UPDATE on Lights causing LM-3S to overheat?

[CPRail]

Reference my previous post:https://rpug.pdc.ca/index.php/topic,1679.0.html

This weekend, I pulled out all the bulbs and replaced them with surface mount LEDs. I wired them up, including the resistors on the negative side. Went to hook them up on the board and couldn't get them to work.

Pulled out the old multimeter and we are getting juice to the connections, which I expected as the original light-bulbs were working.

Then, when taking the loco off the rails, I almost burnt my fingertips on the whitish-gray resistors (I'm guessing) hanging on the bottom of the board just above the flywheels! See photo 4.

Wok the heck? Keep in mind, I had the light functions turned on for maybe 30 seconds prior to testing with the multi-meter. The rear resistor was cooler than the front, but still warm. I'm guessing that is due to it driving the gyra-lite so the voltage goes up and down, while the headlight one is constant. NOTE: I did not have any LEDs or bulbs hooked up when I checked with the multi-meter.

Time to pause and ask the experts!!

Guess I found why the LM-3S was getting overheat messages with these little Chernobyls sitting under the board!

So, couple of questions:
1. What causes those resistors to get Rocket Hot in such a short period?
2. How do I test these surface mount LEDs before hooking them up to the module board?
3. What am I doing wrong?

[CPRail]

Adding pictures

[CPRail]

Last set of pics.

[G8B4Life]

At that size and body colour those are likely to be inductors, not resistors. If so they are part of of an RF suppression circuit on the motherboard. I've never heard of them getting hot to the touch before though. Anyway, if they are inductors it's best to remove them (replaced by a plain wire) as they just cause trouble for modern control gear. I talk about the why they are there briefly in this post.

Let's make sure they are inductors though, As I've just located a resistor with the same apparent size (but different colour, resistor brown) on a motherboard here. You'll need to check the under side of the circuit board to see what they are labelled as to 100% absolutely confirm. If they are labelled as L such as L1, L2 then they are inductors. If labelled as R such as R1, R2 then they are resistors.


I don't recall asking this simple question, did you ever get the over temp warnings when running without the lights on or having the lights on while not running? If we didn't ask/try this we could have saved ourselves a whole lot of searching.

- Tim

[CPRail]

Hey Tim,

Let me check on the components. Now that the lights are disconnected, I can do a test run as well. Stay tuned.