Digitrax DN136D decoder installation

Having looked around the forums, there doesn’t appear to be any references to inserting a DCC chip in the above Model.

I bought this as a used item from Rails of Sheffield via an eBay auction, prior to even considering going DCC.

It’s reputation as a ‘growler’ (noisy motor) being fully justified, I still like it and looking at the general condition and especially the motor, it looks like it’s hardly been used.

I took it apart on Wednesday and my initial thought was that I wouldn’t be able to fit a decoder, so I’m going to have to sell this and that will be a real shame.

 Checking the Bromsgrove Models decoder Instructions for the umpteenth time and watching the linked Wordsworth video for the Hornby version yet again, I decided I’d have another look.

From what I’ve read, the Airfix/Mainline/Dapol versions are all the same and Hornby now have the tooling, which suggests the only changes from the original version are the motor mountings and connections. Certainly the Hornby version in the Wordsworth video looks remarkably similar to my Dapol version.

 I was fortunate enough to have the locomotive instruction sheet which details how to remove the body (screw front underside just behind the front coupling) and the motor for brush replacement (screw under the rear truck).





The model is a classic wheels insulated on one side so that the chassis is the opposite polarity type.

The wheel pickups to motor connections are copper (at least I think they’re copper) sprung strips, one attached to the weight at the top of the chassis pressing on to the top motor brush contact, and the other at the bottom of the left hand side (looking forward) of the motor housing, which presses on a another copper strip running under the motor to the other brush contact and slightly up the other side to enable a capacitor to be soldered across the contacts.

It turned out that decoder installation was quite simple, if a little fiddly.

The only place I felt even a very small decoder would fit is the underside of the cab roof.

I removed the motor and then de-soldered and removed the capacitor

I then shortened the copper contact attached to the weight so that it would no longer touch the top motor contact.

I also shortened the copper contact on the bottom of the motor, so it no longer reached the bottom motor contact in the motor housing; however this leaves only a very small air gap.

I used a Digitax DN136D decoder which comes with 4 1/4” (108mm) wires, which I didn’t shorten.

Apologies for some of the following pictures but the camera batteries were dead, so I had to use my phone yesterday and it was a rather dark afternoon, the only additional light being the room lights and a desk lamp.

There’s no room in this model for any functions such as lights, so after cutting all the unnecessary function wires short I soldered the decoder wires as follows:-

Red to shortened copper strip on the weight

Black to the copper strip protruding from the bottom of the left hand side of the motor housing



Orange to the top motor brush copper contact strip, where I removed one side of the capacitor

Grey to the side motor brush contact strip, where I removed the other side of the capacitor



fairly simple really as it turned out.



Since as mentioned, the air gap between the wheel pickup contact strip  at the bottom left of the motor housing and the now shortened bottom  motor contact strip is very small, I’ve inserted a thin piece of  Plasticard (Styrene) held steady with a bit of Blu-Tack, just to make  sure there is no contact between the two.

Once the body is put back on, the Plasticard strip isn’t going anywhere but I might revisit this to make a better job of it later on.

I also stuck a bit of insulation tape over the wires to try and keep them out of harms way when putting the body back on.







It works fine, but the wires are very visible through the cab sides, so I’ll need to tidy it up at some point.



At least I now have my suburban passenger service motive power along with a DMU and the Hornby Thompson L1 and Bachmann V3 (which isn’t available yet) can remain on the wish list for a bit longer.


Ed


PS Anybody want to buy a Bachmann J72 from circa 1995 with split chassis, as I ain’t fitting a decoder in that!

Hi Ed,

Nicely done. Those Digitrax N-scale decoders are quite useful for small spaces. Not sure all those high capacity wires that were originally used are necessary, as they're only carrying 15-17 v AC and 1 amp at most. Throwback to motors that needed a high start voltage to get them going. Not necessary with DCC as it's always at high voltage. Digitrax wires are also oversized for what they do as well (check out the wire gauge on a LokSound ESU for example). I normally bin original wires and replace them with something a lot smaller and a bit more flexible. AWG 18-19 is fine for around 2 amp continuous transmission.

