Decoder

[spenc]

Don't know if in the right place but I brought a second hand farish 170 dcc fitted couldn't get it working so got in touch with seller to see what number the decoder was set too, still would not work so simple thing to do is get another decoder as I disconnected it I gave the motor a try that worked on dc.I got another decoder which is a digitrains dz126 put that on and it works perfect put the body back on tried it not working take body of working OK again checked to see if trapped wires no put body on again not working body's all plastic so not that, it is tight fit anybody got any ideas or had same problem.

Thanks Steve 

[WIMorrison]

Body shell is pressing on the decoder or wiring that you have done and breaking a contact somewhere.

[Andacami]

A photo of the placement of the decoder would be helpful. I am unfamiliar with the model, but on anything where I have seen this behaviour, it's a short with the decoder pressing against something or the model's PCB pressing against something when the body is on. It only takes a small thing to upset a decoder, less so in pure DC mode. Again, photos would help 😉

[34theletterbetweenB&D]

Does it work on DC without a decoder fitted and the body on? That's a test for whether with the body fitted supply from the track is reaching the motor.

 

But before you take the body off and remove the decoder, do you get any communication between your DCC system in programme mode and the decoder? That's a test for wher the connection failure is occuring, before the decoder or between decoder and motor.

 

9 minutes ago, spenc said:

...had same problem.

Oh yes, don't be discouraged. Something as simple as a broken core in a wire which makes with the body off and breaks with the body on is enough, many of us have been there. As a certified hooligan my response is often to remove all the wiring and solder in a hardwired decoder: quicker than trying to find the problem 'inside' where you cannot see. 

[Izzy]

If these are 6-pin decoders then it can help ensure contact in the socket by bending/putting a kink in the pins so they are a firm fit. As said it could be the body is pressing on the decoder enough to break contact with one of the pins. If it is pressing on the decoder also make sure it's not able to press it against the metal chassis or the pcb. Some tape between the decoder and the chassis/pcb etc. can be a good idea for insulation in case this is the issue. 

 

Bob

[spenc]

44 minutes ago, Andacami said:

A photo of the placement of the decoder would be helpful. I am unfamiliar with the model, but on anything where I have seen this behaviour, it's a short with the decoder pressing against something or the model's PCB pressing against something when the body is on. It only takes a small thing to upset a decoder, less so in pure DC mode. Again, photos would help 😉

Here's some photos 

[spenc]

41 minutes ago, 34theletterbetweenB&D said:

Does it work on DC without a decoder fitted and the body on? That's a test for whether with the body fitted supply from the track is reaching the motor.

 

But before you take the body off and remove the decoder, do you get any communication between your DCC system in programme mode and the decoder? That's a test for wher the connection failure is occuring, before the decoder or between decoder and motor.

 

Oh yes, don't be discouraged. Something as simple as a broken core in a wire which makes with the body off and breaks with the body on is enough, many of us have been there. As a certified hooligan my response is often to remove all the wiring and solder in a hardwired decoder: quicker than trying to find the problem 'inside' where you cannot see. 

Yes it worked fine on dc that's what checked to make it wasn't the motor.there no communication with body on only with it off.

[woodenhead]

With the body off and the unit running, have you tried pressing each soldered connection and the chip to see if that causes any failures?

 

It might help you pinpoint what's at issue

[WIMorrison]

Personally I would cut a slot in the chassis to allow the decoder to sit inside it , that way it would be clear of the body shell. I would also insulate the end of the blue, white and yellow wires properly.

 

Also Sellotape isn't a good way to hold things on 

[spenc]

42 minutes ago, Izzy said:

If these are 6-pin decoders then it can help ensure contact in the socket by bending/putting a kink in the pins so they are a firm fit. As said it could be the body is pressing on the decoder enough to break contact with one of the pins. If it is pressing on the decoder also make sure it's not able to press it against the metal chassis or the pcb. Some tape between the decoder and the chassis/pcb etc. can be a good idea for insulation in case this is the issue. 

