help with directional short on lgb 2036 20th ann trolley

This is a real ball buster. Having pulled apart the odd 3 wires motor block to convert to DCC I have converted them to 4 wire by splitting the internal bars. Something about this issue suggests to me that the bars must somehow be getting a stray link one way but for the life of me I cannot understand how.
 
Since the motor block runs fine in both directions by itself (when the green and brown pins are jumpered) the problem must be in the body. The brown and white wires from the motor block pins are track power into the circuit board. It looks like the roof can maybe be put on backwards if is like that shown in the attached LGB service pdf for the 2035. Are you sure it is on correctly? There are three contacts on the roof, two for interior lighting and one for the pantograph. What happens when you try running from the pantograph? Switch it to overhead power. Connect the transformer to the white pin side skate and the pantograph. It does not need to be on track to do this. Does it run at all? Does it still run in one direction but short in the other? Do the lights work correctly?

If the roof is on correctly but it still shorts in one direction try unplugging both headlight/taillight boards. The trolley should run. Does the short exist? If not plug in the headlight/taillight on one end and check again to isolate.

 
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Roof on correctly…contact arrangements are obvious
Still shorts with roof off, or properly placed
tried panto connection, same
 
stevedenver said:
Roof on correctly…contact arrangements are obvious
Still shorts with roof off, or properly placed
tried panto connection, same
Click to expand...
I'm out of ideas and agree with Jon - It is a real ball buster! It's too simple a vehicle to be giving this much trouble. Maybe it's possessed!
 
So going back to the beginning:
Block (alone) with the two pins connected, runs fine..

Once body is put on, we have a short, but only in one direction?

No difference, if roof on or off, or pantograph power selected..


So the fault has to be in the main body, and associated wiring.
One direction, so it has to be after a diode.

This points to a trapped wire. Whisker on a soldered(?) connection. Bulb or LED gone short-circuit..


The only other suggestion (but I think only applies to Bachmann) is if there is a metal 'skirt' around the block? Could this be moving/catching in one direction?

PhilP
 
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It's definitely something to do with the body, are you sure there's nothing catching somewhere and causing the short?
 
Agree its in the body.
since it was fine, then it wasnt and ran only one direction,
it is, imho, unlikely any physical issue /change arose re pinched wire, stray solder, etc. as there was nothing to cause a problem like those.

i will, in the nearish future, re visit the diodes.
to my mind, it has to be some component failure.

i understand that when a diode fails, especially if subjected to high voltage, it can allow current to bleed in both ‘directions’. While i cant recall, i may have run the trolley at full voltage Briefly.

what i dont understand is having replaced both diodes, using the lgb switch diodes, which are identical in outward appearance to those on the trolly board, it still happens.
im thinking now, while the directional markings are correct, per the original diodes, perhaps one is reversed….

i will solve this, but my problem (among many,lol) is i dont know how to test polarity/diode function.
think ill read a bit….
 
stevedenver said:
Agree its in the body.
since it was fine, then it wasnt and ran only one direction,
it is, imho, unlikely any physical issue /change arose re pinched wire, stray solder, etc. as there was nothing to cause a problem like those.

i will, in the nearish future, re visit the diodes.
to my mind, it has to be some component failure.

i understand that when a diode fails, especially if subjected to high voltage, it can allow current to bleed in both ‘directions’. While i cant recall, i may have run the trolley at full voltage Briefly.

what i dont understand is having replaced both diodes, using the lgb switch diodes, which are identical in outward appearance to those on the trolly board, it still happens.
im thinking now, while the directional markings are correct, per the original diodes, perhaps one is reversed….

i will solve this, but my problem (among many,lol) is i dont know how to test polarity/diode function.
think ill read a bit….
Click to expand...
A meter will test that.put the meter on resistance, the flow direction will show a number greater than 1. Swop wires round and 1 no flow will show.
 
Thanks
but wouldnt a reversed or’leaking’ diode cause a short by feeding, say, both lighting boards, since they too have diodes for the red leds?
 
Think about it for the lamps... the diodes are there to only conduct electricity in one direction.... they do not effectively change the voltage... so the power goes through the diode (which only conducts some time) and then through the lamp. In essence, in the "proper" polarity, the diode IS a short.

If the diode was shorted, it is effectively leaving the lamp always on... a short just gives the lamp power all the time.

There are other diodes in decoders, but this is not a decoder equipped loco, right?

I believe your issue is elsewhere, a blob of solder where it should not be, an errant bit of wire.

Greg
 
Another thought, roof off chassis disconnected chassis works both ways. Put on blocks with direct connection via test leads to chassis. Now more test leads connect each part of the roof connections build up one at a time test each way till short appears. This should ID which connection chassis to roof is the issue?
 
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