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Union Mills N gauge conversion





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#1 confused.com

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Posted 16 September 2010 - 17:11

A little while ago I posted here asking about fitting a decoders into the N gauge motorised tender. There is very little room, and of course once the tender body is in place you can't see where the spare room is. A suggestion was made to remove the coal and sit the decoder on top of the motor, but I did not want to do this as it might devalue the loco if I decided to sell it.

So I purchased a Dremmell hand drill with milling tool and had a go. The UM loco is an LNER J25, which uses one of the smallest tenders, so less metal needs removing than the larger ones. Its from the current production run - there are older mechanisms which aren't as compact and will need a different approach.

Taking care not to catch the axleboxes with the shaft of the drill, I levelled the inside of the rear of the tender. Is just possible to do this without making the casting too thin or doing straight through. Make sure all of the swarf is removed.

Snip the capacitor wires where they are soldered to the motor terminals, and remove the black wire from the loco. I decided to unsolder the wire that was soldered to the case of the motor as it was making contact with the side of the body.

After a bit of experimenting I settled on a Digitrax DZ125 IN decoder. I tried a wired one, but it flopped down and rested on the motor worm. The decoder pins sit on the top of the motor (insulated by tape) and being ridged the hold the decoder in place. Some precision soldering is required but I managed to wire the decoder in without letting the smoke out. Pin 1 to the terminal which used to go to the motor, Pin 2 to the terminal that used to be grounded to the motor casing, Pin 3 to the loco and Pin 4 to the motor casing. Place some tape over the top of the decoder Pins and down the side of the motor to hold the decoder in place, then another piece on top of the decoder. Program on a test track and then replace the tender top. The first loco took an hour, subsequent conversions took 30 minutes. The photos were taken half way through conversion.

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#2 ian b

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Posted 11 November 2014 - 21:52

This may sound like a silly question but where do you solder the feeds to? There's obviously the lead coming from the loco but where does the other pick up from? I realise it's the motor casing lead but where do I attach it?

I've just bought an early B12 with a worm at one end so it looks like there's enough room for a dz126 anyway!

Edited by ian b, 11 November 2014 - 21:54 .


#3 confused.com

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Posted 12 November 2014 - 18:28

Looking at the 3rd photo you can see some solder on the motor casing, just above the centre wheel. Before conversion the suppressor was soldered there, so I removed it and used a spare length of decoder wire which became one of the rail feeds. The other wire screws into the loco body - changing it for a thinner shorter wire looks better.

 

Tim


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#4 ian b

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Posted 12 November 2014 - 21:19

Thanks Tim- spot on!

#5 OFFTHE RAILS

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Posted 24 April 2017 - 13:35

This is a very useful thread. I hadn't considered buying a non-DCC ready Union Mills loco due to the potential decoder fitting difficulties in such small models. 

After reading this thread I plucked up the courage to buy a Union Mills 2P and fit a decoder.

In the case of the Midland 2P 4-4-0 the tender does not need any carving to clear the Digitrax Z125IN decoder.

Ian









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