N gauge DCC decoder fitting notes

Transcription

1 November 2015 Andrew Roscoe i

2 Contents 1 Essential tools Random Top tips General procedure for 1970s-1980 s Graham Farish steam locos Take photos! Remove body... 6 Remove the upper brush clip, spring, brush, and brush holder Remove wire and (optionally) capacitor but not its lower lead! Experiment with a dead or dummy decoder to check installation position Remove wheels and valve gear Make chassis connection point Remove brushes Remove motor Prepare lower brush clip File chassis Black paint Re-install motor Install Digi-Hat, and reinstall lower brush, spring, and clip Check insulation (Optional) temporary grey wire Re-install upper brush holder, brush, spring, and clip (Optional) Last chance to run the motor at DC Insulate body Optionally, remove white and yellow leads from decoder Re-install wheels Stick decoder on Solder grey decoder wire to upper brush Solder decoder red wire to chassis (right wheel (and tender) pickup) Solder decoder black wire to left wheel (and tender) pickup Solder orange decoder wire Insulate and tape Check continuity and insulation Try programming track Try on main track (0.5A) Try on main track (3A) Refit body Examples of Farish conversions GWR Pannier Tank (4F), 1970 s model BR Prairie Tank, 1970 s model GWR Hall, 1970 s model LMS 8P, 1980 s model Stanier 8F, 1980 s model BR Class 08, 1980s model BR Class 37/47, models 8014 & Minitrix conversions Britannia 7P Standard 9F, Evening Star, DCC-ready locos Fowler 3F Jinty Ivatt 2MT Black MT Camelot WD Austerity B ii

3 1 Essential tools Here is the list of tools that I would consider essential: Soldering iron with the smallest bit you can get. I use a 0.4mm long round bit. Digital Multimeter (DMM) with resistance and/or continuity-test modes. Jewellers screwdrivers Needle tweezers Square needle file Small needle-nose pliers Wire strippers Scalpel, scissors. Kapton, or generic Polyimide insulating tape. I use 6mm widths and 12mm widths, but you can get others. I buy from Farnell/Onecall part #s and Some really small heatshrink for joining decoder wires. I got some General Electronics, Heat Shrink 2:1 1.6mm Clear from Coastal DCC and it seems to be ideal. If you can get it, some Kynar SK24 heat shrink 1:2, high temp, 2.4mm. This is identical to the heat-shrink sold in the Digi-Hat and you can cut new small lengths in case you make a mess of it the first time, or ever need to remove the original Digi-hat heatshrink and do it again. I use part CB00899 from CPC/Onecall/Farnell. Dremel tool with small grinding bits Alcohol for cleaning, and foam swabs etc. Really good desk lamp: these ones with the integral viewer/magnifier are great. Desk vice is occasionally useful. Very occasionally, hammer and punch! Vacuum cleaner with soft brush attachment 3

4 2 Random Top tips Here are top tips. In no particular order: 1. After checking isolation etc., on a brand new conversion always put it on the programming track first (which is current limited by your controller), and make sure you can communicate with the decoder and set its address before gently trying it on the main track. Either a problem short-circuit or open-circuit will simply be shown as an inability to communicate with the decoder, instead of (potentially) instant destruction. 2. Get a car tail-lamp bulb, and install it in series between your controller and your main layout feed. I have a three-way switch so I can choose between a. No resistance b. The brake filament in parallel with the tail-light filament. This limits current to about 3A. If there is a short the lamp will be bright but the Digitrax Zephyr (3A max) or higher capacity DCC sources will not trip out. You can run multiple locos in this setting, and it makes your layout tolerant to short-duration shorts when older locos with big flanges pass through points. If there is a sustained short, it will be obvious because the room is bathed in light, and its better feedback than seeing odd messages on your controller. c. Most usefully for tying new DCC conversions, you can switch it so just the taillight filament ONLY is in series. This limits current to about 0.5A max and pretty much guarantees that you can t destroy even a fragile CT decoder the first time you try your loco. It s too much resistance for running an older loco properly (it may not have enough torque to get up to full speed), but it s worth trying for the first few seconds, just too see if the motor is trying to turn properly, or if there is a short. Much better taking a few seconds to try that, than just seeing a puff of smoke from the decoder the first time you try to turn the wheels. Some of the modern locos may run fine even with the 0.5A limit. Go back to the 3A setting (both filaments in parallel) if it all looks good. 3. (Don t laugh!). Never try to clean your commutator with Track Magic, especially on an older 3-pole motor loco. This seemed like a good idea to me at the time (both times!), but I think it cost me 2 CT decoders. I think it is quite conductive, as well as an cleaning fluid, possibly even when it is dry. Only use alcohol on the commutator, and make sure it is absolutely clean and dry again before re-energising the loco. Make sure no gunk is wedged between the commutator poles. On the old Farish 3-pole motors, just a single spec of metal or a good wedge of carbon between 2 of the poles will cause a dead short between the armature connections and a CT decoder will be instantly fried. 4. If you do burn a CT decoder, don t bin it. Keep it with the wires on, and use it as a space model for your next conversion. You can experiment with it in the next loco, checking for positioning and space, and where all the bits of tape will go. If it gets mushed, it doesn t matter. When you re sure it s all going to fit and you worked out the wire run placement, install the new (working) decoder. 4

