# Oddly dead decoder...



## riderdan (Jan 2, 2014)

Last week, we had company over from out of town. While prepping for visitors, I was working in the garden and thought I'd run a train around the layout. What was handy was my Mac switcher, which had a Digitrax DG583AR installed. I'd picked the decoder up for a song--I guess the seller thought there wouldn't be much call for Aristo decoders when they went under. Since the Hartland Mac obviously doesn't have an AR plug, I soldered the pins to wires from the motor, track pickups, and lights. It's run fine since.

Anyway, I let the switcher run around the track while I was working, went in and had dinner, then came back out for an hour or so. Near the end of that time, after about four hours of running, the Mac stopped. Occasionally this is caused by running over bug (in the fall it's usually crickets, of which we have an abundance this year) so I went over to check it out. Nothing seemed wrong, no dead bugs on the track/wheels, but the loco wouldn't go. I brought it inside to my workbench and fired up JMRI and my SPROG and got no response, either when sending commands or when trying to read CVs. In fact, the SPROG was reporting a short circuit.

I opened the loco up and immediately saw that one of the track pickup wires was somewhat melted. This was a 18ga wire that ran from the added track skates to join the wire from the wheel pickups before they were connected to the decoder. I didn't see an actual short in the wiring and don't suspect one, because the wire ran along the plastic motor block and up through the body shell to the decoder, and wasn't routed with the opposite pick-ups wire. It also doesn't touch anything metal. Possibly the wire was of insufficient gauge for the load when the pickup was the only path for the current.

With the loco shell off, I tried a direct connection to the decoder. I have a set of alligator clips that provide a secondary connection to the SPROG which I connected to the decoder's track input pins. When I turned the SPROG power on again, it again reported a short circuit. 

To narrow things down, I decided to pull the decoder out and see what I could see. I pulled all the wires off the decoder and hooked it up directly to the SPROG. Again, I connected the alligator clips to the decoder track inputs. The motor pins I connected to a loose LGB motor I have to provide a load. Short circuit again. 

It appears that the decoder is fried, but I'm not sure how that could have happened. It doesn't seem like the melted pickup wire, which is isolated from all the other wiring, could have done it. Anyone have any thoughts? I don't want to have the same problem again when I put a new decoder in.


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## Cougar Rock Rail (Jan 2, 2008)

I would be suspicious of the motor. I think what may have happened is that the motor started drawing too much current, which melted the power pickup wire and eventually overheated/overloade and nuked the decoder. I guess the Digitrax decoder doesn't have good self-protection and didn't shut itself down.
You may want to check the power pickup on all of the wheels, too, because maybe all the current pickup is being done by the skates which might also explain the melted wire. Try connecting DC power to the motor and see if it runs OK, try putting a little load on it etc., see what happens and how it react. My bet is that the motor is worn out, though.

Keith


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## ewarhol (Mar 3, 2014)

I agree with Keith on the decoder getting nuked. Contact Digitrax customer support. I've had excellent care with them in the past. Sent decoder in for repair and received a new one back.


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## riderdan (Jan 2, 2014)

Cougar Rock Rail said:


> I would be suspicious of the motor. I think what may have happened is that the motor started drawing too much current, which melted the power pickup wire and eventually overheated/overloade and nuked the decoder. I guess the Digitrax decoder doesn't have good self-protection and didn't shut itself down.
> You may want to check the power pickup on all of the wheels, too, because maybe all the current pickup is being done by the skates which might also explain the melted wire. Try connecting DC power to the motor and see if it runs OK, try putting a little load on it etc., see what happens and how it react. My bet is that the motor is worn out, though.
> Keith


Good point, Keith. It's a 5A decoder, but you might be right about the motor. I was pretty sure the wheel power pickups were OK, but I'll check those, too. I have my DC power supply in a box somewhere, but checking the motor is a good troubleshooting idea.


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