Weird decoder problem

[Colinw62]

Hi

 

Here's a weird problem I'm having with a decoder in a loco. The loco will run perfectly but if there is a short or an interuption of power the loco will stop and all lights flash (red and white at both ends). The loco/decoder will not respond to any commands and will not even respond to the "stop" command from the system. The only way to recover the loco/decoder is to lift if off the track, then place it back on again. The loco will then respond normally until a break/short/stall is encountered.

 

Any ideas???

 

The loco is a Bachmann Class 66.

Decoder is a Lenz (not sure which but I'll check and update the post).

System is NCE (both Power Cab and Power Pro 5amp systems)

 

ColinW

[RFS]

Flashing the lights is the way a Lenz decoder will indicate it has a short circuit. Lenz decoders have short circuit protection and if there's been a short it will indicate so in CV 30. However I don't know why the deocder is detecting the short before the NCE system cuts the power.

[Nigelcliffe]

The Lenz behaviour is supposed to occur on detecting a short within the loco, in the motor or through the lights. In theory, it doesn't happen if the loco causes a short at the wheels, for example derailing or running the wrong way through turnouts.

 

So, either there is a fault occuring within the loco, or the loco wiring is a bit squiffy, or there is an interesting interaction between this Lenz decoder and the NCE system.

 

Does the fault occur when the loco runs through particularly tight track, such as reversed curves, or very tight turnouts ? That might indicate an internal wiring fault only when in a particular alignment.

 

- Nigel

[Colinw62]

Hmmm some interesting feedback so far.

 

Only had a quick chance to try and read the decoder and the chip was playing silly beggars with me!! It gave a different Manufacturer ID each time I tried to read it, 8, then 16...then I noticed the lights flashing as it stood on the programming track. I did get to see a version number which was 78 each time, which if I'm correct could indicate a Lenz Silver chip - highly likely as I've bought a few of these.

 

re: does it happen on tight track etc.. Nope it will do it on a straight section, it almost seems random. It runs fine for a while then will stop and the lights flash.

 

I think the idea of a wiring problem somewhere in the loco is a good one and I'll investigate further when I get more time. I think I will start by removing the chip and see how it performs on DC and take it from there.

 

As always, thanks for the feedback.

 

Colin

[Edwin_m]

Trying it on DC is a good idea as one cause of decoder overload could be a faulty motor which is drawing too much current. I've seen this on Farish 66s and heard about it happening on some other Bachmann motors. To check for it definitively you need to measure resistance across the motor contacts with the armature in various positions.

[Colinw62]

Thought I'd post an update on this issue and hopefully a resolution!!

 

Being "challenged" by electrickey, multi meters, soldering and small fiddley wires I decided to seek help from my friend David Page (Railway Dave).........well I gave him the loco to look at and updated him on the feedback received to my post.

 

The suggestion of an on board short was a real help and I think gave a starting point.

 

When David dismantled the loco he noticed a wire had been trapped between the metal chassis and the loco body where the body fixing screws locate.

 

I've attached a couple of pictures which illustrate the damaged wire and where is had become trapped. There are some channels along the edge of the chassis which I guess are wire runs, however the wire did try and move itself back to the point it had become trapped when free so it has been taped out of the way. Despite making sure wires were out of the way when reattaching the body after fitting the DCC chip, I guess the wire just moved itself back in the last moments when the body was fixed back to the chassis - something to watch out for in the future!!

 

So far the fault has not occured again. We are at Nottingham Show this weekend with our layout "Brenton Midland" and 66077 will be getting a run out, a good opportunity to see if this has fixed the issue.

 

Coincidentaly, I also had a problem with another Bachmann Class 66 that was only picking up power on one bogie. This loco had exactly the same fault, a wire trapped in the same location and broken as a result!!