5 5. On the Farish GWR Hall and GWR Prairie locos, the gear is annoying as it falls apart as soon as you remove the body. It s very useful to be able to run the loco without the body so you can see what the commutator is doing (sparks, or hopefully not!). Also, it s nice not to have the piston rods flapping about the whole time you re trying to do the conversion. A solution to this is to make a nut for the bolt which normally screws into the chassis. I made one out of a small bit of margarine tub lid. Just melt a small hole with a soldering iron, and then self-tap the screw into it. Now you can use this as a nut which acts as a fake body to hold the slide-bars in place. Figure 2-1 : Nut / fake body to hold slide-bars on some locos. (GWR Prairie). 6. Don t solder the decoder orange wire direct to the lower brush clip on Farish locos. Instead, use a short length of orange wire to solder to the brush clip, and then join that to the orange wire from the decoder. There are several reasons a. You can try any number of times to get the neatest solder joint to the brush clip, without risk of damaging our decoder. b. You can check continuity (and hopefully lack of) between the lower brush clip and the chassis more easily than by probing the tiny pad on the decoder. c. You can run the motor with DC by using this wire. d. You can, if you need to, disconnect the lower brush from the engine by simply de-soldering the joint between the wire and the decoder wire, instead of having to de-solder from the brush clip, where the joint is covered by Digi-Hat heatshrink. 5

6 3 General procedure for 1970s-1980 s Graham Farish steam locos This chapter describes a generic procedure which I have been following. You can (and may need to) carry out some of the steps in slightly different orders to that given here, particularly if things don t go perfectly smoothly, but the order below is logical for most cases. 3.1 Take photos! First, take good photos of your loco before you start, from multiple angles. Make sure you get shots of the valve gear and coupling rods. Make sure you can identify which wheel belongs in which position and which way round, by identifying the small differences and imperfections which wheels normally show. That way, if you drop all the bits, you can still re-assemble them in the right order. 3.2 Remove body Locate the screw holding the body on (often towards the front of the loco), and carefully remove the body. Put all the bolts, nuts, etc. in a small lockable pot (I use an old 35mm film canister), inside another lockable tub (I use plastic takeaway tubs). Keep the tops on so if they ever get knocked over, you don t lose the bits in the carpet or down the skirting boards. 3.3 Remove the upper brush clip, spring, brush, and brush holder. Prize off the upper brush clip, spring, and brush. Now you can also remove the brass brush holder. Notice that it is usually not flush with the plastic motor chassis, but that the wire (see below) acts as a washer and separates the brush holder from the plastic motor chassis by a small amount. This sets the correct clearance between the brush holder and the commutator. When you re-assemble the whole thing later, you usually need to insert a washer of the same thickness to recreate this clearance. Figure 3-1 : Remove brush clip, spring, brush, and brass holder. LMS 8P. 3.4 Remove wire and (optionally) capacitor but not its lower 6

7 lead! Locate the wire between the bolt (connected to the left-hand wheels, normally), upper brush clip, and the upper lead of the suppression capacitor. Take a note of the routing this wire takes, it is a good clue as to where you will have space to route wires when you add the decoder. Some locos have space between the top of the motor and the body, but no space at the sides. Other locos have little or no space between the top of the motor and the body, but a bit more at the sides. Remove this wire, and keep it in your box! You might need it later, or if you decide to go back to DC operation. Figure 3-2 : Remove this wire (left wheel connection). LMS 8P. 3.5 Experiment with a dead or dummy decoder to check installation position Now is a good time to experiment with either an old blown decoder, or a space model of one made from balsa or an old bit of plastic. Tape it on where you think it might fit, and try reassembling the bodywork. See if it fits, and also account for where you think the wires will run. Work out where you will have a bit of space to store some extra loops of wire to allow for wires that are not cut so close to length that there is no margin for error. Figure 3-3 : Early experimenting to check space (Stanier 8F) So far, I never found a case where the CT DCX76Z decoder would not fit into the loco, and I never made severe modification of the body. The only body modifications I have done are to 7

