Marklin Koploper 37421

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Marklin Koploper 37421 - Circuit board/platine

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johnmarklin		#1 Posted : 03 September 2025 13:32:51(UTC) Retweet
Joined: 31/03/2011(UTC) Posts: 173 Location: Ireland		Hi fellow Marklin fans, I hope somone of you will be able to help me. Recently I bought an as new /not working Marklin Koploper 37421. I dismantled the motor unit and discovered that the previous owner had done some work on the driving unit. some wires were disconnected, the motor was disconnected and the solder tabs on the platine for the motor were damaged. I checked the decoder using an ESU decoder tester. Fortunately it is working perfectly and it is recognised by my CS3 when I connect the decoder tester to my CS3. However when I put the decoder into the Koploper motor unit and put it on the track it is not being recognised by my CS3. I suspect there is a wiring issue. I have seen some discussion on other Fora about issues with the board and the couplings between coaches. I then coupled the end unit to the drive unit and put it on the track. There was a puff of smoke and one transistor BS3 P88 is now burnt out. The decoder is still working perfectly. Would anyone of you know where I can get a BS3 P88 transistor or a suitable alternative or where I can get a replacement board, they are no longer avaialble from Marklin. If anyone has a schematic of the wiring for the couplings it would help me a lot because I would be able to check the wiring througout the complete railcar. Looking forward to your replies. John

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marklinist5999		#2 Posted : 03 September 2025 14:13:46(UTC) Retweet
Joined: 10/02/2021(UTC) Posts: 4,016 Location: Michigan, Troy		Hello John. Sure seems like you know what you're doing, so I doubt that you have the decoder in upside down or pins misaligned. So yes, either it's been wire incorrectly, or has a broken wire/connection. Are both motor brushes in place and good condition? Check the commutator and clean it. Check for an unsoldered or resoldered wire from the pick-up shoe and ground/frame. Do any of the lights work? Do they reverse direction? That's all I have at the moment. Keep us updated.


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johnmarklin		#3 Posted : 03 September 2025 15:30:04(UTC) Retweet
Joined: 31/03/2011(UTC) Posts: 173 Location: Ireland		Thank you for your suggestions. At the momment my focus is on getting the circuit board/platine sorted. I cannot check anything until i get the damaged transisitor replaced or find a replacement board. i willl keep ye updated. John

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JohnjeanB		#4 Posted : 03 September 2025 17:29:28(UTC) Retweet
Joined: 04/02/2011(UTC) Posts: 3,624 Location: Paris, France		Hello John A few remarks: - if the decoder is fully fonctional, then it can drive the drive unit, redoing the entire wiring which has been totally messed up with (I may be wrong) - if you want to keep the slider inversion feature, Märkllin proposes a unit 60973 and I think ESU proposes one unit too. - some reverse engineering is needed to understand Märklin's wiring with location for 2nd slider, rear headlamps, red marker, internal lighting Märklin"s exploded view does not include any wiring so you have to figure out but this is not outrageously complicated The Koploter 37421 is a digital MM2-MFX unit released in 2008 with a all-included PCB so adding an ESU decoder is probably a total addition with extrnal wiring and cut traces on the PCB. Here is the exploded view diagram: https://www.marklin.fr/produits/details/article/37421 Usually Märklin drives the slider inversion unit, using AUX3 and AUX4 outputs on mSD3 decoders, I think. I cannot say more not having this unit but similar ones like the SBB RaM with 4 cable connections and VT11.5 TEE unit with 10 contacts. Where is located the BS3 P88? On the main PCB outside the decoder? It is probably used to power the internal lighting P88 transistor Of course this is all assumptions on my part so double chek what I say Cheers and good luck Jean
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