Hornby APT (Decoder Wiring Causes Derailing)

[SNIKNNAI]

I purchased the five car set with the extra power car.

I put hornby chips in all the units as instructed, only to find the power cars , both were derailing while exiting curved track.

After a lot of messing about with them and researching the internet I found others who had the same problem.

This didn’t help so I played around with some ideas.

After talking to ste at Grimy times in Warrington it was found that the chip and its wires were the cause, trapped between the body and the chassis.

The answer was to take the tops of the power cars and extend the wires between the chip and its plug. If you cut the wires at the plug and solder new ones to it ,you can then feed the wires up inside the body and re-connect them on top of the motor.

l them did the same to the sound chips I later fitted, with the chip fitting at one end behind the gangways and the speaker went into the space the other end.

the whole setup performed perfectly ever since.

[Fishmanoz]

Would a mod like to make this title a little more meaningful please - Hornby APT Decoder Wiring Causes Derailing.

Mod note - done - R

[ColinB]

This why Hornby should have adopted the 21 pin decoder option years ago. On very many Hornby models I have found the 8 pin decoder with its wiring just won't fit. On a model costing this much you would have thought that they would have spent a bit more time designing the DCC interface properly, especially as I assume the APT already houses a printed circuit board.

[Brew Man]

This why Hornby should have adopted the 21 pin decoder option years ago. On very many Hornby models I have found the 8 pin decoder with its wiring just won't fit. On a model costing this much you would have thought that they would have spent a bit more time designing the DCC interface properly, especially as I assume the APT already houses a printed circuit board.

 

 

@ColinB

Not having yet used a 21 pin decoder, I'm curious to know why/how one would fit more easily than an 8 pin

 

 

[96RAF]

In general, a 21-pin decoder is larger than any 8-pin decoder, but it is a direct fit without a harness.

[Brew Man]

In general, a 21-pin decoder is larger than any 8-pin decoder, but it is a direct fit without a harness.

 

 

I thought that might be it. So still not ideal for locos with restricted space, though because of its size rather than the wiring.

[96RAF]

The thing is BM that being direct fit the loco PCB should have been designed to take such a decoder space-wise. The exception is the old Hornby Sapphire decoder which was a 21-pin unit with a removable 21-8 pin adapter harness and finding room in a steam loco for one of those could be challenging.

[ColinB]

Yes a 21 pin socket is bigger but in something like a diesel or APT there is probably plenty of space. In fact if I remember rightly in the class 50 the space allowed for the 8 pin is about the same size anyway. Either way the APT is a brand new design so you shouldn't be having issues fitting the decoder. Perhaps I have the wrong idea but by default a Hornby loco should allow a standard Hornby decoder to be fitted without any modification. It should be one of the production "sign off" requirements, just like the crossing of double points is (as seen in the series).

[markp123]

I had the exact same problem where the 8 pin wiring fouls the NDM motor housing and thereby causes derailments on 3rd/4th radius curves. It's so easy to do this as there's hardly any room in the 8-pin access hatch.

I also applied the same solution as the OP and opened up the body and moved the chip inside and all derailments were cured.

It's a poor design in my opinion and 21 pin would have been a better choice.

[ColinB]

I managed to get a couple of the really old 21 pin Hornby circuit boards, from when they were fitting LokSound decoders. They fit in the tender in the same place as the 8 pin one. They are such a neat design and so easy to wire. I just cannot understand why they stopped using them, I suppose it is something to do with cost (double sided PCB with plated through holes verses single sided poor quality one). If you take the systems approach a 21 pin decoder socket is a much smaller than 8 pin socket and lead. Funny on the latest 8 pin DCC socket offerings from Hornby I have noticed that they have gone to a dual sided plated through hole version, so I suppose they eventually realised the cost save wasn't worth it (plated through hole pcbs are easier and quicker to wire and more reliable).