8 machine away casting lugs from a couple of locos like the Pannier and Prairie tanks. Figure 3-4 : Examples of removing protruding casting lugs (GWR Pannier & GWR Prairie) 3.6 Remove wheels and valve gear Try to keep the valve gear, guides and wheels together as they come off the loco, and put them straight in their own closed tub so that later you can re-assemble all the wheels and gear back in exactly the same position order, handedness, etc., as it started. 3.7 Make chassis connection point In the end, you will still need a good electrical attachment to the chassis ground, and it is surprisingly difficult to make a new one. The chassis metal will not take solder, and there are few (if any) locations where you could drill/tap in a new screw attachment, even if you had the guts. I recommend you either leave the suppression capacitor there in its entirety (even though you will not reconnect anything to the upper leg), or you clip it off right next to the capacitor body, leaving the entire lower lead attached to the chassis where it is clamped in, so you can (later) solder the red decoder wire (right wheels) onto it. In the latest Digi-Hat instructions which came with my latest Digi-Hats, this is what they recommend now. If the original lead comes off the chassis, you can try and insert a new one, but finding a piece of wire exactly the right diameter can be difficult. If the wire has come out, is lost or loose, you can insert a new one and then you need to use a punch and a hammer to bash the chassis metal back around it to get it re-clamped. This is a scary process and you need to have everything striped off the chassis before attempting it. Best avoided if you can. This connection point to the chassis is a bit of a weak point. I have had at least one case where the wire came off and I had to insert a new one, using the hammer and punch technique. On my 8F, it all looked good right up until after the whole decoder was installed, with electrical contact resistance measuring apparently <0.1Ω from right-wheels to the wire, and <0.1Ω from the wire to the red pin on the decoder, but from that red decoder pin to the right wheels was open circuit and the decoder could not be programmed. Turns out, the wire was only making good electrical contact to the chassis when I was pushing it with the DMM probe. 8

9 In the long term, I d like to find a more reliable chassis connection method than this bit of capacitor lead wire stuck in the rear of the chassis, but for now this is the best I have done. Figure 3-5 : Leave capacitor, or snip lead at capacitor body so that (later) red decoder wire can be soldered to it. 3.8 Remove brushes Prize off the lower brush clip, and extract the lower brush, spring, and brass holder. Put all these bits in the small pot and close the lid! If your model has seen a lot of use, your brushes may look like these in Figure 3-6! In so, order yourself a new set (GF0111 from BRLines). 3.9 Remove motor Figure 3-6 : Brushes. Worn out (left) and new sets (right) The motor is attached to the chassis with a profiled slide in fit at the rear of most Farish steam locos (blue circle in Figure 3-7). At the front it is held down by the bolt and nut which carries the left-wheel current, which you removed already. So, gently push the motor up from the chassis at the front (red circled area in Figure 3-7), until you can then gently push it forward and it should slide off the chassis. Put it in the tub with the rest of the bits and put the top back on! 9

10 Figure 3-7 : Gently prize up at front (red circle) and then push motor forwards so it slides out from chassis (blue circle) You can clean the commutator and carry out various other maintenance if you choose. Don t clean the commutator with Track Magic though! 3.10 Prepare lower brush clip The lower brush clip, and the orange wire leading to/from it, needs to be totally insulated from the chassis, for the lifespan of the locomotive. If either this brush clip, or the orange wire conductor, ever comes in direct contact with either the chassis or wheel, the decoder will die. To achieve this, you need to first solder a wire onto it, and then shrink on the Kynar 2.4mm heat-shrink provided as part of the Digi-Hat kit (or if you bought a length yourself). The positioning of the wire is critical, especially for locos with big drivers like the 8P, Prairie, or Hall. The wire will only clear the wheels on those large-driver locos if you solder it exactly as shown, with a minimal amount of solder so that the entire join does not protrude out of the concave recess in the brush clip. It s worth checking your brush clip first. It s not clear from Figure 3-8 and Figure 3-9 but that particular brush clip turned out to be asymmetric, with one side longer than the other by about 1-1.5mm. It must have been made on a Friday afternoon in 1982 after a trip to a local Poole pub. I didn t notice it until after I d soldered it and shrunk the Kynar on, when it just wouldn t fit neatly back on as it was so asymmetric. I had to rip it apart and put that particular brush clip back as the TOP clip (where it shape doesn t matter so much), and swap the original top clip (which fortunately WAS symmetrical) down to the bottom clip duty, soldering the orange wire onto it instead and using new lengths of Kynar. This is another reason to get more stock of Kynar than DCC Supplies send you with the Digi-Hat. You often need more than one go to get it just right. Almost always, the lower brush clip will connect to the decoder Orange wire. Get or cut a short length (2-3cm) of orange wire (not connected to the decoder, but a free bit). Strip just 1mm, and tin the end with solder. Clip it back to 1.5mm (maximum) stripped if the insulation shrinks back when you tin it. Now, solder it on to the brush clip so that he tinned end sits within the concave recessed groove in the brush clip. Don t use too much solder and re-do it if either the wire or the solder projects out of the concave groove at all. Also, the wire must be able to bend at the end of the groove so that it takes a sharp 90 degree bend upwards so it can get out from the heat-shrink which will wrap right around the brush clip. 10

