UPDATE on Lights causing LM-3S to overheat?

[CPRail]

Thanks for your super-sleuthing Tim!

That board info you found certainly looks like the board I have. I'll lift the LM tonight to be sure, but I think you've figured it out. My poor LM!

I haven't been able to get the LEDs to work, but it's good to know it's a board issue and not me (at least not yet!)

I'll have to check to see if I have any spare boards without those super sized resistors kicking around. If I opt to hard wire everything, do I need to do anything special, or just connect to the appropriate wires off the LM?

[G8B4Life]

Well with the LEDs not working at least you hadn't overruled all electrical theory like I thought you had (thinking the LED's were working) just because it didn't suit your requirements 

Anyway. because visualising is better than reading for things like this; this is what’s happening: Link to circuit simulation

On the left is the one output part of the board with a lamp/globe/bulb hooked up. As you can see the majority of the current flows through the lamp to the resistor. On the right is what you've got, a LED and resistor replacing the lamp. Because the forward voltage required for the diodes CR5 and CR6 is less than the LED (~0.6v each for the diodes vs ~3.5v for the LEDS) the CR diodes conduct with virtually no resistance and your LEDs never turn on.

The board is salvageable if you want to put in the effort, you need to remove the diodes CR5, CR6, CR7, and CR8. Because you put 1k resistors inline with your LEDS you can either remove (replace with wire) or keep the huge 150 ohm resistors, they won't get hot again with the 1k resistors in series however the extra resistance they add will reduce the brightness of the LED's some more

If you choose to hardwire, just follow the wiring diagram included with every 9 pin LM  There's nothing special to do.

- Tim

[CPRail]

Hi All,

There were requests for various voltage readings and I recorded these last night.

Voltage on the Rails: 16.20 V
Voltage seen by the loco (at the connections to the board): approx 15.88 V (it kept fluctuating)

Voltage across the big white/grey resistors:
Front (running the Headlight): average 9.5 V (slight fluctuations)
Rear (running the Gyra-Lite): cycling between 1.75 - 9.5 V

I was able to test my installed LEDs and they are working as advertised. Just need to determine best hook-up option - new board or a hardwire situation.

Did I miss anything?