Cab Lights Not Working.

[geejbee]

Hello to All

I have the class 71, R3374 and the cab lights have stopped working. The connections within the body seem ok. Is there anywhere else I can look please?

[Jupiter 1707822591]

Are they switched on under the chassis

Check that the body is on correctly and if it uses spingy type connectors from the chassis to body .

[geejbee]

Thanks Jupiter.

Yes I've checked the things you mention and everything seems in order. The lights just failed as I was using the loco. Never had an issue previously. I guess there is a failure in the circuitry somewhere.

[ColinB]

The favorite has got to be a wire fell off or not soldered correctly when it was made. The constant vibration may have made it come loose. LEDs very rarely fail but I suppose they do occasionally. Alternately, the DCC port may have become damaged and can no longer drive that channel. What make of decoder are you using?

[Jupiter 1707822591]

Thanks Jupiter.

Yes I've checked the things you mention and everything seems in order. The lights just failed as I was using the loco. Never had an issue previously. I guess there is a failure in the circuitry somewhere.

 

 

Meter out job then .

[Going Spare]

As you have not reacted to ColinB's post, would we be correct in assuming you are using DC rather than DCC control?

[Jupiter 1707822591]

As you have not reacted to ColinB's post, would we be correct in assuming you are using DC rather than DCC control?

 

 

The op uses a select .

[Going Spare]

In that case, could you have turned them off without realising you had done it? (I am not a DCC user!)

[geejbee]

Hello

Sorry for my lack of response to your replies, I've not been too good.

Decoder is a laisdcc. I will try to borrow a Hornby from one of my other locos and see if it solves the problem. I have to say though that in all other respects the laisdcc has performed very well and is small enough to install in the body.

[geejbee]

Hello again

I have fitted a Hornby decoder but the problem with the cab lights is still there. I'm not very good with electronics so I guess I will just live with this minor irritation. Thanks again for your input.

[96RAF]

As luck would have it I have the schematic for this loco.

The cab lights are fed from a voltage regulator to a pair of mosfets in common with the front and rear lights, each circuit having its own current limiting resistor, therefore if the running lights work the supply side is good. There is a switch to isolate the rear running lights. As each cab light is powered separately then to have both fail points to the common return side.

The return side of both cab lights is via Diode D10 to pin 3 of the decoder socket. It should be fairly easy to fault find that circuit, but I would put my money on the body to chassis connections.

[ColinB]

I only suggested changing the decoder just in case. So it is not the decoder, I think 96RAF might be right for it to suddenly not work anymore without you doing anything does tend to indicate something electronic. I suppose the pads the springs sit on to connect the body to chassis could have oxidised so the connection is no longer made. I know how annoying it is when the lights don't work.

[geejbee]

Thank you 96RAF I will look again at connections etc as per your post.

[96RAF]

Time for Hornby to bin those dodgy contacts and replace them with proper plunger contacts. Such pogo pin - magnetic connectors are available in many pin number trackways.

https://www.cfeconn.com/spring-loaded/pogo-pin-connectors

https://www.cfeconn.com/wp-content/uploads/2021/08/Magnetic-electrical-connector-usb-charging-for-medical-equipment-M-BP63321-01-2.jpg

Edit - apparently Hornby have adopted these type of connector on new 800, Flirt, and future others.

[ColinB]

96RAF I know Hornby still market that loco but it is incredibly old. I got mine years ago. We all know Hornby does minimal upgrades. I suppose the only upgrade they have done on a lot of steam locos is move the DCC socket to the tender, but they were forced to do that as without it most of their steam locos wouldn't have enough room to fit sound. I think just fitting the DCC in the class 71 is a major effort. The really good bit about the class 71 is that it has a decent pantograph. I think it was the first of their diesel/electric models to drive all wheels.

[96RAF]

I just looked at SS461 and there doesn’t even seem to be a decoder socket on the CL 71. The body to chassis lights assy doesn’t look to clever either.

Can someone please explain the five conical springs.

[rpjallan]

I have the class 71, R3374 and the cab lights have stopped working. The connections within the body seem ok. Is there anywhere else I can look please?

 

 

It seems that some people have had a problem with tracks in the PCB on these models burning out. Some have removed the PCB altogether and hardwired the decoder including the lighting functions. I have one of these but it hasn't been run a lot & I haven't fitted a decoder yet.

[geejbee]

As a final update I have cleaned the springy connections, tried a different decoder and given it a good talking to but still no cab lights. It actually runs very well so I shall just continue using it as it is.

Regards.

[rpjallan]

As luck would have it I have the schematic for this loco.

 

 

You wouldn't be able to share that with us by any chance, would you?

 

 

[96RAF]

As luck would have it I have the schematic for this loco.

You wouldn't be able to share that with us by any chance, would you?

 

 

Under the terms of my NDA with Hornby I am not allowed to publish such data in the public domain, but on the basis something is better than nothing, I stretch the point to provide folk with indirect knowledge from that data, hence I may crop part of a circuit or quote device part numbers, etc or in the case of a 4-VEP tell of the inter-car connections, etc. Similarly on my web-pages I have provided (with Hornby approval) a Teardown report for most of their DCC and other ‘boxes’,

[ColinB]

It always makes me laugh when firms try to protect their circuit diagrams especially one for a model railway loco. A decent electronics engineer can easily work out the circuit. Some firms even go to the expense of removing the numbers off the integrated circuits.

[96RAF]

Indeed Colin, as seen on the old Bromsgrove models installation guides, there is a guy who reverse engineers the existing boards and modifies them for prototypical lighting. He also did a comparison between the positive and negative earth Class 56s circuits.

As regards proprietary information, how far do you go with putting stuff in the public domain. Lenz and ESU are very forthcoming in many but not all areas, but few other firms publish such data. Do you show circuit diagrams for locos but not decoders; for analogue controllers but not DCC or other kit. We all know from past litigation that the likes of LiasDCC will knock off other peoples stuff anyhow regardless of if the data is published or not, but why make it easy for them.

[ColinB]

You would be amazed what people copy, we found out that the Chinese were doing copies of our diagnostics software and we are not talking simple circuit diagrams but complex lines of code. My attitude when I was in design was you can have all my old stuff as I am working on the new stuff. I have little sympathy for the firm who LaisDCC copied. They obviously decided to save money and get their product manufactured in China, so they were asking for it to be copied, as does anyone that decides to do the same. China does not adhere to any "copyright" agreements. As to the decoders, the complexity is in the software, the circuits are going to be pretty standard, so we come down to basically how much "on board" memory the device has, as that determines how much code you can use.

[96RAF]

@colin

Initially the litigation against LiasDCC was by TCS then according to other forums DCC Concepts has been involved along the line amongst other rebranded decoders e.g. GM, Hattons, etc.

Apparently (again from other forum chat) one of the decoder production house owners walked taking his old software with him and it developed from there.

As you say the IPR investment is mainly in the software, but basic product operational reliability and robustness is down to the hardware, hence a reverse engineered product may look similar but can perform much less well. Look at the Apple charger clones that are truly dangerous inside and easily catch fire giving Apple a bad name.

Anyhow we have been off topic long enough so back to the OP, which is looking like a PCB track fault on the return side.

[rpjallan]

I know some people, mainly with diesel & electric locos of course, who just get rid of the PCBs & hardwire the decoders straight up. In a DCC loco there is really no need for a PCB.

If you look at any of the guides relating to fitting sound into locos with a lack of space, the PCB is the first thing to go.