11 Figure 3-8 : Soldering on a length of orange wire Then get the two Kynar heat-shrink lengths and slide them over the brush clip. It is a tight fit, especially over the side with the orange wire where it will take the 90 degree bend. Figure 3-9 : Bend the orange wire 90 degrees and slide on heatshrink Shrink it on. You need it properly shrunk so it is really snug. I tried using the soldering iron passed close by, but it s hard to get it really shrunk on. I find a better result by putting on a head-torch and very carefully lowering it down (holding the orange wire) towards a gas hob flame on the lowest setting. It is very sensitive nothing can happen for ages and then suddenly it shrinks very quickly and you have to be careful not to melt the whole thing. This is where it s nice if you ve got your own Kynar heat-shrink because if it goes wrong you can just cut some more and try again. Check it with a magnifier and make sure the heat-shrink didn t puncture or split, especially at the sharp corners at the top of the brush clip. Officially that s it with the brush clip. Personally, I do 2 more stages. Firstly, I squeeze the two sides together just a tiny bit. This is to try and get it the most snug fit on the chassis possible, because the clip is now wider than it was, due to the heat-shrink thickness. 11

12 Secondly, I clean the remaining exposed bit of the clip with alcohol, and then cut a tiny bit of Kapton tape and stick it on the lower side of the brush clip, and also wrap it around the edges so that it comes part-way onto the spring-contacting side. This helps to minimise the (small but finite) risk of the bottom edges (which have no heat-shrink) touching the chassis at all, or contact being made by brush carbon facilitating such a contact. If the tape looks like it has covered the central circular area on the inside, where the brush spring is going to contact, then cut it back a bit with a scalpel. Figure 3-10 : Lower brush clip with wire, heat-shrink, and Kapton tape 3.11 File chassis The next job is to file the chassis down. This is required because the brush clip is now quite a bit thicker than it was. If you don t file the chassis, the sides will stick out and likely foul the wheels. If the wheels wear through the heat-shrink and contact the clip, a small decoder like the CT DCX76Z will be fried instantly. The Digi-Hat instructions suggest this filing is occasionally necessary. I would say it s essential on all big-driver locos, and useful for all steam locos. You can minimise the filing on a steam loco with small wheels like the 8F and 0-6-0s, the class 08, and on big diesels its irrelevant. It is difficult to describe how much to file the chassis. One way of judging it is to take the brush clip you didn t modify, and try it on the chassis. If it is quite a loose fit and wobbles about quite a bit, you probably took enough off. Also, try the new brush holder with the heat-shrink. Ideally it will fit on as a snug fit, and the outside will be really quite close to being flush with the chassis sides (Look forward to Figure 3-13 for an example). I also take a little bit off the rear and front vertical edges of the chassis where the brush clip goes in. This is to allow for the heat-shrink which made the clip bigger, and also to minimise the risk of the bottom edges of the brush clip (hopefully insulated with kapton tape), contacting the chassis. Be careful not to take material off the thin bits of chassis supporting the rear drivingwheel axle, or to bend or damage those thin parts. Round off the edges, in particular at the top side, to allow for the profile of the brush clip, and minimise the risk of tearing the heat-shrink when you slide the brush clip on. The aim is to let the brush clip slot in with the lowest profile possible, so the outside of the brush clip comes as flush with the chassis as you can, without sticking out. Something like Figure Clean off all the swarf with alcohol/swap, blowing, etc. When you finish, it looks something like this: 12

13 3.12 Black paint Figure 3-11 : Chassis filed down I have a non-standard step here. I apply some black gloss humbrol enamel paint to the top and bottom of the chassis, around the brush hole (top and bottom) and on the vertical parts of the chassis. I think this minimises the chance of electrical contact between the brush clip and chassis, and also between the brush itself and the chassis, if carbon deposits build up. Either could fry your decoder. I find there is not much point painting the sides of the chassis you just filed, since it rubs off when you slide on the brush clip, and you want a low profile there anyway. The heatshrink insulation is quite effective on those parts anyway. If paint spills on the filed sides, don t worry. It may come off when you put the brush clip on, or you can file it off again, or just leave it, unless it is a big thick blob. By the way, there is a possibility that some gloss black paint is made with carbon black dye which may be conductive. I tested mine with a DMM and found it to be totally non-conductive, so I suppose it must use a magnetite-based pigment or something. 13

