DCC in Hornby Schools Class

[ColinB]

I have just bought a Schools Class loco that was fitted with a Zimo Sound Decoder. It wasn't until I tried it that I found it had it. The loco was only £45 so I got a good deal. Anyway I have had a lot of issues with it, mainly to do with pickups, hence why I suspect the other person sold it. The big concern I have, is that it has loco lights, whilst the dcc chip is in the tender. So my question is, how does the dcc chip control the lights in the loco (can, firebox and front lights), there is not enough connections on the loco tender connector (only four), so is there another dcc chip in the loco? I have taken the loco apart, but all the electronics is buried under gel, so I do not want to go any further for fear of damaging it. I assume this is an issue with lots of Hrnby Locos with the DCC chip in the tender.

[96RAF]

A picture of the gel thing would be useful Colin.

It is not normal Hornby practice to ‘pot’ their electronics, so likely done by the previous owner, who may even have rigged the loco lights to work from DCC track voltage direct.

[ColinB]

No, it is not running from the track directly, I checked that. Each function works on a DCC function, 0 = front lights on, 4 = cab light,  2 = firebox. It is ever so tight in there so I have to very careful, there is a mass of very thin wires disappearing into the get, even with a photo it will not show much. I think it must have a separate dcc controller to control the lights, as the track connections are split one wire goes to the tender the other to the gel. I am electronics engineer that used to work on microprocessors, so I can see no other way it could do it without more wires. Unfortunately, I am not an expert on DCC, is it position to program two modules ate the same time? I suppose what I need to do is split the loco from tender, program the loco with an address then program the tender with a different address. Then see if the lights respond to the loco address or the tender, then I will know. Must be a very small DCC chip if it has one.

 

[Howbi]

Hi Colin..........the service sheet I use for my Schools is HSS 330C which probably applies to your model.......Re: pick-ups, the front bogie is wired as are the main drivers but one axle has traction tyres and the Tender has pick-ups on front and rear axles so it looks as if the main decoder in the tender is relying solely on those which could be insufficient for reliable running..........HB

[ColinB]

Found it, yes it has a sepate DCC chip. I split the loco and tender and programmed them with different addresses. Placed just the loco on the test track, with no tender and the cab lights work on function 1, firebox on function 2. The main dcc sound chip is in the tender, so there must be a separate DCC chip in the loco, under all that gel/silicon. The person that owned this before me must have spent a fortune on DCC. Incidently, I suspect the 4 pin connector is the reason for poor running, the connections look like they have been severly hacked, so I will replace it (they are out of stock on Peters Spares, but EBay has them). 

 

[Chrissaf]

@ColinB,

Can I humbly suggest that next time you do not use the blue button. This is not a 'Reply to this post' button. It is best if you write your reply in the 'Reply to this post' text box at the bottom of the page and click the green 'Reply' button.

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Not having a go, using the blue button is something all relative newbies on the forum seem to do for some reason. I blame the forum SW developers for putting it there, just where a 'Reply' button is expected to be.

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The example reproduced below indicates that you did try to remove the previous quote. But you ended up with your new text trapped in the yellow quote box. This makes it very difficult to see at a glance what is a new post and what is an errored re-quote. If you just use the 'Reply' text box at the bottom of the page then not only can this yellow quote box error be avoided, but it is less work for you to do too. If you just want to indicate that you are replying to a particular forum member, just start your reply with @username where username is the member that you want to bring to the attention of. As I did with the @ColinB at the start of this reply.

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[96RAF]

It is not unusual to run two or more decoders on the same address and what your loco owner has done is probably a reasonably easy way of doing it - one for the loco lights and one for the tender activity.

 

The main thing is to ensure that the function mapping of both decoders is matched or you run both deocders on different addresses in a consist, hence you can action each decoders functions individually (decoder and controller consist capability dependant of course).

[ColinB]

I have eventually got to the extra module in the Schools loco. Unfortunately, since I bought it it has slowly been coming apart, so I have bought a replacement body to transfer every thing to. Does anyone know what module this is? It just controls the front lights and firebox, the main DCC module is in the tender. The coin is a 5 pence piece, it is really small.  I would really like to buy some more, but I haven't any idea who makes it./media/tinymce_upload/bce474e6080bb3ff3aed16f6d3a3909e.jpg

[96RAF]

You can get function only and sound only decoders and this one looks a bit like an N gauge ESU decoder likely fitted in the loco to serve those lighting functions you describe due to its compact size.

 

e.g. https://images.app.goo.gl/McVy7cE8znasAMKt7

 

Rewiring it may be a problem as the wiring looks to be in poor condition.

[ColinB]

I finally found what it was, it is a reduced function decoder made by Zimo it is a MX681. Yes you are right the wiring is terrible, looking at the installation it looks like an animal fitted it. I donned my glasses and rewired it, I have also positioned it in front of the motor, where there is a little more space (not much room in a Schols class loco).