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Discussion Starter · #1 ·
Hi All and hope everyone is well. As a 'newbie' (or, more accurately, a 'returner') I'd very much appreciate any and all advice on hard-wiring a Hornby J36 TTS decoder to a nice old (1975) Airfix 2-6-2 GWR 6100 class side tank steam loco (Prairie) with no DCC socket. I am foxed by: 1) there being two red wires; 2) whether I need to go further than showing chassis/engine and remove main drive wheels to make this possible; 3) how to wire to the copper/plastic pieces behind the middle drive wheels. Any and all thoughts welcome! Some images attached. Thanks, All.
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Service sheet - https://www.lendonsmodelshop.co.uk/pdf/Airfix Locomotive Service Sheets/Prairie Tank.pdf
The driving wheels are plastic centered so current pick-up is by wipers on the back of them which are linked toether on the inside the plastic baseplate. The service sheet however only shows one wire from that baseplate so really you need a multimeter or something else to check the circuits; looking at it your photos it would seem that their are two wires from the baseplate to the motor but you need to find out if the metal chassis is live to the pick ups and or motor,
 

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The most important thing when installing a DCC decoder is to ensure that you completely isolate the motor from the wheel pickups, elsewise you'll fry your decoder.

Whilst I'm not familiar with this particular locomotive, one of the key things to check when fitting a decoder to older locomotives is that they have sufficient capacity to cope with the stall current of the motor. I notice that TTS decoders are listed as 800mA continuous/1A peak. Based on some motors I have of similar age these draw ~1.5A when stalled, which would again fry the decoder...!

Do you have a multimeter available? - You would be able to use this to both measure whether there is any continuity between the motor and pickups, and also the stall current of the motor @12V.

Regards,

Cameron.
 

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No way is the TTS decoder suitable, only 0.5A output rating, this motor will cook it, especially if you want to run the sound as well.

You really need to dismantle the mechanism rather more to get simple access to the pick ups and the motor brush contacts, and fully remove all the existing wiring, which includes the orange blob capacitor which is not required, a DCC decoder takes care of suppression.

These are among the simplest older models to hardwire, with the original wiring all removed solder the black and red decoder wires one each to a pick up strip, orange and grey one each to a motor brush, and you are done as far as motor power installation is concerned. Then use the programme track to check a correct installation by making a successful address change. Don't put the loco on track power until an address change has been made.

The motor is a goodun, I have a couple of these on DCC in N2 chassis, same Airfix GMR motor design. But it does have a high stall current, mine have 1.8A peak capable Lenz Golds in them (which probably gives a clue to how long ago they were converted to DCC, and still running successfully if noisily; the motor is a copy of the old MW005 which is near bombproof, but unless you got very lucky tend to make coffee grinder noises which doesn't in any way impair their running).

Oh and soldering the red and black wires onto the pick up strips, if it is like the N2 and has a plastic chassis, you need to be quick to avoid melting and smoke. Place the joints as far as possible from the plastic 'studs' that hold the pick up strips in place.
 

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Discussion Starter · #5 ·
Service sheet - https://www.lendonsmodelshop.co.uk/pdf/Airfix Locomotive Service Sheets/Prairie Tank.pdf
The driving wheels are plastic centered so current pick-up is by wipers on the back of them which are linked toether on the inside the plastic baseplate. The service sheet however only shows one wire from that baseplate so really you need a multimeter or something else to check the circuits; looking at it your photos it would seem that their are two wires from the baseplate to the motor but you need to find out if the metal chassis is live to the pick ups and or motor,
really helpful - thank you.
 

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Discussion Starter · #6 ·
The most important thing when installing a DCC decoder is to ensure that you completely isolate the motor from the wheel pickups, elsewise you'll fry your decoder.

Whilst I'm not familiar with this particular locomotive, one of the key things to check when fitting a decoder to older locomotives is that they have sufficient capacity to cope with the stall current of the motor. I notice that TTS decoders are listed as 800mA continuous/1A peak. Based on some motors I have of similar age these draw ~1.5A when stalled, which would again fry the decoder...!

Do you have a multimeter available? - You would be able to use this to both measure whether there is any continuity between the motor and pickups, and also the stall current of the motor @12V.

Regards,

Cameron.
Thanks so much for this. Really appreciated.
 

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Discussion Starter · #7 ·
No way is the TTS decoder suitable, only 0.5A output rating, this motor will cook it, especially if you want to run the sound as well.

You really need to dismantle the mechanism rather more to get simple access to the pick ups and the motor brush contacts, and fully remove all the existing wiring, which includes the orange blob capacitor which is not required, a DCC decoder takes care of suppression.

These are among the simplest older models to hardwire, with the original wiring all removed solder the black and red decoder wires one each to a pick up strip, orange and grey one each to a motor brush, and you are done as far as motor power installation is concerned. Then use the programme track to check a correct installation by making a successful address change. Don't put the loco on track power until an address change has been made.

The motor is a goodun, I have a couple of these on DCC in N2 chassis, same Airfix GMR motor design. But it does have a high stall current, mine have 1.8A peak capable Lenz Golds in them (which probably gives a clue to how long ago they were converted to DCC, and still running successfully if noisily; the motor is a copy of the old MW005 which is near bombproof, but unless you got very lucky tend to make coffee grinder noises which doesn't in any way impair their running).

Oh and soldering the red and black wires onto the pick up strips, if it is like the N2 and has a plastic chassis, you need to be quick to avoid melting and smoke. Place the joints as far as possible from the plastic 'studs' that hold the pick up strips in place.
Wow! Thank you so much for all this information. Yes, intimidated by the challenge, but ALSO yes because I feel better equipped and you have explained things so clearly I'm going to have a go. WITH a meter! Thanks again.
 

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Service sheet - https://www.lendonsmodelshop.co.uk/pdf/Airfix Locomotive Service Sheets/Prairie Tank.pdf
The driving wheels are plastic centered so current pick-up is by wipers on the back of them which are linked toether on the inside the plastic baseplate. The service sheet however only shows one wire from that baseplate so really you need a multimeter or something else to check the circuits; looking at it your photos it would seem that their are two wires from the baseplate to the motor but you need to find out if the metal chassis is live to the pick ups and or motor,
I was recently fiddling with one of these myself.
There are indeed pickups on both sides, however, inside the keeper plate, one side of the pickups is connected to the wire you mention. The other side has a tab which rests against the chassis block, meaning that the chassis block is live.
This may be an issue with the motor in that it too may not be insulated from the chassis, meaning that you can't isolate the motor for a decoder to sit between it and the pickups.
I will double check.
In the end, I actually replaced the chassis on mine with the Hornby version of the same thing (the version prior to the latest 'hi spec' version).
 
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