14 Figure 3-12 : Chassis painted around brush holes, top and bottom 3.13 Re-install motor Now you can re-install the motor. It s the reverse process to section 3.9. If it seems reluctant to slide back in, don t force, but ensure the rear motor bearing (white plastic) is aligned with the plastic motor chassis. If this has started sliding out the motor chassis it can stop the motor wanting to slide back onto the chassis, until you push the bearing back into position Install Digi-Hat, and reinstall lower brush, spring, and clip Now you can install the Digi-Hat. Most of mine are slightly asymmetric so I try to insert them so that the hole is symmetric about the chassis centreline, and the hole position for-and-aft is favourable for a near-central commutator alignment. Re-install the original (or new) brush. If you can, re-align the worn concave brush shape with the commutator. This is tricky to do deliberately as it is so fiddly and hard to manipulate, even with tiny tweezers, but one approach is just to keep starting again until eventually one time you drop it into the holder, it looks just right against the commutator. Now install the the spring, and finally the clip, complete with orange wire, heat-shrink, and Kapton tape. If you did the chassis filing well, then the final assembly at this point will show that the brush clip hardly protrudes from being flush with the chassis sides (Figure

15 Figure 3-13 : Motor and lower brush/holder/spring/clip installed, flush with chassis sides (GWR Prairie 2-6-2). (The overflowed black paint on the chassis bottom was cleaned off after this photo, to ensure the chassis bottom was properly flat again). Sometimes I need to repeat the above process a few times until I m happy. If you end up doing this, check the Kynar heat-shrink each time to make sure it didn t rip, tear or puncture when you manipulated it onto the chassis, especially if you left any sharp bits of chassis after filing, or it is a very tight fit Check insulation Check the continuity (and hopefully lack of) between the end of the orange lead, and the chassis. It should reliably read open-circuit. If you see any sign of continuity, check the Digi-Hat, brush clip, etc. and try to work out where the connection is being made, and fix it (Optional) temporary grey wire At this point, you have the final opportunity to run the motor under DC. This can be useful if you replaced the brushes, cleaned the commutator a lot, or you just want to make sure it runs after re-assembly. You can solder a spare (ideally grey) wire onto the top brush holder, and then in 2 steps time you will be able to run the motor under DC. If you don t need to run the motor under DC, just skip this step Re-install upper brush holder, brush, spring, and clip Before you re-install the upper brush holder, remember that it used to be separated from the plastic motor chassis by one thickness of thin wire (section 3.3). Search around for some wire the same thickness as that original wire (leads from small components like 1/8 th Watt resistors might do), or, chop a bit off that original wire. Make a little washer (Figure 3-14) and then try the brush holder in place (the original brass one). Visually check the clearance between the brush holder and the commutator. If its touching the commutator, that s too close! Compare it to the Digi-Hat installation or photos of the original. In one instance (Stanier 8F) I decided the extra clearance wasn t required and removed the washer. Figure 3-14 : Washer for upper brass brush holder. 15

16 Then, install the brush (old or new) suitably aligned, and spring (Optional) Last chance to run the motor at DC If you elected to solder a grey wire to the clip, you can now test-run the motor at DC if you like. Connect your 0-12V DC controller to the orange and grey wires using crocodile clips or similar, and run the motor. Once this is done, you can remove the upper brush clip again, and de-solder the temporary grey wire from it. Figure 3-15 : Optionally you can run the motor at DC (here the wheels have not been installed yet) Insulate body Wherever there is the chance of the decoder contacting the metal body, coat the inside of the metal body with Kapton tape. It is quite fiddly and tends to stick to tweezers, fingers, and everything except what you want it to stick to. But, once you get it in place and smoothed down, it does stick quite well. Use alcohol to clean the surfaces first. On some locos with complex bodies it takes quite a while to get all the surfaces covered, and you may need to make careful cuts in the tape to get it to fold over the bends and angles inside the body. So far, the Stanier 8F was the hardest shape I came across, but still quite do-able with an hour or so and some good music. 16

