# Overload - but working loco, working DCC module?



## aeberbach (Apr 11, 2016)

I'm getting an overload on my Hornby Select DCC system and no action from a loco that seems to be OK coupled with a DCC module that I know is OK.

I have a new loco, Roco 72886 F Class - I bought a new Hatton's 8-pin DCC module for it but it did not physically fit. So instead I took my Hornby R3261 Class 08, removed the Hornby 8-pin DCC module that had been working in it, and put the Hattons module in it instead. Physical fit OK, Class 08 works just like it should with the Hattons module.

Then I put the Hornby DCC module into the F Class - as soon as I put the loco on the rails the motor moves very slightly, the controller shows overload and the cycle repeats itself every second or so.

Ouch I thought, bad loco - because I know the DCC module is OK, it was just working in the Class 08. So I put the blanking module back in expecting it not to work - but in analog mode it drives perfectly, forward and reverse. So the loco isn't bad. 

Then I must have put the DCC module in the wrong way around? Nope. Square pin is pin 1, lines up with the asterisk on the Roco PCB, same as the dot on the blanking plate used to.

I have isolated the track by connecting one long straight to the short Hornby "power rail", nothing else is on it.

Any suggestions?


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## DonR (Oct 18, 2012)

The decoder would isolate a shorted motor from
the DCC controller and likely die. Your test in
analog shows that the motor is fine.

Since you are getting an
overload indication on your controller it would
seem you have a partial short on the primary (track)
side of the decoder. That decoder may have gone
defective. It may be helpful to try it in another
loco now. If the result is the same the decoder
has gone bad. Since it's all electronic I doubt there
is a way to test the primary for a short.

Is there a possibility that the motor or light wires were
contacting the frame if that has a path to the track?

Don


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## aeberbach (Apr 11, 2016)

No chance of a short, in fact I put kapton tape around the electronics and the connector isn't close to anything conductive. Nothing appears wrong through a magnifier.

Fortunately I have another one - a starter loco in the Somerset Belle set has a controller. It's a four-pin connection (X9659) but uses the same DCC module as the 8-pin (R8249). Interestingly the 8-pin sells for 14 pounds while the 8-pin sells for 10 pounds - maybe save some money in exchange for a bit of fine soldering? I'm going to wire it up tonight and see how it goes.


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## aeberbach (Apr 11, 2016)

Well it's a strange thing. The speed controllers are all fine. The Roco engine though, for some reason had the DCC connector wired so that one of the track pickup wires goes direct to motor output. When I isolated the circuit board in the train and connected a DCC decoder between track and motor the way the standards say it should be wired, perfect operation.

Maybe it's just this one that slipped through QA. Anyway, fixed now, and better than a long return process.


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## Cycleops (Dec 6, 2014)

Thanks for sharing that info, glad you got it sorted.


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## aeberbach (Apr 11, 2016)

Oh, one more thing - the DCC module that Hornby sell as a four pin for less money _is_ the same as the eight pin, just with a different plug on it. I rewired it and it works fine with the eight pin plug (made from an 8-pin DIP IC socket with machined pins).


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## Cycleops (Dec 6, 2014)

The one thing I've discovered with decoders is that they're not all born equal. You get the best slow speed performance with ESU and Lenz. NCE are creditable but the wires pull out of the PC boards if handled too much.


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