Dead loco or bad decoder?

Model Railroader Electronics and DCC
1

Please go ahead and roll your eyes now, just to get it out of the way. [:D]

I remembered today that I have a Spectrum 4-8-2 mountain that I bought years ago on ebay. One of the reasons I had forgotten about it is I never had any way to test it - no power pack, etc. When I finally got a powerpack last fall, I tried to run it, but the model wouldn’t move. I packed it up in the box, and there it sat until today.

So being much more wiser in these things than I used to. I took apart the tender, and lo and behold, there was a digitrax DH 121 decoder plugged into the board. I took it over to the programming track, set a new address, and stuck it on the layout.

It moved down the track about 15 inches, and stopped after it passed a feeder wire. I pushed it back, and it reversed back down the line, until it passed a different feeder, it just stopped dead.

I figured the decoder might be bad, so I swapped out the digitrax with a bachmann one that came from a consolidtion. Nothing, wouldn’t move, wouldn’t let me programm the address

I removed a tender from a 2-10-0 that I have (also spectrum) that runs well, and attached it to the mountain. Nothing. Wouldn’t move or respond.

I put the digitrax back in, and still nothing. Reprogramming the address failed, failed, failed, took. MY CVP controller was giving me wierd messages; told me it was not a 3 type decoder when i went to reset the defaults on CV8, than took it.

So what do you think I’m looking at here.

A bad loco?

A bad decoder?

Both?

I’m kinda leading towards a bad loco, as the spectrum decoder I put in was working fine on the consolidation before I replaced it. With the 2-10-0 tender, can you just swap these out like that? I figued it should work, as the wiring should be the same on each.

Thanks in Advance.

2

Sounds like the loco can use a good cleaning. If it still doesn’t do well remove the decoder and put the Digitrax one back in. If it still doesn’t do well you’ll have your answer.

3

The tender for a 2-10-0 isn’t compatible for use with a Mountain. The circuitry is different. The tender for a light Mountain and the Consolidation are the same so they are interchangable.

I agree with Jeff that a good cleaning is in order and a light lubrication if it has been sitting for a long time, then try it with your Consolidation tender assuming it is a light Mountain. If it is the heavy Mountain the tender for the consolidation won’t work as the heavy has, you guessed it, different circuitry in its tender.

I suggest you do a search on the Bachmann forum for tender compatibility between the various Spectrum locos. You would think that they would be the same but they aren’t. I wanted at one time to get a Hicken Vanderbilt tender for my light Mountain but it would involve switching the circuit board between the tenders as they aren’t compatible.

4

Thanks - to you and Jeff for your advise. I’ve never cleaned a locomotive before, so I’ll do some research on how to.

I didn’t use the consolidation tender becuase the wires are reversed - the plugs come from the loco on the 2-8-0s, and from the tender on the 2-10-0 and the 4-8-2.

I’m oddly not upset this isn’t working. I’m unlikely to take apart a nice working model, but as I may have to hack into this one, I may as well do some some other mods while I’m under the hood, such as detailing, a new Tsunami decoder, etc. But let me see if I can get it running first.

Cheers!

5

Does you system show you a dead short, or does the loco just not respond?

Will the decoder respond if you just have the tender on (CV read back)?

I am trying to narrow down where the issue lies…

How do the wires look that come from the tender or the locomotive? Any fatigue or such in the wires? How do the male and female ends of the plugs look? Does it need replacing?

Open up the tender. Do you see any signs of a short or arcing? How do the soldering points look? Is the big orange capacitor still on the board (it should have been cut).

Can you confirm decoder operation by plugging it into another loco?

David B

6

Thanks. it was bad wiring. I had some time this evening, so I took the tender apart, and started messing about. I finally got it running (it would do almost a lap on my layout before dying in the same spot everytime…) by installing the Bachmann spare decoder, and unscrewing the circuit board. Once that was unscrewed, the model ran fine, althoiugh I could stop it by jiggeling the circuit board. It’s a short.

I’m mostly suspicious the problem is with the orange and red wires that are soldered to the bottom of the circuit board, as they may have been pinched by the screw that holds the board down.

I’m going to put it on the bench, and check everything securely. I appreciate your help, the questions you asked helped me think about how to troubleshoot this.[tup]

Cheers!

7

If it’s not tripping your system’s circuit breaker when it stops, then it’s probably not a short but rather an open. In other words, a loose connection, a cold solder joint, or as you observed a pinched wire that has broken inside the insulation.

8

Thanks for the clarification. Here’s the board

I think it is the two wires that show here on the upper right of the underside of the circuit board.

Actually, with the board like this, it runs flawlessly.

9

Scarpia

Rip the board out and wire the decoder in place. Dont forget a 1K resistor for the headlight.

The Bachmann boards are junk and have too many unnessesary components for DCC running. Caps and Chokes are put on the board for noise filtering and will play with a decoders settings.

Pete

10

No need to rip it out. Just make sure the solder joints where the red and black wire go in are tight the cover the solder side of the board with electrical tape.

11

So you’re saying the circuit board is nothing more than a interface? This model also has a firebox door effect - does that need to be resistored as well?

I’m a bit nervous at the prospect of pulling the board, now that it’s working.

Jeff’s idea of tape isolation might be the path to go.

Thanks!

12

I have a couple Spectrum DCC locos. The PC boards are an interface. All you need to do is snip the capacitors. I and others have done this. This is a known issue for the Bachmann Spectrum line. Without the two capacitors, the two small inductors are not an issue, though I have removed them and soldered in a piece of small diameter wire so I had a little more clearance. The caps and inductors form a filter network. Both are needed together to do the filtering. The UK, EU require the inductors and caps for supposed interference issues. Do a Google search for spectrum dcc capacitors. You will see. Tony’s trains and other DCC vendors say the same thing.

The resistors for the lamps are on the PC board. Like you were told, use 1k resistors for LEDs if you remove the PC board. I use Kapton tape for insulating. I get the tape from Litchfield Station. This tape is thin and tough.

Here is a good link for a lot of DCC info.

http://www.members.optusnet.com.au/nswmn/index.htm This guy is in some of the Yahoo DCC groups.

Rich

13

Thanks for the input. It looks like that this problem was rectified on post 2005 models from Bachmann, at least from what a couple of the threads that are out there. I dont’ know when I got this Mountain though, I really cannot remember.

My other bachmann dcc equipped steamers run great though (even better with a plug and play Tsunami).

I think I’ll pull the circuit board anyway, as practice for myself. So I need a 1k resistor for the head lamp, what about the firebox light?

I presume that If I add a back up light to the tender, I’ll need another 1k resistor for that?

Thanks