Fitting a DCC decoder to Hornby R9287 0-6-0 Thomas

[Art Dent]

Fitting a DCC Decoder to Thomas

 

Removing the body.

 

The body is basically clipped in place.  There is a single central plastic clip at the rear of Thomas' body (behind the buffer beam and beneath the bunker) but to access the clip, the rear coupling must be removed first.  The complete body is retained by this single clip (which is quite stiff to spring) and the two lblack 'lugs' at the front beneath Thomas's face.

 

The screwdriver shows its location of the screw which retains the coupling.

 

 

 

 

Remove this screw to gain access to the clip which retains the body.

 

 

 

 

Once removed, the plastic clip is accessible.

 

The following picture shows the clip (circled).

 

 

 

 

The clip is 'sprung' by a small, flat-bladed screwdriver placed between the rear of the body and the chassis.

 

If the end of the screwdriver is pushed towards the rear, the clip will spring and the screwdriver tip will lift the chassis off the clip.

 

 

 

 

There are two small locating lugs at the front of the chassis, lift the rear of the chassis and, holding the body, pull the chassis rearwards - the lugs will release and the chassis can be lifted out of the body moulding.

 

I was curious to see how much room there was inside Thomas's body to allow for fitting a decoder and/or stay-alive.

 

The upper part of the boiler (rearward of the smokebox) and cab is clipped in place.

 

From the underside it LOOKS like it is a simple matter to unclip the top of the boiler - however this moulding is held in place by the cab - so the cab must be removed first.

 

There are two clips on each side of the cab which hold the cab in place.  Two of the clips are obvious however the two smaller, rear-most clips are rather difficult to see and access - a small flat-bladed

screwdriver does the job however.

 

 

 

 

Once the cab has been removed, the top of the boiler can be removed.

 

There are two (quite obvious) clips which hold the moulding in place together with a 'lip' at the front which fits under the main body moulding just rearward of the smokebox.  These are shown in this picture.

 

 

 

 

There is plenty of room in front of the motor as can be seen here.

 

 

 

 

There seems to be plenty of room behind the motor too ...

 

 

 

 

... tons of room to fit a decoder in here?

 

However, there isn't as the boiler top moulding (which includes the boiler backplate) fills the gap as can be seen in this next picture.

 

 

 

 

You could drill a couple of holes (slots would be better) at the base of the backplate where a decoder's wires could be threaded through.  It looks like there is a gap here - but there isn't as it closes up when the cab is snapped back into place.  Alternatively a small amount of the cab side (just below where it says 'L-6118' in the fifth picture) could be removed as it is this that blocks the gaps at the sides.

 

 

 

 

When viewed from the side, the motor, the two inductors in the motor feeds and capacitor are hardly visible.

 

This means that there is around 3mm more space between the top of the chassis and the bottom of the boiler moulding than you can see here.  The top of the boiler does have a very small radius however.

 

 

 

 

This picture shows the space available for the decoder and a stay-alive in the forward part of the chassis.  Indeed Hornby themselves suggest this is where to fit a decoder.

 

 

 

 

Pickups and motor connection (LHS) ...

 

 

 

 

Pickups and motor connection (RHS) ...

 

 

 

 

Note the awful plastic surround to the motor.  It may be great for insulation nut you have to be very careful when using a hot air-gun on heat-shrink!

 

View of the top of the motor showing the two inductors (which are encased in black heat-shrink sleeving) and a suppression capacitor (the round brown component).

 

It is easy to tell inductors apart from capacitors (even though Hornby call all three of these components capacitors) because the two inductors are wired in series with the motor connections whilst the capacitor is connected in parallel, across the motor connections.  Capacitors are never wired in series with the motor as they don't pass DC current!

 

 

 

 

Contrary to what Hornby tell you to do, you do NOT need to unsolder the motor connections from the pickups.  The following picture shows where to cut on the left hand side ...

 

 

 

 

... and on the right hand side:

 

 

 

 

Cutting the pickup leads as indicated means that you don't have to make a solder joint close to the plastic motor housing (!)

