decoder or track?

[mrredrunner100]

hi, i have a london 2012 class 395 "javalin" train that i have converted to DCC, the train runs but every so often i turn the power down to off it just continues at the same speed and the power selected on the select controller has no effect on the train,

 

and when i try to start the train sometimes it crawls along at a very slow speed without speeding up to the set power.

 

no other trains on my layout do this, so would this be a track or decoder problem or something else that i have missed? and any ideas

 

on how to fix it?

 

thanks

 

mrredrunner100

[Fishmanoz]

Sounds like a faulty decoder to me mr. Easy to check - swap this decoder for another in one of your other locos and see if the other loco now has the fault.

[mrredrunner100]

Fishmanoz said:

Sounds like a faulty decoder to me mr. Easy to check - swap this decoder for another in one of your other locos and see if the other loco now has the fault.

thanks for the reply, i have a spare brand new one

that i will try in the loco in question, i will put it in in the morning when there is a bit more light

mrredrunner100

[Augustus Caesar]

Also check your wiring just in case one is loose or maybe connected wrongly... in which case two wires would be wrong.

 

The decoder could be the reason though... had one do this a couple of years back.

[mrredrunner100]

I tried replacing the decoder but it did the same thing

[Michael_A]

Have you left any capicitors or chokes in the loco itself? Just possible these are filtering out the control data sent with the DCC supply voltage.

[Fishmanoz]

You made me think on this Michael. In DC configuration, RF suppression capacitors sit across the motor connections and chokes in series with a pickup and a motor connector. They are low pass filters having little or no effect on the DC power to the motor

 

while blocking any RF hash generated.

 

If they are left adjacent to the motor after decoder installation, they sit across the decoder output to the motor and so will be isolated from the track by the decoder. Despite being unneeded as the decoder does

 

the suppression job itself, many say they have little effect if left. To me good practice is to remove them and any possibility of degradation.

 

Leaving them at the pickup input end of the decoder is another matter entirely. Here they would be directly

 

across the track and also cumulative if there is more then one loco on the track. While I would be surprised if anyone left them this way, they would certainly cause problems if anyone did.

 

Now I'm just assuming that there is isolation between decoder

 

input and motor output. Can't see it can be otherwise given the decoder must modulate the DCC to vary the mark-space ratio to control speed. Can anyone confirm this or otherwise?

[poliss]

Turn off DC running in CV29.

[mrredrunner100]

Hi thanks for all the replys, I will work through them, about there being a capacitor, would this green thing in this image be it?

 

https://docs.google.com/file/d/0B1KO1zQcxYLWdDdBZDlWVjdIWkE/edit?usp=docslist_api

 

Because if it is then that

 

might be the problem

 

Thanks

 

Mrredrunner100

[Fishmanoz]

Will check out your link later (my iPad often gets upset at links so I avoid them) but an easy way to see what they are is to go to the DCC section of this site and look at any of the decoder fitting instruction sheets. There are photos there that show

 

the suppression components.

 

But if there are any components between pickups and motor,they are for suppression and can be removed. Once a decoder is fitted, all you should have is the decoder, pickups, wires and motor connectors, nothing else.

[Fishmanoz]

mr, if you mean the large vertically mounted component on the circuit board at the bottom left end, yes that is a capacitor but do not remove it. The board is probably associated with lighting and has nothing to do with the decoder installation. As I said,

 

the components for removal are between the pickups and their wiring and the motor connectors. They will be soldered in individually and will not be mounted on circuit boards.

 

I can see the decoder next to the orange tape but not the motor and no suppression

 

components.in the view you've shown.