DCC Troubleshoot Assistance Needed

[davefoxx]

I have a Digitrax DCC system that uses a DB150 as the command station.  This afternoon, while running trains, they started acting like they were running slower and even surging slightly.  This is occurring in multiple locomotives, so I don't think it is any particular decoders.  My Atlas SD50s and two GP9s will only go about 10-20 smph now at full throttle.  It seems to have affected my Kato F40PH less, but that locomotive is surging every now and then.

What is going on?  Everything was running fine even earlier today, so there has been no change in the wiring of the layout that should be the direct cause of this. 

Thoughts?

DFF

[C855B]

Have you removed the AR1 from the circuit yet? That's your latest big change.

[eric220]

Sounds like something started drawing a significant load. I haven't heard of the AR1 doing that, but it wouldn't surprise me. Have you run any trains through the reversing loop? Does the relay throw sound and act normally? Does anything on the rest of the layout change when the relay throws?

[John]

check the voltage of the power supply, and also across the track

[peteski]

check the voltage of the power supply, and also across the track

Unless Dave has a special DCC voltmeter, it will be tough to measure the track voltage. Use AC setting on the standard multimeter.

Another way to approach this would be to measure current draw. Again, if a DCC ammeter is not available, measure the current on the power supply (DC) side. If the surges correspond to increased current draw, that might help in troubleshooting.

[davefoxx]

Unfortunately, I don't have a multimeter.  I do have a cheap Life-Like circuit tester that's nothing more than two prongs and a light bulb.  I put it across the tracks and it does seem dimmer than usual.  It was about the same intensity when applied to the used 9V battery from my DT402D throttle, so I don't think that I'm getting full voltage to the rails.

Different locomotives are all reacting the same; full throttle achieves about 20-30% speed.
I cut out the entire new loop, including the AR1: No change.
I pulled every locomotive off the tracks: No change.

So, it is not a decoder problem or the AR1.  I'm not saying that the AR1 didn't cause this though, if something has gone awry in the DB150.  Should I try a reset of the DB150?  I've never done that before.

DFF

[davefoxx]

Problem solved.  You'll never believe it.  I don't believe it, nor do I believe my luck in finding it.  I was reading up on how to do a reset of the DB150 and went to remove the RJ12 cables to disconnect Loconet from the DB150.  While I was pulling those cables out, the wire connecting to "Rail A" on the DB150 came out.  This is one of my bus wires.  Somehow, it had come loose.  I put it back in, tightened it down, and "boom!," all is well again.  Full power!  Tim "The Tool Man" Taylor would be proud.

Thanks for your time and advice, fellas.  I guess the lesson is that I really need to go by a multimeter.

DFF

[John]

I guess the lesson is that I really need to go by a multimeter.

Yup .. and even though you can't "measure" the DCC signal with them, when you put the meter in AC 20 volt scale, you should read about 8-9 volts on the meter ..

[eric220]

Dang! I was all ready with my "told you so!" on the AR1. Guess I'll have to save that for later... 

[davefoxx]

Dang! I was all ready with my "told you so!" on the AR1. Guess I'll have to save that for later... 

There's still time . . .   

[John]

Dang! I was all ready with my "told you so!" on the AR1. Guess I'll have to save that for later... 

I have 3 of them in place for several years now .. no nuclear meltdown here either

[eric220]

I have 3 of them in place for several years now .. no nuclear meltdown here either

I had a couple work flawlessly for years too. Then one of them took down my whole layout. Never again.

[Carolina Northern]

Unfortunately, I don't have a multimeter. 

Shame on you.

Harbor Freight has a working one for 5 bucks - sometimes with a coupon it's free. Not the world's greatest, but every modeler should have at least one.

[davefoxx]

Shame on you.

Harbor Freight has a working one for 5 bucks - sometimes with a coupon it's free. Not the world's greatest, but every modeler should have at least one.

Definitely shame on me.  I'll look into that!  Thanks, Kevin!

DFF

[djconway]

Trouble shooting 101 -- Start as close to the source of power as possible
Any VOM is a good investment.