 

 

 

 

Once you have made these two cuts, unsolder the capacitor.  The two inductors and capacitor are NOT NEEDED for DCC operation and can be discarded.

 

 

 

 

As you can see, two of the 'capacitors' as Hornby refer to them are indeed wire-wound inductors!

 

The easiest way to unsoder the capacitor is to lift the chassis by the capacitor using a pair of pliers.  The weight of the chassis will pull the capacitor away from the motor lead once the solder softens.

 

First one side ...

 

 

 

 

... then the other:

 

 

 

 

Now cut the two motor leads about 5mm from the MOTOR SIDE of the inductors.

 

Your chassis should now look like this:

 

 

 

 

I like to hook the end of the leads over to provide a good positive contact area for the decoder leads:

 

 

 

 

There is a small groove at the front of the chassis. In the instruction sheet that comes with the loco, this is, in fact, where Hornby suggest the decoder goes - IF your decoder is small enough!

 

 

 

 

Hornby Service Sheet showing suggested decoder location:

 

 

 

 

If you have a small enough decoder - such as the 6-wire LaisDCC 860012 Decoder (+ 2 stay-alive wires) - it can sit on its edge in the groove.

 

 

 

 

Heath-Robinson Test Wiring:

 

 

 

 

I always like to check that things are working (even better if they are working as expected) before tidying up the wires and applying heat-shrink.

 

I prefer to leave the decoder wires as long as originally supplied just in case I ever decide to use the decoder somewhere else.  That is, of course, assuming there is enough room between the chassis and body to store the excess wire!

 

The completed installation.

 

Notice the black and blue wires (for attaching a stay-alive).  I tried TWO different stay-alives with the LaisDCC Decoder and it didn't play nicely with either - so after this picture was taken they were duly insulated and heat-shrinked.

 

Having blown up an expensive Zimo sound decoder whilst testing during an install, I have learned the hard way to insulate everything - every bare wire.  Don't assume that simply cutting the end off is enough - it isn't.  To ensure no possibility of shorts, I cut adjacent wires to slightly different lengths before bundling them up and heat-shrinking the lot.  No more tears since I adopted this practice.

 

 

 

 

Hope this helps.  It really isn't too difficult a job to do - just make sure that you have a good pair of cutters, a good pair of pliers, electrical flux and rosin-cored electrical solder (don't use plumbers solder or plumbers flux) and a decent soldering iron (I use a 140W Weller Soldering Gun with the tip filed down).

 

A steady hand and a good pair of magnifying glasses especially in my case) helps enormously.

 

Cheers,

 

Art

Edited January 13, 2019 by Art Dent

[Ken H]

Thank you for this excellent answer to my problem.  I was convinced that I needed those inductors (labeled capacitors), but my R30039 Thomas didn't have them.  Now I know why.

One Question:  In the Fig. 8 above, you show the 104 Capacitor still in place.  Will that hurt anything?  You said it wasn't needed for DCC.

 

I'm installing a Digitrax SDH167D sound decoder which also converts the 0-6-0 to DCC.  There is plenty of room in that boiler.  This should be fun.

 

I'm adding it to my On30 stable.  A friend will change the cab for a larger one, and it should look good as a left over WW1 loco.

 

 

Edited August 10, 2023 by Ken H

[Ken H]

Day Two:

 

I have now pretty much finished figuring out how to fit that Digitrax SDH167D sound decoder into the OO Hornby 0-6-0 Thomas.  A lot of wires hanging out to cut and replace.  Thank God for your article' Art (and the art in your article)

 

See below how it stands now.  The speaker (a nice 8 ohm one that comes with the Digitrax decoder) will go in the bunker under the wood.  The 330uf keep alive will hide in the boiler.  This decoder is big.  The decoder itself is double stickied to the Engineer's side of the inside of the shell, just clearing the wheels.  I'll paint any of the blue Digitrax shell that shows green.

 

Next comes figuring out which wire solders to which wire.  (Love how the British pronounce SOLDER the way it's spelled).  We Americans pronounce it with the L silent. 

