Paul-380474 Posted August 14 Share Posted August 14 I expect this has been discussed many times., however... What is the point of a 21 pin decoder socket in a steam engine which only has the basic functions? Is it because of the number of pickups?? If so, how should it be wired if the loco is not dcc ready. Or should I just use 8 pin in this case? Paul Link to comment Share on other sites More sharing options...
96RAF Posted August 14 Share Posted August 14 Some steam engines have use for several functions, like lighting, fire-box glow, steam, etc. If a basic motor only steamer then an 8-pin decoder is ample. Link to comment Share on other sites More sharing options...
ColinB Posted August 14 Share Posted August 14 28 minutes ago, Paul-380474 said: I expect this has been discussed many times., however... What is the point of a 21 pin decoder socket in a steam engine which only has the basic functions? Is it because of the number of pickups?? If so, how should it be wired if the loco is not dcc ready. Or should I just use 8 pin in this case? Paul You are absolutely right for most locos you don't need the extra functionality a 21 pin decoder gives you. From a practical point of view, fitting it is an awful lot easier you don't have that long length of wire draping everywhere. The other advantage I like is you can wire the speaker permanently to the loco without having to connect it to the decoder. One less thing for the wires to drop off when you remove the decoder. Hornby do some nice 21 pin sockets on PCBs which you can buy as a spare part. Link to comment Share on other sites More sharing options...
Paul-380474 Posted August 15 Author Share Posted August 15 20 hours ago, 96RAF said: Some steam engines have use for several functions, like lighting, fire-box glow, steam, etc. If a basic motor only steamer then an 8-pin decoder is ample. I have purchased some Bachmann steam engines recently which only have the 'movement' function but are 21 pin. Hence my puzzlement. Now I have a couple of pre-dcc Bachmann to hard wire with dcc I was concerned that 8 pin would not be compatible. My thought is this ... what do the other 17 wires do?! (Yes I know, extra functions), but on those factory fitted basic dcc Bachmanns what was the thinking? Do they just use the four wires or is there more to it? ColinB makes a good point about tidiness, but I heard somewhere about Bachmanns needing 21 pin as they had extra pickups from the track. I have no idea if this is just speculation or rumour however. I suppose I should dismantle one and examine the wiring. However, my wiring skills have already cost me two decoders (I released the magic smoke from them) and so I was hoping for wise words of advice before plugging in the soldering iron. Link to comment Share on other sites More sharing options...
96RAF Posted August 15 Share Posted August 15 These are the pinouts for a TXS 21 pin decoder. Compare with other MTC 21 pin decoders. Link to comment Share on other sites More sharing options...
ColinB Posted August 15 Share Posted August 15 No there are no extra pickups, when designers/engineers design things generally they do a bit of forward thinking in what might we need for the future. To use one part for all your products makes assembly easier. So Bachmann standardised on a 21 pin decoder on some of their older locos they used an 8 pin but then moved to the 21 pin. On a lot of their tank locos they use the Plux18 but that is more to do with space limitations. The 8 pin suffers from a lot of design issues, there is that mountain of wire to worry about, then there is that trailing extra function lead ready to short out on any available piece of metal, you need to add extra pads to the PCB for the speaker wires and finally the sockets are terrible (well the older Hornby ones are), a constant source of bad connections. Of course finally you can get the connection 180 degrees out of phase meaning that as a supplier you get reports of the lights not working simply because the connector is in the wrong way round. All these issues are solved by the 21 pin arrangement although the PCB it sits on is generally larger. Link to comment Share on other sites More sharing options...
Paul-380474 Posted August 15 Author Share Posted August 15 On 14/08/2024 at 10:45, 96RAF said: Some steam engines have use for several functions, like lighting, fire-box glow, steam, etc. If a basic motor only steamer then an 8-pin decoder is ample. I have purchased some Bachmann steam engines recently which only have the 'movement' function but are 21 pin. Hence my puzzlement. Now I have a couple of pre-dcc Bachmann to hard wire with dcc I was concerned that 8 pin would not be compatible. My thought is this ... what do the other 17 wires do?! (Yes I know, extra functions), but on those factory fitted basic dcc Bachmanns what was the thinking? Do they just use the four wires or is there more to it? ColinB makes a good point about tidiness, but I heard somewhere about Bachmanns needing 21 pin as they had extra pickups from the track. I have no idea if this is just speculation or rumour however. I suppose I should dismantle one and examine the wiring. However, my wiring skills have already cost me two decoders (I released the magic smoke from them) and so I was hoping for wise words of advice before plugging in the soldering iron. Link to comment Share on other sites More sharing options...
Paul-380474 Posted August 15 Author Share Posted August 15 Thanks 96RAF and ColinB. All very informative. I see that it is a four wire job regardless of number of pins, and the reason for 21 pin being standardisation. I can now safely move on to configuring these locos for dcc (well, as safe as I will ever be with fiddly wiring. :) ) Paul Link to comment Share on other sites More sharing options...
ColinB Posted August 15 Share Posted August 15 17 minutes ago, Paul-380474 said: Thanks 96RAF and ColinB. All very informative. I see that it is a four wire job regardless of number of pins, and the reason for 21 pin being standardisation. I can now safely move on to configuring these locos for dcc (well, as safe as I will ever be with fiddly wiring. 🙂 ) Paul As I said earlier Hornby make some excellent 21 pin PCBs they were originally for West Country locos. They have ids on the PCB for track left and right with labels TL and TR and M1 and M2 for motor. So it is extremely difficult to get it wrong. They also seem really good quality. The big issue with the 8 pin sockets is the early PCBs from Hornby are such bad quality that it is amazingly easy to create a solder bridge between pins without realising. If it happens between 1 and 8 or 4 and 5, it blows the decoder. 1 Link to comment Share on other sites More sharing options...
Deem Posted August 17 Share Posted August 17 On 15/08/2024 at 15:02, ColinB said: As I said earlier Hornby make some excellent 21 pin PCBs they were originally for West Country locos. They have ids on the PCB for track left and right with labels TL and TR and M1 and M2 for motor. So it is extremely difficult to get it wrong. They also seem really good quality. The big issue with the 8 pin sockets is the early PCBs from Hornby are such bad quality that it is amazingly easy to create a solder bridge between pins without realising. If it happens between 1 and 8 or 4 and 5, it blows the decoder. As I am learning about this hobby, to make life easy for myself, I can save this thread so, as and when I needed to order these PCB, part number is X7880 and here is the picture. Link to comment Share on other sites More sharing options...
ColinB Posted August 17 Share Posted August 17 Trouble is this is Hornby, these will have a limited life span, once they are sold out that is it. Link to comment Share on other sites More sharing options...
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