norman Posted September 1, 2021 Share Posted September 1, 2021 To fit a decoder you need to remove the Heljan PCB. Do you need to add resistors for the lighting? Link to post Share on other sites More sharing options...
smokebox Posted September 1, 2021 Share Posted September 1, 2021 Afaik, if the existing lighting uses bulbs then you will probably need to replace them with LEDs and resistors. Bulbs take too much current and can cause decoder damage. Link to post Share on other sites More sharing options...
norman Posted September 1, 2021 Author Share Posted September 1, 2021 No the lights are all LEDs already. I think only the very early Heljan diesels used bulbs. Link to post Share on other sites More sharing options...
mikeg Posted September 2, 2021 Share Posted September 2, 2021 Norman, you need resistance for the leds if you remove the existing PCB I think the inrush current from the chip can kill the leds. regards Mike Link to post Share on other sites More sharing options...
norman Posted September 2, 2021 Author Share Posted September 2, 2021 Hi Mike Sorry but that's not correct. I have removed the Heljan PCB when fitting a Zimo decoder and the LED lights work perfectly as they are protected by surface mount resistors locally. I am still wondering why the two banks of very small resistors are fitted. They are only about 2 ohms each and they have no effect upon the function outputs I think they must be something to do with radio and TV interference suppression. Link to post Share on other sites More sharing options...
mikeg Posted September 3, 2021 Share Posted September 3, 2021 Norman, when I did my class 31 several years ago I was told that they were there to stop switch on inrush current from the DCC system, and that I should provide a new resister for each of the LEDs which I thought I had but I missed the cab lights and as I had left the loco on the layout when I switched the power on there was a bright flash from the cab. The newer locos might have been changed as I know that the class 60 is wired opposite to most of the other locos for the LEDs! I was going by what I had been told and thought it applied to all the Heljan fleet. regards mike Link to post Share on other sites More sharing options...
charliepetty Posted September 3, 2021 Share Posted September 3, 2021 When using ESU XL Decoders with Legomanbiffo Sounds, we always suggest: TRKL Track pickup TRKR Track pickup MOT+ Motor MOT- Motor U+ Requires 1K Resistor FL White side lights RL White side lights AUX1 Fan (also engine room Class 60) AUX2 Red tail lights AUX3 Red tail lights AUX4 Cab lights AUX5 Cab light AUX6 Side and Head (Class 60) AUX7 Side and Head (Class 60) SPK1+ Speaker SPK1- Speaker Charlie-Legomanbiffo/DCKits 1 Link to post Share on other sites More sharing options...
norman Posted September 3, 2021 Author Share Posted September 3, 2021 Charlie There is nothing fundamentally wrong with 2 x 1k resistors - it just means that the LEDs are very slightly dimmed. Link to post Share on other sites More sharing options...
blueeighties Posted September 5, 2021 Share Posted September 5, 2021 Resistors are not required on any of the Heljan diesels when DCC chip fitting, with the exception of the early filament bulb fitted locos, first issue class 37, and 47. Everything else have resistors built into the led board. 1 Link to post Share on other sites More sharing options...
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