Bachmann 4MT tank-erratic running.

Discussion in 'Bachmann RTR' started by Keith M, Sep 23, 2016.

  1. Keith M

    Keith M Staff Member Moderator

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    I've been considering buying one of these for a while now, and Bachmann have just released a new incarnation of this model in the last week or so. I'd opted for Hattons to email me when they were available, but a few days before I got the email, I spotted on Ebay a seller with several new unused loco's for sale as a result of a layout that never got built. One of these loco's was the previous incarnation of said 4MT tank, DCC ready, and, to cut a long story short, I won it for a mere £63 (Hattons price for the new one is £111), and it certainly was brand new and unused, so I duly gave it a good 'running-in' session, but even after an hour or more in each direction, checking, polishing and resetting the pickups and wheel backs, relubricating, cleaning my track and rolling road, it's still an erratic runner, whether on DC or DCC (I've tried both!).The pickups are only on the 6 driving wheels, so I'm considering adding pickups to the 2 pairs of trailing bogie wheels, which shouldn't be too much of a problem and may help, but I was wondering if any other members have experienced problems with this particular model. It's too nice a model at too good a price to consider returning it to the seller, and return under warranty isn't an option as it's well out of warranty time, so.......any ideas/suggestions fella's???
    :confused: Keith.
     
  2. SRman

    SRman Full Member

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    To eliminate various possibilities, I would suggest all testing to be done on DC with no decoder installed.

    Can you supply electricity directly to the brushes? If so, is the running erratic? If it is, it suggests either gummed up brushes or something mechanical.

    If the running is NOT erratic with the brushes directly supplied, then the chances are it's poor pickups: poor contact withe the wheels, or loose or dry soldered wiring.

    Poor pickups could be caused by them not being sufficiently sprung to reach the wheel backs when the wheels are pushed to the extremes of their sideways travel: the cure is to bend the pickups slightly outwards. Poor pickups could also be caused by dirt or tarnishing, on the pickups or on the wheel treads/wheel backs.

    Bachmann tend to use coiled 'chokes' on their PCBs in the line to the brushes. These can be bypassed with wire to improve electrical reliability (at risk of causing some electrical interference on DC - a DCC decoder will have the suppression circuits built in).

    If the running is still erratic when the brushes are directly supplied with power, you may have to dismantle the gear train and clean and oil them all, while also checking to see if there are any split gears or missing or chipped teeth.

    These may well be things you have already tried, but they are worth posting in case anyone else has similar problems.
     
  3. Keith M

    Keith M Staff Member Moderator

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    Hi Jeff.
    I was beginning to think it might be a quartering issue causing the erratic running, but decided to cut the small PCB out and connect pickups directly to the motor, which has now solved the problem, so it must have been something on that PCB which was causing the problem. I intended removing the PCB anyway to create as much space as possible, as this loco may well be my next candidate for sound fitting (Zimo MX649R will go in boiler nicely although speaker will likely have to be a 'sugarcube' as it seems 'coal' and bunker are moulded as one, so not removeable!). Thanks for your advice, every days a school day, isn't it?:avatar:

    Keith.
     
  4. paul_l

    paul_l Staff Member Administrator

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    May also be a good candidate for a stay alive as well, put that in the bunker and the speaker in the smokebox / boiler area. And if you feel like it additional pickups on the bogie.

    My 4MT is a little irratic - not as bad as my Bachmann B1.

    I have a sound chip (actually had it for a few years now) for the B1 and currently has a DCC Concepts decoder with stay alive and still runs like a dog. So that one will get tender pickups, and place the decoder and speaker in the tender.

    Paul
     
  5. Keith M

    Keith M Staff Member Moderator

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    I have now got around to fitting sound to this loco, and boy was it a tight fit! Unfortunately it was so intensive 'shoehorning' it all in that I didn't have time to take photos. I removed the decoder socket as previously noted, filing the two small bosses under the socket flat to create maximum space for a 7mm tall round topped 'sugar cube' speaker below the chimney, and drilling out the chimney inside diameter through into the boiler to allow sound out. I prefer where possible for sound to come from the loco, and I was unable to get into the bunker area as an alternative anyway. It was possible (just) to fit the Zimo MX649 decoder on its edge between the motor and speaker, but wiring had to be kept as short as possible as it really is a very tight fit to reassemble the body back onto the loco, and I removed all unneeded wiring from the decoder, leaving only pickup, motor and speaker wiring. Upon testing, all was well and the loco runs perfectly on DCC, I just need to fix some real coal over Bachmann's moulded "coal", and some weathering to complete.
    Keith.
     

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