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Problem with Bachmann 158 DMU


Mike Friedman

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I have a Bachmann 00 158 2 car DMU that has been working OK for several years with a Lenz Gold decoder. When I tried to run it today (on DCC) it would not move and the lights were not working. I thought it might have lost it's address so tried to re-programme it with Decoder Pro yet kept getting the message locomotive not found.

 

Yet when I tested the dmu with dc power (the decoder still in place) it works, as do the lights, changing from yellow to red if the polarity is reversed.

 

I removed the decoder and re-programmed it using my sprog, Decoder Pro and my Loys toys decoder tester and it was recognized and decoder pro reported all the programming was OK.

 

Yet when replaced in the dmu it does not respond to DCC and Decoder Pro gives the error message locomotive not present, yet when tested with DC power to any of the four axles it runs and the lights work correctly.

 

I am stumped! The decoder is clearly OK as tested by the decoder tester, the wiring to the motor and lights is OK (or it would not work on DC with the decoder plugged in) yet it will not respond to the DCC signal, I am using the correct DCC address, so what could be wrong?

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Given you have a Sprog, I would try to read the decoder inside the DMU with the sprog. If nothing, then it suggests a wiring fault in the DMU.

If it reads inside the DMU, then try running with the Sprog (using the JMRI software throttle, remember to turn on track power with the software power control).

 

If it runs on the Sprog, then the problem appears to be a setting in your DCC system. Try the loco on a different address, or try a system reset of your DCC system (process for this differs between every maker).

 

 

It is possible to have a wiring fault which permits DC running, but stops DCC running - a wire bridging from track to motor would achieve this. But a fault which appears in a previously reliable loco ought to have a cause.

 

 

- Nigel

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Thanks Nigel, the problem obviously first appeared when I tried to run the DMU on the layout in the attic, I then tried re-programming the address on the programming track in the attic using my Lenz LZV, serial interface and the laptop that runs RR&co using decoder pro, it reported the fault :â€locomotive not foundâ€.

 

I then tested it in my office using my yard of test track, decoder pro and the sprog and it reported the same fault: “locomotive not foundâ€.

 

I have been testing it on the yard of track with the JMRI throttle (I know this is working as I tested another loco on it and it works) also the decoder tester clips to the same yard of rail and using the JMRI throttle I can see the relevant LEDs lighting up on the decoder tester when the commands on the screen throttle are activated (hence I also know the decoder is working properly).

 

You mention the loco could work on DC but not on DCC, is this possible with the decoder in place?

The power pick-up wires, motor and lights are hard wired to a 9 pin JST socket that the decoder plugs into, I though, possibly wrongly, that the running on DC but not DCC fault was not possible if the decoder was in the circuit when testing on DC.

 

The DC testing was done from an old Clipper I use when wheel cleaning, with power directly to the wheels with the decoder still plugged into the JST socket.

 

It must, as you say, be a wiring fault that has developed in the loco, possibly in the JST harness. It looks as if I will have to re-wire a new JST socket and see if it eliminates the problem.

 

Thanks all for your help, when I get a free minute I'll get the soldering iron out, do some wiring and report back.

 

Thanks smokebox, the rails and wheels are clean, this as you mention is important as the “locomotive not found error†can be caused by dirt on either.

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You mention the loco could work on DC but not on DCC, is this possible with the decoder in place?

The power pick-up wires, motor and lights are hard wired to a 9 pin JST socket that the decoder plugs into, I though, possibly wrongly, that the running on DC but not DCC fault was not possible if the decoder was in the circuit when testing on DC.

 

 

Yes, its possible, though I find it surprising in a loco which previously worked correctly(*). Before you get the soldering iron out, some tests with a multimeter on the socket in the loco might help. Look for continuity between one of the pickup wires (black/red) and one of the motor wires (orange/grey) with the decoder removed from the JST socket - its necessary to test all combinations to see if there is a path inside the DMU.

 

You said the decoder works correctly in a decoder tester. Does this have a real motor in the tester, or just some very low current LEDs to indicate motor activity ? It may be worth checking the decoder with a real motor to be sure it does work correctly; either on the bench or in another model if possible.

 

 

(* I've seen it happen when motor tags connecting internal circuit boards bridge to chassis elements, but I'm not familiar with the internals of the DMU you own, so don't know if this is possible ).

 

 

- Nigel

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Well it turned out Smokebox was on the money and I feel somewhat foolish, I checked all the wiring within the 158 and could not find a fault, and when DC running was turned off in the decoder it correctly would not run on DC, so in desperation I cleaned the wheels (these did look clean to the eye) including the backs of them where the pick-up wipers act and lo and behold decoderpro was able to recognize the loco and it ran as intended on the test track and on the main layout.

 

What had foxed me was that it would run on DC, but this was because the power was applied using my hand made plywood handle with two phosphor bronze strips that I use to power the locos when cleaning in a cradle and the contacts are made more on the top of the flanges rather than the tread.

 

The 158 must have escaped the cleaning roster on the last cleaning session; my excuse and I'm sticking to it :scratchhead: .

 

Anyway thanks to Brian and Smokebox all is well again and no expensive repairs required.

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