That J52. :chickenSend the chassis over and I'll do the wiring for you (I don't need a J52). I've run out of split chassis UK engines, need one to write up. If you want it chipped I can do that as well. PM me.

Nigel

Hi Nigel

The decoder is rated at 1Amp/1.5Amp max and I don't know what the stall current of this old motor is, which is one of the reasons why I selected it.

The wires are pretty thin and flimsy, but I have no idea what AWG they are. I'm sure I'll be able to tidy them up a bit so they're less visible .

Thanks for the offer but it's a J72 not a J52 I was half jokingly offering for sale. It is possible to install a decoder and it's a very similar job to this:-

Bachmann J39 - split chassis - DCC Fitting Guides - RMweb

Having taken the J72 apart to have a look, cutting the ends off the motor terminals to ensure the body could be re-fitted looked to be very fiddly and not worth the effort.

I'm not that worried about keeping it and it has a missing hand rail (which I know I could repair), but it could be useful for someone not converting to DCC.

I may consider putting on eBay, or just put it in a display box on the shelf so you can't see the side with bits missing.


Ed

Nice job Ed. :thumbs 

Forgive me if I'm wrong, but could the decoder be placed in the smoke box ? Or is it a case of no place for the wires between the body and chassis weight ??  With hiding the wires, could you perhaps paint the visible sections black, leaving the ends coloured ??

Interesting to see the locos numbers show through to the inside of the body in your third pic…

Cheers, Gary.

 

Hi Gary

It's difficult to make out from the pictures, but the smoke box is solid plastic. There is an gap under the front of the boiler where you can see daylight, so I don't really want to see a decoder instead and the weight on the top of the chassis is an almost perfect fit to the underside of the body. Probably feed some wires through, but not enough room for even the thinnest of decoders.

Interesting you mention painting the visible bits of the wires black, I read somewhere about doing that on a different conversion. I might try that and/or adding a crew as there is a bit of space where I stuck the styrene shim.

The loco number isn't actually showing through the body, it's almost like it's been printed on as a mirror image, but only on one side.

Very odd :???:

But it is a pretty old design.


Ed

Hi Ed,

As long as it's not a B52.

Nigel

It is a good looking loco Ed.  From the looks of the motor, I wonder if it came from the Airfix stable?

As for fitting decoders to split chassis locos, I positively refuse to do it - I've done 3 where the operation was a success but the patient was never the same afterwards.

John

 

Despite the modern trend to an isolated chassis and a more prototypical "open" look on steam engines, split frame designs do have some advantages: No electrical pick-ups for starters. Plus a nice weight/volume ratio and a low COG (try a Comet chassis under a plastic steam loco' body and you are soon reaching for the lead weights). Disadvantages: They often come with dodgy (and often split) plastic split axles. Older Bachmann 4-6-0's are notorious for this, and the replacement wheel sets only fit the more recent models. I've binned 3 older GWR/BR Manors over the last 5 years because of perished split axles. Plus converting a split axle OO design to EM gauge is a somewhat interesting process (as in "may you live an interesting life", mine's too short so I don't). The hard-to-get-at motor and intermediate spur gear is fiddly to get positioned correctly (keep it in place with the appropriate grease), and their really weak point, plastic insulating frame bushes that with age get brittle and break the moment the frames are split. Luckily replacements are available (from either Bachmann Europe or Bachmann USA). 3-hands seem to be required when reassembling them (but only 2 when disassembling them!). I use a large, deep tray as bits tend to go flying when working on them.

I recently converted 3 Bachmann split frame diesels to DCC, they all run sweetly, although I had to replace the frame bushings on one of them. With the body shell on impossible to tell whether they have a modern isolated chassis or a split chassis. Working on N-scale split chassis' is a bit more challenging, but not difficult.

Nigel