Pete172 Posted October 29, 2018 Share Posted October 29, 2018 Hi,My Railroad A4 Mallard, the model with a tender that used to house a ringfield motor in a previous design/ release ( R2784x) has sparks apprearing when the front bogey wheels touch the valve gear on a very tight point curve.I have removed the body and unplugged the decoder (Loksound) but left the motor wiring and wheel contacts in place and proceeded to test with my meter. I find continuity when I touch the driving wheels on both sides of the loco ! ..I thought the wheels on both sides should be insulated from each-other ?, but assuming the driving wheels are metal and the driving rods & linkages are screwed to the wheels ( the rod assembly is made of 1 metal part which bridges both sides for the loco) then I can't see how this arrangement could possibly avoid a direct short-circuit !..Any ideas on this would be much appreciated ..Pete. Link to comment Share on other sites More sharing options...
ronbram Posted October 30, 2018 Share Posted October 30, 2018 One can safely asume that the bogey wheels are isolated from the axle, but since the wheels are metal them selves, they will be live and will cause a short circuit if the valve gear is somhow electrically connected to the driving wheels. I would try to find or scavenge an old car for some plastic wheels that fit in the bogey. When that helps paint the wheels silver. Link to comment Share on other sites More sharing options...
Pete172 Posted October 30, 2018 Author Share Posted October 30, 2018 Hi thanks.I have investigated further , the wheels on the side wired to the black pickup wire, show continuity with the driving rods. The wheels on the other side (red pickup wire) have NO continuity to the driving rods.I don't understand how the wheel tyres can connect to the rods, so I guess it must be via the pickups ?I've got so many wires off now ( some have snapped at the solder points), I can see a major re-wire taking place to get it going again !! Thanks,Pete Link to comment Share on other sites More sharing options...
WilliamDavid Posted October 30, 2018 Share Posted October 30, 2018 A problem with older Hornby A3,A4 and probably other locos, is that one of the pickups conducts through the chassis to the motor.They corrected this design flaw in later models.I have modified all my affected locomotives. Link to comment Share on other sites More sharing options...
Pete172 Posted October 31, 2018 Author Share Posted October 31, 2018 Hi , I think I have solved it.I removed the pickup strip under the chassis and found that the plastic strip has a hole under one of the contacts ( the black wired one) that aligns with a dimple in the body, thus, when connected & screwed together the black wired pickup connects to the chassis via the hole & dimple design. I have now applied paint to insulate it, and so I now have an insulated chassis and driving rods, which can't short out on bends.This is a Hornby DCC (decoder fitted) model, so why they still use this design beats me ... I just can't see the need for a live chassis... ? - any thoughts on this ? Thanks,Pete Link to comment Share on other sites More sharing options...
96RAF Posted October 31, 2018 Share Posted October 31, 2018 MN uses the same methodology with the lower chassis holding one pickup set against a spigot on the chassis. The chassis connects using a screw tag lead to the DCC socket The other pickup is wired through a hole in the chassis block up to the DCC socket.Mine has been trouble from the start and I intend to replace the Hornby wipers with ESU coach lighting wheel wipers.Rob Link to comment Share on other sites More sharing options...
WilliamDavid Posted October 31, 2018 Share Posted October 31, 2018 If you have insulated the pickup from the chassis, you are now relying on the tender pickup for that side's supply.I removed the pip, soldered a wire to the pickup, and routed it along with the other pickup's wire. Link to comment Share on other sites More sharing options...
Pete172 Posted November 1, 2018 Author Share Posted November 1, 2018 Hi David, All.A few wires have now snapped off the underside of the decoder Socket, despite gentle handling, so I have had to go back to basics to re-solder the correct wire to the correct socket female pin ( I can;t find a circuit diagram for my DCC fitted Mallard R2784x anywhere - any suggestions ?Anyway, I have painted over the pip and also painted the hole in the strip, so no electrical connection now.I have led the tender pickup L/H wire and joined it to the loco L/H hand pickup wire, I then soldered them into what I think is the correct pin under the DCC socket. I did the same for the R/H side . I think this should provide electricity from both the tender and loco, on both sides.I think this should work, would you advise I should test it first on my DCC programming track ? ( The decoder is a Loksound V4 and I don't wan t to fry it ! ).Thanks for your help.Pete. Link to comment Share on other sites More sharing options...
jane1707819582 Posted November 1, 2018 Share Posted November 1, 2018 Hi David, All.A few wires have now snapped off the underside of the decoder Socket, despite gentle handling, so I have had to go back to basics to re-solder the correct wire to the correct socket female pin ( I can;t find a circuit diagram for my DCC fitted Mallard R2784x anywhere - any suggestions ?Anyway, I have painted over the pip and also painted the hole in the strip, so no electrical connection now.I have led the tender pickup L/H wire and joined it to the loco L/H hand pickup wire, I then soldered them into what I think is the correct pin under the DCC socket. I did the same for the R/H side . I think this should provide electricity from both the tender and loco, on both sides.I think this should work, would you advise I should test it first on my DCC programming track ? ( The decoder is a Loksound V4 and I don't wan t to fry it ! ).Thanks for your help.Pete.pin 8 red pin 4 blackpin 7 blue pin 3 greenpin 6 white pin 2 yellowpin 5 grey pin 1 orange so pickups to 8 and 4 motor from 5 and 1 Link to comment Share on other sites More sharing options...
96RAF Posted November 1, 2018 Share Posted November 1, 2018 Definitely put it on your programming track because if there is a wiring fault you will get an error and the low programming current will not be enough to cause damage. If you can reprogram an address or read back a CV value then you know all is well.Rob Link to comment Share on other sites More sharing options...
Rog RJ Posted November 1, 2018 Share Posted November 1, 2018 I wouldn't risk testing with a sound decoder even on the programming track.Do your initial testing with a much less expensive basic decoder. It hurts your pocket when you destroy an ordinary decoder but it hurts a whole lot more when you destroy an expensive sound decoder. Link to comment Share on other sites More sharing options...
Pete172 Posted November 2, 2018 Author Share Posted November 2, 2018 Thanks for your sound advice...I will try fitting a non-sound decoder before placing on my prog track.. Link to comment Share on other sites More sharing options...
Pete172 Posted November 6, 2018 Author Share Posted November 6, 2018 Hi all , just to conclude this topic, my Mallard is fine now, no shorting since I insulated the chassis & driving rods from the pickups ( as described earlier).Many thanks for all your help. Pete Link to comment Share on other sites More sharing options...
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