1-10 buttons select your
locos. How do you run them if these don't work?

F10 with the yellow button is the light on/off on the
Bachmann controller. Works fine in 2 of my locos
with Digitrax decoders.

Sometimes a decoder goes awry. You can often
restore them by changing the address back and
forth ending a 03. If the decoder then controls the
lights you can and should change the address to something
other than 03.

The blue wire COMMON for lights is POSITIVE on the decoder. If you have LEDs you may have them wired backwards. It
provides 12 DC, so you may need a current limiting
resistor, 470 to 1,000 ohms.

Don


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## mopac

I think he meant F1 through F10 did not work the lights.


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## DonR

The Bachmann DCC controller doesn't have
F1-10. It has only 10 buttons to select a 
loco. To turn the lights on and off of a specific
loco you press it's address button, the the yellow
button, button 10 and the yellow again.

http://www.activepowersports.com/ba...transformer/?gclid=CNjvr4f5yM8CFZOHaQodoegEIQ

Don


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## cnestor

My controller has a Function button (Fn), that's what I meant .

Anyway I tried what Don suggested and changed the address for the loco to track 1. I now have the front light working. The back is off, I will have to double check the wiring or just put a new led.

Per curiosity, why is the Bachmann board 4" long with lots of components and does the same thing as the Digitrax dcc whici is the size of a penny?

Thank you all for your help.

Cyril


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## DonR

Cyril

Bachmann apparently figures that manufacturing
will be simplified by using a printed circuit board
decoder as apposed to the obviously more
compact design of Digitrax. It also combines
the light board with the decoder.

The loco lights are directional, headlight on
forward, rear light on backing, never both
at the same time.

Are you saying that the headlight comes on when
you go forward but the rear light does not
come on when the loco backs? 

If so, check the rear LED for a secure electrical
connection. 

Don


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