Bachmann K4 expert needed

[randgust]

OK, so Bachmann is pretty good on documentation but not good enough. 

I'm trying to diagnose what 'may be' a decoder issue or no issue at all.  Everything works but the motor, on DC or DCC.  The pin-outs on the 9-pin are clearly labelled motor + and motor -, but they aren't apparently labelled on the 6-pin connector between the loco and the tender on any documentation I can locate.   

I just want to disconnect the tender and hot-wire into the locomotive without necessarily having to tear everything apart  into the frame to figure which pair of black wires is the motor pair.

Anybody know?   Yeah, I can tear it apart, but I'm just trying to see if the motor even responds to a DC supply before I got that far

[Lemosteam]

The motor has a red and blue wire that the black wires connect to sometimes you can see them.  The boiler comes off very easily, just dont lose the screw bushings,  Here I have documented how to pull the loco apart:

https://goo.gl/photos/aEg2VCPhHzvPBP6F8

Some of the pics might show them.  Also the connector cannot be reversed so the motor markings on the OEM board will match to the ones on the connector.

[randgust]

Well, that was successful in that I was able to hotwire into the chassis with DC and discover that the motor and connections are good all the way back to the 9-pin connector. She runs OK on dc with the decoder board removed.

Now, I can toggle the headlight on and off with DCC, and the air compressor sound come on, so the decoder is not dead.... but no response on the motor, and I've checked with other units OK.  Being a DCC luddite, is it more likely that the Bachmann decoder is trash, or needs a full factory reset?

This may have to get moved over to the DCC world, that's OK.

[greenwizard88]

The Bachmann decoder is a soundtraxx decoder, they're pretty hardy in my experience - as in they're the only brand decoder I have yet to fry.

My first thought would be to reset your decoder, because why not, right? And then if you can, reset your command station too. Again, because why not.

After that, if you take a multi-meter to the motor wires, do you get anything? Because I'd be willing to bet that it's a fried decoder over a blown motor. But it's also possible that the siderods are out of quarter and completely binded (bound?). I had that problem with my K4, but only while running forwards, reverse was (uselessly) fine.

[peteski]

The Bachmann decoder is a soundtraxx decoder, they're pretty hardy in my experience - as in they're the only brand decoder I have yet to fry.

My first thought would be to reset your decoder, because why not, right? And then if you can, reset your command station too. Again, because why not.

After that, if you take a multi-meter to the motor wires, do you get anything? Because I'd be willing to bet that it's a fried decoder over a blown motor. But it's also possible that the siderods are out of quarter and completely binded (bound?). I had that problem with my K4, but only while running forwards, reverse was (uselessly) fine.

I think that what was mentioned in the post above yours pretty much eliminates the motor and mechanism as the problem.

. . . I was able to hotwire into the chassis with DC and discover that the motor and connections are good all the way back to the 9-pin connector. She runs OK on dc with the decoder board removed.

Yes, decoder seems like the likely problem.  I agree that a decoder reset would be the first thing to try (especially since the decoder makes sounds which indicate that at least some circuitry is working).

[Maletrain]

since you said you are a "DCC luddite" , I'll ask if you are sure that your decoder has not been assigned a consist number.  Do you have a way to check CV19 to be sure that it is zero?  If it has a number in it, instead of being zero, it would allow you to use the decoder to turn on lights and sounds, but not run the motor.  But, sending direction and speed commands to the consist address would allow the motor to run as expected.

[randgust]

Well, I've successfully hotwired it into DC, done all the mechanism work I can do (and it runs great) so I'm closing it up and getting it back to the owner, who can debug the DCC issues as much as he wants.
Mark (Spookshow)'s tip on cross-wiring the 9-pin connector certainly worked.   I'd thought the front 6-pin connector was the fault (broken wire somewhere) but it wasn't.

I was really surprised on how much lateral play there is on the drivers, I can see how you'd want that on the center one, but the #1 and #3 axles have so much that the locomotive is 'almost' free to crab down the track if the tender drawbar wasn't holding it back.  That creates a lot more side angle on the lead truck, too, for curve clearance.

A tip I discovered, completely by accident, is that you can lift out the #3 driver easily (it's not rod connected) which effectively free-wheels the two driver sets that remain, along with rods, pistons, etc. so you can finger-roll them looking for running gear problems - which I found and corrected.  But you don't necessarily have to pull the entire motor/worm out to do this.