ROB’S RAILS            

Article 1 - Conversion of GW Pannier Tank to DCC Sound                     


Fitting sound to a Hornby R3122X DCC-fitted Pannier Tank running number #2773 should also be possible based on a photograph below, (originally posted on the Hornby forum by howbiman as topic headed - How do I get the motor unit out of this loco for servicing), but it may mean sacrificing the decoder mounting block on the front of the chassis.


The critical dimension is that the speaker enclosure base must sit flat on the main body sidewall steps so that the body top will clear the speaker, therefore the decoder mounting must not intrude into this space. Check with the body in place and the tank top removed.















R3122X #2773 Chassis (picture reversed from original)



There is insufficient room to install a standard DCC decoder socket in locomotive #2728 so the conversion is hard wired. It may be possible to install a smaller 8-pin socket (or utilise the 4-pin socket in #2773 variant), but as the speaker is also hard wired I didn’t see the point. The normal speaker wires are not long enough, so these are extended to suit. Where possible all wire connections are insulated with heat shrink tubing. White blu-tak was used to control wiring runs in tight places, but tape is equally suitable.


The decoder used is a very early Hornby TTS with the standard 28mm round speaker and enclosure. The sound set is of no specific locomotive, with many different whistles and the chuff rate seems to suit the Pannier. Don’t ask where I got it from – the only answer you will get is “...from The Tooth Fairy”.


Remove the coal load by turning the loco upside down and using a thin probe through the hole(s) in the back of the chassis push out the coal load. It is held by a central spigot on the back edge. Mine just fell out.


















Decoder Stowage, Coal Load Spigot Hole and Probe Access Hole(s)



Remove the body as follows – from the top of the coal bunker using a flat screwdriver blade carefully press the rear hook on the chassis forwards and down to release the body. The body will rotate about the two front hooks and can be carefully removed. See pictures of Back Hook and Front Hook below.



















Back Hook

















Front Hooks


Modifying the body - take the tank top slab off the main body. My handrails were loose, so I removed them and also levered the top up using a small screwdriver blade in these holes – see picture at top of page. The tank top slab has two spigots attaching to matching corner posts in the main body.


With the top off, trim the two corner posts flush with the main body floor and drill a 3.5mm (max) diameter hole through the funnel to let the sound out. Also remove and trim to length the two body side weights to make room for the speaker. The weights are just stuck down, so pry them off, trim to length and refit after mounting the speaker and routing the wires. Trim the top slab spigots flush also.


















Speaker Installation


The speaker is mounted in its usual plastic enclosure to maximise performance, (but with the two mounting lugs trimmed off). It sits flat onto the floor of the body sides. White blu-tack is packed into each corner to seal it especially where the wires exit and to hold it in place as pictured above.


If you don’t have an enclosure you can make one for a 28mm diameter speaker from the bottom end of an empty Humbrol plastic paint pot. The speaker wires need to be extended to reach the decoder so do this before mounting the speaker. Either unsolder at the decoder or speaker or cut the wires mid-way and splice a bit in. Sleeve all joints.


Run the speaker wires down the side (I used right hand) of the body weight area and into the coal bunker area, ready to reconnect to the decoder pads if your soldering skills are up to it, or more simply reconnect to the existing speaker wire stubs from the decoder. I had to trim the rear under-body away at this side to allow the wires to route without any chance of being trapped between body and chassis as shown below.

















Body Modification


Unsolder all wires and capacitors, etc from the motor terminals and wheel pickup strips, noting that as the lower motor terminal is fairly inaccessible, I opted to cut this wire about 1cm from the terminal, then solder the new decoder wire to it and sleeve the joint. If retaining the 4-pin socket on #2773 you will have to work the next bit out yourself.


Now the only real tricky bit – the sleeved TTS decoder only just slots into the coal bunker and the wires have to come down through into the chassis area. This means working with the decoder in the upper bunker area and the body close to the chassis. You need enough slack wire to be able to work and to manoeuvre the decoder into place later.


The sound decoder 8-pin plug is cut off, leaving the wires as long as possible and four of the wire ends are made ready by stripping back and tinning. This installation only uses the red and black (track), and orange and grey (motor) wires, so the other 4 wires can either be trimmed back and made safe, or as I did leave them long, make safe and sleeve, just in case I ever decide to use them in the future. They can be coiled up in the coal bunker.


Wiring up the decoder - feed the red (right pickup) and black (left pickup) decoder wires down the side of the motor and solder to the wheel pickup strips. Secure the wires to the motor using tape or blu-tak.




















Pickup Wiring


There is very little room between the chassis sides and the body so make sure your soldering is neat and the pickup tangs are pressed flush against the plastic motor block.


Solder the orange (motor top) and grey (motor bottom) decoder wires to the motor terminals using the lower terminal extension method as noted earlier.


If you have not already done this reconnect the speaker wires and sleeve the joints.


Secure all wires as best as possible out of harm’s way using blu-tak or similar.
















Motor Wiring


Test the installation at this stage with the body loose, including for correct motor direction and sound functions. I have a rolling road so it was a simple case of putting the chassis on the rollers, propping the body up safely and testing it all worked. Don’t expect too much quality from the sound with the body off.


When you are sure all is OK, re-mount the body to the chassis by engaging the two front hooks on the chassis into the front of the body, making sure nothing is catching (particularly the pickup tangs and stray wires) and rotate the body down onto the back hook at the same time safely routing and securing all wires. Click the body finally into place when you are happy no wires are trapped.


My decoder is encased in heat shrink tubing which is closely trimmed at each end. There is not much room in the coal bunker, but the decoder will rotate into place and slot down nicely if you get the lumps and bumps the right way round. The spare wires can be packed into any gap. See earlier picture.


All that remains to be done is to trim the inside of the coal load if necessary to clear the decoder and drop it back into place. The tank top clicks into place at the back and needs a bit of glue or double sided sticky pads or blu-tak to hold it in place at the front. Refit the handrails if previously removed.


Re-test the loco on track and adjust sound volume(s) to suit.


© Rob’s Rails 2015

Installing sound in a Hornby R1077 Pannier Tank

This article describes fitting a DCC sound decoder to a Hornby R1077 GWR Pannier Tank running number #2728. This model is not DCC-ready.






R1077 #2728

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