17 Figure 3-16 : Coat the inside of the body where the decoder might touch, with Kapton tape. (Stanier 8F) Optionally, remove white and yellow leads from decoder In some locos, there isn t much space, and you aren t going to do anything with the white and yellow decoder outputs (front and rear lights). In this case, you can make life a bit easier by desoldering the leads completely from the decoder. This is an irreversible process, unless you are very good at soldering, since the pitch of the decoder pads is so fine. Even if you re sure about doing this, you need to do the de-soldering under a magnifier and with a very steady hand. If you touch the black lead with your iron and de-solder it accidentally, or bridge the gap to the black lead with solder, it s going to be fiddly to put right. If you don t want to risk it, another option is to cut the white and yellow leads quite short, slightly different lengths, and seal them with heat-shrink so the cores can t touch each other or anything else. This is lower risk but you have to find room to stow the wires Re-install wheels Re-install the wheels, adding small amounts of oil to the axles at your pleasure. Hold them on with the bottom-plate using one or more of the screws into the chassis, and re-assemble the valve gear. Use patience and tweezers, etc., and some suitable music to keep you calm (perhaps also a gin and tonic with plenty of lime and ice). Loosely add the long screw and nut which carries the current from the left-hand wheels up to the top-front of the plastic motor chassis. Have a small celebration if you manage to re-assemble it all so it looks just like the original photograph, and nothing is broken Stick decoder on Stick the decoder onto the loco with Kapton tape, by using the wire harness neatly as an anchor. I try to avoid taping the decoder directly, as the CT instructions suggest the chip needs clear access for airflow to dissipate heat. 17

18 Figure 3-17 : Sticking the decoder on. (GWR Prairie). At this point the wires are flapping all over the place and you need to be careful not to pull them off the decoder accidentally, or get frustrated with anything. It is nice at this point to try the body on to make sure it s going to fit. But, with all the wires flapping around, this can be very hard or impossible. This is why the step 3.5 is so useful to do early. If you did a really good job in step 3.5, then you ll have a really good idea and high confidence that it s going to fit, and know how you are going to route the wires Solder grey decoder wire to upper brush Cut the grey decoder wire to length and solder it to the upper brush clip. Don t make it as short as possible, try to give enough slack to allow for mistakes, and possible relocation of the decoder later to a different locomotive. You can lose a certain amount of slack in tidy loops of wire which can be held in place neatly using Kapton tape. This appies to the red, black and orange wires too Solder decoder red wire to chassis (right wheel (and tender) pickup) Cut the red decoder wire to length and solder it to the tail of the old suppression capacitor which is hopefully still electrically connected to the chassis. If you have a tender with pickups, and it has a wire for the right hand wheel pickups, this also connects to the same chassis point Solder decoder black wire to left wheel (and tender) pickup Cut a small length of wire (e.g. an old resistor lead offcut), and bend it around the long screw which goes through the chassis from the bottom to the small nut at the top-front of the motor. You want a loop around the screw, and a small extra tail that you can solder on to. Normally its easiest to remove the screw, bend the wire around and shape the tail, and then re-install the long screw and nut. Cut the black decoder wire to length, and solder it to the small tail, using minimum time so you don t melt the black plastic. If you have a tender with a wire to the left-wheel pickups (this is normal), then this also solders to the same point. 18

19 You could try and minimise the risk of melting the plastic by soldering to the wire before installing on the screw, but this could be very fiddly. Figure 3-18 : Installing black wires for left-wheel pickups Solder orange decoder wire The final connection is the orange decoder wire, which is cut to length and then soldered to the orange wire connected to the lower brush clip. Remember to slide on a short length of heatshrink so that after you join the two orange wires, you insulate the join. Shrink it using the soldering iron bit held close. Try not to melt any insulation off other wires, or to melt anything 3.27 Insulate and tape Tie all the loose wires down with Kapton tape, in routes that should not foul the re-assembly of the body. Add Kapton tape to make sure the decoder cannot touch anything conductive. In particular, make sure the decoder cannot touch screw or nut which carries the the left-wheel pickup (Figure 3-18). Normally, add tape which covers this nut completely Check continuity and insulation At this point you can do a final check for continuity and insulation, if you have a small enough probe tip on your DMM that you can safely touch the decoder pads without causing damage. If you did all the previous steps properly, or you don t want to risk damaging the decoder by probing it with unsteady hands or big probes, you can skip this step Try programming track Try the loco on the programming track and make sure you can program the decoder Try on main track (0.5A) Try the loco on the main track, with a 0.5A maximum current limit using the car tail-lamp with only the tail (not brake) filament in series. See if the loco wants to go backwards and forwards slowly. If it seems sluggish, this may be due to the resistance of the tail lamp. Watch for any dubious signs of problems on the commutator. Stop if anything looks weird Try on main track (3A) Switch to a 3A maximum current, i.e. the tail-lamp filament in parallel with the brake-light filament. Try the loco forwards and backwards slowly again. Watch for any dubious signs of problems on the commutator. Stop if anything looks weird. 19

