merchant navy class loco

[96RAF]

I have R1038 red boxed set with MN US Lines and that loco was DCC-Ready. Circa 2006/7.

I fitted a decoder by simply plugging it in in place of the blanking plug. Picture shows the socket location.

Since then it has been retro-fitted with TTS and a cube speaker as shown here...

 

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[Chrissaf]

Treat the capacitor across the motor as optional when converting to DCC. Some remove it as a matter of course, some leave it in situ, well at least until they have an issue caused by the capacitor presence. There is some forum evidence to show that some of these capacitors can go 'short circuit' which is very likely to be one cause of a decoder emitting smoke and dying.

 

I strongly suggest that you use a multimeter, set to measure resistance, and look for a short circuit across the motor before burning out any more decoders. Note that you should use the actual measured resistance scale of the meter and not a meter 'continuity buzzer' feature. The reason being is that the measured DC resistance of a motor can easily be less than 100 Ohms which can sound a 'continuity buzzer' and that would give a false indication.

 

Assuming it is a Hornby 8 pin socket 'DCC Ready' loco then with the 'DC Bypass' plug and the 'Decoder' removed. Use the meter to prove all the basic wiring connections to the socket [see image further below]. I make this suggestion because there is also forum evidence to support the issue of some Hornby loco products leaving the Chinese factories with 'cross-wiring' faults. These faults do not so up when operating the loco on DC Analogue, but instantly blow a DCC decoder when powered up on DCC track.

 

These wiring faults can usually be observed as a cross wiring that swaps the motor and wheel pickup pins on one side of the 8 pin socket [For example; Pin 1 crossed with Pin 8 or Pin 4 crossed with Pin 5]. This does not affect DC operation, but connects one side of the decoder motor output circuit directly to DCC track voltage. It is this specific cross-connection that blows the decoder.

 

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• With the meter, what you are looking for is that there is no short between Pins 1 and Pin 5 nor Pin 4 and Pin 8.
• Also, that there is continuity from the 'left and right' wheel pick-ups to Pins 4 and Pin 8 respectively.
• Also, that there is continuity from the 'right and left' motor brushes and Pins 1 and Pin 5 respectively.

 

Hope this helps to narrow down your decoder damaging issue.

 

PS - You really should have started your own dedicated thread rather than resurrecting this old one.

 

TIP: As a newbie poster on the forum, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

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See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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[ColinB]

As well as doing all the checks Chrisaf recommends what I also do is put it in programming mode and see if I can read the address, or manufacturers id. At least in programming mode there is less current going into the loco. The other thing I do is put the loco on the track, remove the controller from the track and DC header from the loco, so you just have the socket. Then check if pins 1 or 5 are connected to the track, if that is the case then you have wiring fault. Depending on the motor you should read a value between pins1 and 5 which will be greater than 10 ohms and probably less than a 100. It could be of course that the decoder just touched something metallic when you put the loco together, especially if it was a Hornby decoder that doesn't have any insulation. I have done that lots of times.

[kiwitommo]

Thanks for the above suggestions regarding circuit tests etc. Whilst feeling a bit miffed about letting the smoke out of that decoder, it could have been worse: I have a newly-purchased TTS decoder I had planned to install, but thankfully fitted an old cheap decoder instead as it was closer to hand. It certainly has not been a good introduction to fitting dcc to my first British loco, having successfully fitted dozens of decoders to my US fleet this has come as a disappointment. Correction, second loco: the first was a hard-wire install into United States Line which I did over the weekend. That one works fine and runs smoothly after correcting a slightly bent eccentric crank. PS: I have just run the meter across the above mentioned terminals, sure enough there is a dead short across two of them. (Couldn't tell you which two, as un-helpfully terminal one has not been marked as per NMRA practice) So I now have a choice, either correct the wiring on the socket orhard wire the decoder. If I knew which terminalno.1 was I could follow the above diagram and re-wire the socket, but as it isn't marked...

[ColinB]

Just make sure pins 1 &5 go to motor and 4 & 8 go to track. It does really mater if they have not marked pin 1, because for these wires it is symetrical. You only have to worry if you start adding lights. So if the socket is upside down pin 5 is pin 1, pin 1 is pin 5 so no issue really. There might be a square around the pin on the PCB to indicate pin 1, or a dot. Sadly, this has become a thing you seem to have to do with each new loco from Hornby, Bachmann and Dapol ones seem ok, but they tend to use 21 pin sockets which forces you to design your electrics a lot better. If it was a brand new loco, Hornby owe you a new decoder.