 

Hope to hear from my friend who does great work making things out of other things.  He felt a On30 scale Porter cab (like my LUCY (named for my great grandmother) would be great (and has an extra one) but I think it would be too big).  Of course OO 1:76 scale cab doors are about 4' in O scale (1:48).

 

 

Boy, there are a LOT of wires.  Hope it all works.

 

Ken (in SoCal)

[Ken H]

Did the soldering today, and cut all the leads to a reasonable length.  Got out my Bachmann Command Control unit, and somehow got it to work in DCC.  I was able to get the 0-6-0 to run a bit, so the decoder definitely changed the loco to DCC.  Tomorrow I'll see about sound, when I run it as #3 on my On30 tracks using my NCE Power Cab.

 

Ken (in SoCal) 

[34theletterbetweenB&D]

On 10/08/2023 at 22:46, Ken H said:

Next comes figuring out which wire solders to which wire.  (Love how the British pronounce SOLDER the way it's spelled).  We Americans pronounce it with the L silent... 

...correctly. It was definitely spelled 'soder' up to C16th.

 

However classicists in England started getting all agitated over altering spellings to conform to Latin roots, with the insertion of an L the case of soder/solder. (In time past we got into det, and that was modified to 'debt', but in that case the pronounciation didn't alter, perhaps too awkward to voice 'debbed' or some such?)

 

Whatever, interesting idea of a cab transplant. 

[RAF96]

On 18/08/2023 at 10:13, 34theletterbetweenB&D said:

...correctly. It was definitely spelled 'soder' up to C16th.

 

However classicists in England started getting all agitated over altering spellings to conform to Latin roots, with the insertion of an L the case of soder/solder. (In time past we got into det, and that was modified to 'debt', but in that case the pronounciation didn't alter, perhaps too awkward to voice 'debbed' or some such?)

 

Whatever, interesting idea of a cab transplant. 

Wasn’t debt short for in debit.

[34theletterbetweenB&D]

48 minutes ago, RAF96 said:

Wasn’t debt short for in debit.

The root word from Latin was of that form, but the English had 'cut it down' to 'det' sometime during the unsupervised couple of centuries when  Norman French was in use by the great and (questionably) good, and the English language evolved with little scholarly input.

 

(We happily got rid of quite a lot more linguistic junk in that period by way of gender,  case and various other 'rules' of grammar, thankfully. I think there is one survival of grammatical gender in English, fair hair is blonde on a woman, blond on a man.)

[Ken H]

I love my converted Hornby "Thomas". 

 

 

One problem, it keeps killing DCC decoders.

[Ken H]

I have tried Soundtraxx Economi UK, and Digitrax SDH167D.  Both worked beautifully for a day and a half, and then died.  And this is before I added a 3mm headlight and tail light (both with resistors).  I'm now running using a Digitrax DH126PS.  It runs the Hornby fine, except I burned one out when a tiny component in it burned, and the lights went out.  But the loco kept running.  I've replaced the Digitrax with another DH126PS, and it is handling the motors and lights fine.  I just wonder if that 104 capacitor shouldn't be across the motor leads.  Something is killing my decoders, but it's taking its time.  Now my module group is wondering what I'm doing wrong.  I installed a MRC SOUNDER Steam Sound Decoder to add sound, since the Digitrax decoder doesn't do sound.  The Sounder did fine for 10 days, and then died.  It's on its way to New Jersey.  This is all taking place on my test track, powered by a NCE PowerCab.

Edited September 21, 2023 by Ken H
to correct a word and add content

[Ken H]

My thoughts about leaving the 104 capacitor in the circuit is because my Hornby 0-6-0 didn't come from the factory with the two inductors in series on the grey and orange leads from the decoder to the motor, but it did have the 104 capacitor in parallel with the decoder wires to the motor.  I've lost five decoders (two Soundtraxx, two Digitrax, and an MRC sound decoder) during this project, and I wonder if Hornby didn't feel the 104 capacitor was still needed.  I just installed a new capacitor and so far it runs on DCC, and the lights work.  I'll see if I lose any more decoders.