20 If everything looks good, gradually increase speed, etc Refit body Refit the body and then repeat steps 3.29 to Of course, if you find the body doesn t fit, you may need to reposition wires and go back around a few steps.. If all is well, that s it. Cosmetically, you can paint sections of the wires black if the coloured wires are visible in the cab or a tender or tank loco, and they annoy you. 20

21 4 Examples of Farish conversions These are examples of the actual conversions, with some very informal notes. 4.1 GWR Pannier Tank (4F), 1970 s model 1104 Figure 4-1 : 9400 Tank, original condition The chassis is connected to the starboard (right hand) wheelset, and that was connected to the lower motor brush. The left hand (port) wheelset comes up through the insulated plastic, black wire, and to the top motor brush. This is the conventional arrangement. So, the decoder ORANGE (motor right/+) wire should go to the lower brush with the Digi- Hat. The decoder GREY (motor left/-) wire should go to the top brush. Chassis (right hand wheels) should go to decoder red. Left hand wheels (through the bolt to top of plastic) should go to decoder black. A small amount of machining, using a dremel, was done to remove the casting lugs on the inside of the body. 21

22 Figure 4-2 : 9400 Tank, DCC conversion 22

23 4.2 BR Prairie Tank, 1970 s model 1605 Figure 4-3 : 6100 Prairie Tank, original condition 23

24 Figure 4-4 : 6100 Prairie Tank, DCC conversion 24

25 4.3 GWR Hall, 1970 s model 1404 Figure 4-5 : GWR Hall, original condition On this loco, I also installed the tender pickups from BR Lines. On this particular loco, there is almost no space between the top of the motor assembly and he body. The wires have to go around the side. Also be careful to insulate the top brush clip to be absolutely sure it can t touch the body. Figure 4-6 : GWR Hall DCC conversion 25

26 4.4 LMS 8P, 1980 s model 1811 Figure 4-7 :LMS 8P, original condition This loco is an example of one with really big drivers, and the lower brush clip needs to be really flush with the chassis. Keep filing the chassis until it s a really snug fit. 26

27 Figure 4-8 : LMS 8P, DCC conversion 27

28 4.5 Stanier 8F, 1980 s model 1905 Figure 4-9 :Stanier 8F, original condition The 8F has a quite detailed profile on the inside of the body, and wires cannot be run anywhere except the top, right in the middle. There is no space down the sides of the motor. The chassis extracts from the body at the rear first, which is unusual. Jiggle gently and it will come apart, but it is a bit fiddly. 28

29 Figure 4-10 : Stanier 8F, DCC conversion 29

30 4.6 BR Class 08, 1980s model 1005 Figure 4-11 : Class 08, original condition Note, this model has the opposite rail/chassis connections to most Farish models because the commutator is at the FRONT of the model, and the worm drive is towards the cab. i.e., the motor is 180 degrees rotated from a normal steamer. The chassis is connected to the port (left hand) wheelset, and that was connected to the lower motor brush. The right hand (starboard) wheelset comes up through the insulated plastic, wire, and to the top motor brush. So, the decoder ORANGE (motor right/+) wire should go to the upper brush The decoder GREY (motor left/-) wire should go to the bottom brush with the Digi-Hat. Chassis (left hand wheels) should go to decoder black. Right hand wheels (through the bolt to top of plastic) should go to decoder red. Figure 4-12 : Class 08, DCC conversion 30

31 4.7 BR Class 37/47, models 8014 & 8004 These locos are identical inside. Figure 4-13 : Class 37/47, original condition Converting these locos is fairly easy, since you probably don t need to file the chassis at all, and the brush clip can stick out at the sides without causing any problems. Just check that the bottom of the brush clip, which isn t insulated with heat-shrink isn t touching the chassis at all (it comes very close, and the Kapton tape can be used to add some extra margin of safety). You don t need to be so careful soldering the orange wire on, and in fact it s better to take it out in a straight line vertical through the convenient hole in the chassis. Also check that the TOP of the brush clip is not contacting the chassis, because it comes very close. In fact, in my case the top of the brush clip (covered in heat-shrink) is butted solid against the chassis in one or two spots. A longer-than-normal section of Kynar heat-shrink can be useful here to make sure the heat-shrink really covers the top ends of the brush clip. 31

32 Figure 4-14 : Class 37/47, DCC conversion There is plenty of easy space above the chassis, and below the curved top of the body. You get to use the white and yellow wires too, for the lights! 32