[Chrissaf]

There are only four wires to worry about, thus it is an easy matter to confirm which pins connect to the four possible end points [namely the left side of the motor, the right side of the motor, the left pick-up wheels and the right pick-up wheels] using the meter. Draw these connections out on a bit of paper and then compare them to the schematic in my earlier post. They will either match the schematic, or match only at one end if incorrectly wired at the factory with crossed pins. Given that you say you can measure a short circuit, then the likelihood is [guesswork on my part as I don't have the benefit of looking over your shoulder and seeing what you can see] that the short is across Pins 1 & 5 and you have a short circuit capacitor across the motor. In which case just 'snip' the capacitor off and see if the short goes away.

[Fishmanoz]

Might I start with one step back from fault-finding mode and confirm that all that is necessary to convert Hornby DCC Ready with socket locos to DCC is to remove the blanking plug and install the decoder. Nothing else needed.

 

Therefore, if the decoder has blown by doing this, then there is a fault somewhere. Possibilities, some already mentioned, are:

 

-  The capacitor across the motor terminals has gone short.  My advice is always remove such capacitors (or inductors in series with one motor terminal).  They are suppression capacitors for DC and not needed for DCC.

 

-  You May have pushed the decoder in too far such that one of the pins (would be a motor pin on the end of either the orange or gray wire) has touched the chassis behind the socket. Check and insulate behind if you can But don't push it in so far.

 

-  There is a wiring fault in the socket, not unheard of.  Check as described by others above.  If so, you have a claim on your supplier. You could return it faulty but unlikely they have another. Or you could discuss fixing the wiring and replacing the decoder.

 

Colin, May be be brand new boxed but still around 15 years old as these sets were manufactured around 2005 for 3 years only.

[ColinB]

I think he established in his last post he had a short across two pins. Easily done those 8 pin dcc socket boards are terrible to solder to, I have done it loads of times, but I normally catch it when I do my final tests. I did ask if it was a new loco, obviously not.

[Fishmanoz]

Oops, so he has.   Shouldn't be too hard to find given all the info on here, whether it's a shorted capacitor, swapped wires to socket or solder bridge between pins on the socket.

 

Whichever it is, it's a warranty claim against the supplier for any of those three, or Hornby should also wear the latter two.  Either of these two could have been there since Day 1, worked fine on DC and only found now on conversion to DCC. 

[96RAF]

... worked fine on DC and only found now on conversion to DCC. 

 

Common enough problem Fishy and discussed many times on the forum.

[kiwitommo]

Thanks for the resposes chaps, I did try responding yesterday but in a move which can only be described as "brilliant" this forum only allows new members two posts per day...I am guessing instigated by the same Hornby person who decided that not testing dcc sockets at the factory would be a "brilliant" idea?

Further inspection has revealed a solder bridge across two adjoining sockets. When I muster the energy (night shifts killing me at present) I will take a soldering iron to it. It was quicker to hard wire the decoder into the older MN than all this messing about. So, will I be moving away from American models anytime soon?( I think you can guess the answer)

[Chrissaf]

The two post limit only applies for 24 hours. You should be able to post freely now.

 

The limit was introduced because the sign-up process for this forum does not seem to have any 'anti-spam-bot' technology and the forum [prior to this 2 post limit] was regularly inundated with pages of duplicate spam posts created by automated Internet bots.

[kiwitommo]

I finally sorted this loco out, It was easier to just trim off the wrongly-wired socket and hard wire the decoder. I applied some weathering and got it outdoors this afternoon in a brief spell of sunshine, here it is pictured with the only other Bulleid Pacific I owned until recently. (A heavily modified Airfix kit with number and RAF shield yet to be applied)

Sorry, couldn't upload the image as it appears this forum does not allow iPad images!

[96RAF]

To upload an iPad image, open it as usual in Photos, edit and markup if required, then send it (up arrow in a box icon) to Files on the iPad.

iPad will ask where to save it - I just park everything in acrobat, but you can make named folders to suit. This will also convert it from Apples clever new photo format to something more universal.

Now when you click on the photo upload icon on the forum, choose browse and navigate back to the image saved in Files-wherever. This image will upload if less than around 2Mb.

[walkingthedog]

And it works every time..

[kiwitommo]

Ok thanks, I will put my limited skills to the test.

[kiwitommo]

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[kiwitommo]

Test 2

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