 

Bob

It's hard wired no plug and socket decoder has a sleave on

[spenc]

3 minutes ago, WIMorrison said:

Personally I would cut a slot in the chassis to allow the decoder to sit inside it , that way it would be clear of the body shell. I would also insulate the end of the blue, white and yellow wires properly.

 

Also Sellotape isn't a good way to hold things on 

 

3 minutes ago, WIMorrison said:

Personally I would cut a slot in the chassis to allow the decoder to sit inside it , that way it would be clear of the body shell. I would also insulate the end of the blue, white and yellow wires properly.

 

Also Sellotape isn't a good way to hold things on 

The sellotape is only temporary until I pop and get some insulation tape.

[Izzy]

1 hour ago, spenc said:

It's hard wired no plug and socket decoder has a sleave on

  

Yes, I see that now. In which case seeing as it's a pre-DCC ready chassis it's really a case of going back to the start and re-doing everything again. With only four wires/connections it has to come back to the fact the body is breaking one of those connections when it's fitted, or is causing one of the motor feeds to touch the chassis. That can be goodbye to the decoder so must be avoided at all costs.  As the track connections are being made by connecting the black/red feeds to the chassis screws I'd check them first. The plug is plastic so it may be preventing constant connection under pressure. But also make sure those soldered connections to the motor can't press against the chassis in any way. The wire insulation stripped back too far.  Often these problems can be the silliest little thing.

 

Bob

[peterm1]

My two pennarth is that those motor connections look really dodgy. I'm inclined to think that the body presses one or both in to the chassis. Get practising with soldering to make those connections a lot neater is my advice, and make sure they're insulated from the chassis.

[spenc]

6 hours ago, peterm1 said:

My two pennarth is that those motor connections look really dodgy. I'm inclined to think that the body presses one or both in to the chassis. Get practising with soldering to make those connections a lot neater is my advice, and make sure they're insulated from the chassis.

Yes looking at the photos they don't look very good,today I am going redo it trouble is part of my health issues is I have reynauds and shakey hands I'm not as good as I used to be.

[peterm1]

Join the club with shaking hands.  Really annoying when I'm trying to solder wires to a decoder.

 

Sorry to hear you have that horrible disease.

[34theletterbetweenB&D]

Now I have seen the pictures the problem is clear. It's split chassis, and these require great  attention to insulation. That I can see solder on a motor terminal connection is enough to potentially explain the problem.

 

It was difficult enough in RTR OO. I always cut clearance into the chassis halves around the motor terminals because the terminals were intended to bear directly on the chassis halves with spring assistance, and  there simply wasn't space to put heatshrink insulation over the wire insulation, soldered joint and all the exposed metal of the terminal without first creating space. Cutting space for insulation led to a second problem, the mazak Bachmann used took a razor edge when cut, and would slice through the insulation, no trouble. It was a pig of a job in short.

[spenc]

21 hours ago, 34theletterbetweenB&D said:

Now I have seen the pictures the problem is clear. It's split chassis, and these require great  attention to insulation. That I can see solder on a motor terminal connection is enough to potentially explain the problem.

 

It was difficult enough in RTR OO. I always cut clearance into the chassis halves around the motor terminals because the terminals were intended to bear directly on the chassis halves with spring assistance, and  there simply wasn't space to put heatshrink insulation over the wire insulation, soldered joint and all the exposed metal of the terminal without first creating space. Cutting space for insulation led to a second problem, the mazak Bachmann used took a razor edge when cut, and would slice through the insulation, no trouble. It was a pig of a job in short.

When I brought it, it had a decoder already done but would not work so that's why I got a new one and I just copied the wiring,the wire's soldered to the motor terminal is were its supposed to be, on closer inspection the chassis block has already been cut back. today I will strip all down because even though it ran with the body off yesterday when i redone it there's a short with it now and I had to just walk away from it so hopefully today it will work.

[Andacami]

If struggling, maybe your local modelling club can help; I'd be happy to, but you are a long way from North London I'm afraid.

 

I think as said, once rewired with consideration to the shorting issues inherent, it'll be fine 👍