33 5 Minitrix conversions These are great engines. Really robust. Also, relatively easy to convert to DCC, because the motors already have contacts which are insulated from the chassis (and hence left and right wheelsets). My approach was to make a pad/holder/insulator for the DCX76Z decoder to sit on. The pad is made from a small piece of microwaveable plastic container from a chinese takeaway. Its robust and can stand a good bit of heat. The decoder is held to it with fishing line, so that airflow is not impeded and the decoder can cool itself. 5.1 Britannia 7P /5/15 DCC installation with DCX76z. Removed suppression capacitor (it was destroyed and I could not read the value). The capacitor was across the supplies from the left and right rails. Also there were 2 small choke inductors: one between each end of the capacitor and the motor terminals. A problem was encountered because the little PCB connection to the chassis (for the left main driver pickup, and front bogie left wheel, and pony left wheel), did not (or was intermittent) in its connection to the actual chassis. No amount of soldering between the via/pad and the chassis metal would fix it reliably. So, during the installation there is an extra cream wire installed, which connects the chassis pad to the chassis through the screw which holds the valve-gear on. DCC Wiring: DCX76z Red DCX76z Black DCX76z Orange DCX76z Grey DCX76z White DCX76z Yellow Cream Cream Brown Right rail - to 2 driver copper spring contacts and tender (cream) Left rail -to chassis (left drivers, front bogie, pony) and tender (brown). Also return path for front lamp. Motor, top terminal Motor, bottom terminal Front lamp pin (returns via chassis, i.e. Black) NC Connection from chassis via/pad to actual chassis (screw) for better contact Right wheel tender connection Left wheel lender connection 33

34 Figure 5-1 : Minitrix Britannia DCC installation 34

35 5.2 Standard 9F, Evening Star, _Workhorses&P=93Evening_Star&H=00Introduction.shtml&X=36&R=1 The left wheels were connected to the green wire, and to the bottom of the motor. The chassis is also connected to the left side. It was through a tab on the bottom of the motor, but this had to be insulated during the DCC conversion. The left wheels of the tender are connected to the chassis through the tender coupling. The left front pony wheel is also connected to the chassis. The lamp outer is connected to the chassis. The right wheels were connected to the top connection on the motor through a red wire. The tender right wheels are connected through the black wire to the right side. The right wheels also connected to the lamp pin. The filter inductor was between the right-hand pickups (main and tender) and the red wire, in series with the motor. The filter capacitor was between the green wire (chassis, left wheels) and the top motor connection (red wire where it picked up the inductor too). DCC Wiring: DCX76z Red DCX76z Black DCX76z Orange DCX76z Grey DCX76z White DCX76z Yellow Right rail - to right driver copper spring contacts and tender (black wire) Left rail -to left driver copper spring contacts and chassis (front bogie, pony) and tender (via coupling). Also return path for front lamp. Motor, top terminal Motor, bottom terminal Front lamp pin (returns via chassis, i.e. Black) NC 35

36 Figure 5-2 : 9F in original DC condition, with suppression capacitor and choke 36

37 37

38 Figure 5-3 : 9F DCC conversion 38

39 6 DCC-ready locos 6.1 Fowler 3F Jinty The CT DCX77 will fit in this loco Figure 6-1 : Fowler 3F Jinty with blanking PCB Figure 6-2 : Fowler 3F Jinty with CT DCX77 39

40 6.2 Ivatt 2MT Note. To lift the tender body off its chassis, turn upside-down and carefully put a small screwdriver in a small gap (if you can find it!) and lever. It should shift. There are 4 tiny dimples/domes which engage to hold it in place that you have to release (one side at a time, probably). The NEM651 PIN 1 is on the PORT (left) side of the loco/tender. It is NOT on the right hand side, which is indicated on the service sheet. I also have a slab of lead in the cab for extra traction! Figure 6-3 : Ivatt 2MT with blanking PCB Figure 6-4 : Ivatt 2MT with CT DCX76D/N decoder installed 40

41 6.3 Black 5 Figure 6-5 : Black 5 with blank PCB installed Figure 6-6 : Black 5 with Digitrax CT DCX76N decoder installed I placed insulating tape on top of the motor in case the decoder contacts it. 41

42 6.4 5MT Camelot Tender body comes off by 2 small screws underneath at rear of tender. The NEM651 PIN 1 is on the STARBOARD (right) side of the loco/tender. Figure 6-7 : Standard 5MT with Digitrax DZ126IN decoder (correct orientation) ready to replace blanking PCB Figure 6-8 : 5MT with Digitrax CT DCX76N decoder installed I placed insulating tape on top of the metal tender weight in case the decoder contacts it. 42

43 6.5 WD Austerity Figure 6-9 : 5MT with blanking PCB installed I placed insulating tape on top of the metal tender weight when the decoder was installed, in case the decoder contacts it.. 43

44 6.6 B1 Figure 6-10 : B1 with blanking PCB installed Figure 6-11 : 5MT with Digitrax CT DCX76N decoder installed I placed insulating tape on top of the metal motor casing in case the decoder contacts it. 44